One document matched: draft-ietf-idr-ls-distribution-03.xml
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<rfc category="std" docName="draft-ietf-idr-ls-distribution-03"
ipr="trust200902">
<front>
<title abbrev="Link-State Info Distribution using BGP">North-Bound
Distribution of Link-State and TE Information using BGP</title>
<author fullname="Hannes Gredler" initials="H." surname="Gredler">
<organization>Juniper Networks, Inc.</organization>
<address>
<postal>
<street>1194 N. Mathilda Ave.</street>
<city>Sunnyvale</city>
<region>CA</region>
<code>94089</code>
<country>US</country>
</postal>
<email>hannes@juniper.net</email>
</address>
</author>
<author fullname="Jan Medved" initials="J." surname="Medved">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>170, West Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>US</country>
</postal>
<email>jmedved@cisco.com</email>
</address>
</author>
<author fullname="Stefano Previdi" initials="S." surname="Previdi">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Via Del Serafico, 200</street>
<city>Rome</city>
<code>00142</code>
<country>Italy</country>
</postal>
<email>sprevidi@cisco.com</email>
</address>
</author>
<author fullname="Adrian Farrel" initials="A." surname="Farrel">
<organization>Juniper Networks, Inc.</organization>
<address>
<postal>
<street>1194 N. Mathilda Ave.</street>
<city>Sunnyvale</city>
<region>CA</region>
<code>94089</code>
<country>US</country>
</postal>
<email>afarrel@juniper.net</email>
</address>
</author>
<author fullname="Saikat Ray" initials="S." surname="Ray">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>170, West Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>US</country>
</postal>
<email>sairay@cisco.com</email>
</address>
</author>
<date day="21" month="May" year="2013"/>
<workgroup>Inter-Domain Routing</workgroup>
<abstract>
<t>In a number of environments, a component external to a network is
called upon to perform computations based on the network topology and
current state of the connections within the network, including traffic
engineering information. This is information typically distributed by
IGP routing protocols within the network</t>
<t>This document describes a mechanism by which links state and traffic
engineering information can be collected from networks and shared with
external components using the BGP routing protocol. This is achieved
using a new BGP Network Layer Reachability Information (NLRI) encoding
format. The mechanism is applicable to physical and virtual IGP links. The
mechanism described is subject to policy control.</t>
<t>Applications of this technique include Application Layer Traffic
Optimization (ALTO) servers, and Path Computation Elements (PCEs).</t>
</abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>The contents of a Link State Database (LSDB) or a Traffic Engineering
Database (TED) has the scope of an IGP area. Some applications, such as
end-to-end Traffic Engineering (TE), would benefit from visibility
outside one area or Autonomous System (AS) in order to make better
decisions.</t>
<t>The IETF has defined the Path Computation Element (PCE) <xref
target="RFC4655"></xref> as a mechanism for achieving the computation of
end-to-end TE paths that cross the visibility of more than one TED or
which require CPU-intensive or coordinated computations. The IETF has
also defined the ALTO Server <xref target="RFC5693"></xref> as an entity
that generates an abstracted network topology and provides it to
network-aware applications.</t>
<t>Both a PCE and an ALTO Server need to gather information about the
topologies and capabilities of the network in order to be able to
fulfill their function.</t>
<t>This document describes a mechanism by which Link State and TE
information can be collected from networks and shared with external
components using the BGP routing protocol <xref
target="RFC4271"></xref>. This is achieved using a new BGP Network Layer
Reachability Information (NLRI) encoding format. The mechanism is
applicable to physical and virtual links. The mechanism described is
subject to policy control.</t>
<t>A router maintains one or more databases for storing link-state
information about nodes and links in any given area. Link attributes
stored in these databases include: local/remote IP addresses,
local/remote interface identifiers, link metric and TE metric, link
bandwidth, reservable bandwidth, per CoS class reservation state,
preemption and Shared Risk Link Groups (SRLG). The router's BGP process
can retrieve topology from these LSDBs and distribute it to a consumer,
either directly or via a peer BGP Speaker (typically a dedicated Route
Reflector), using the encoding specified in this document.</t>
<t>The collection of Link State and TE link state information and its
distribution to consumers is shown in the following figure.</t>
<figure anchor="MECHANISM-OVERVIEW"
title="TE Link State info collection">
<artwork>
+-----------+
| Consumer |
+-----------+
^
|
+-----------+
| BGP | +-----------+
| Speaker | | Consumer |
+-----------+ +-----------+
^ ^ ^ ^
| | | |
+---------------+ | +-------------------+ |
| | | |
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
+-----------+ +-----------+ +-----------+
^ ^ ^
| | |
IGP IGP IGP
</artwork>
</figure>
<t>A BGP Speaker may apply configurable policy to the information that
it distributes. Thus, it may distribute the real physical topology from
the LSDB or the TED. Alternatively, it may create an abstracted
topology, where virtual, aggregated nodes are connected by virtual
paths. Aggregated nodes can be created, for example, out of multiple
routers in a POP. Abstracted topology can also be a mix of physical and
virtual nodes and physical and virtual links. Furthermore, the BGP
Speaker can apply policy to determine when information is updated to the
consumer so that there is reduction of information flow form the network
to the consumers. Mechanisms through which topologies can be aggregated
or virtualized are outside the scope of this document</t>
</section>
<section title="Motivation and Applicability">
<t>This section describes use cases from which the requirements can be
derived.</t>
<section title="MPLS-TE with PCE">
<t>As described in <xref target="RFC4655"></xref> a PCE can be used to
compute MPLS-TE paths within a "domain" (such as an IGP area) or
across multiple domains (such as a multi-area AS, or multiple ASes).
<list style="symbols">
<t>Within a single area, the PCE offers enhanced computational
power that may not be available on individual routers,
sophisticated policy control and algorithms, and coordination of
computation across the whole area.</t>
<t>If a router wants to compute a MPLS-TE path across IGP areas
its own TED lacks visibility of the complete topology. That means
that the router cannot determine the end-to-end path, and cannot
even select the right exit router (Area Border Router - ABR) for
an optimal path. This is an issue for large-scale networks that
need to segment their core networks into distinct areas, but which
still want to take advantage of MPLS-TE.</t>
</list></t>
<t>Previous solutions used per-domain path computation <xref
target="RFC5152"></xref>. The source router could only compute the
path for the first area because the router only has full topological
visibility for the first area along the path, but not for subsequent
areas. Per-domain path computation uses a technique called
"loose-hop-expansion" <xref target="RFC3209"></xref>, and selects the
exit ABR and other ABRs or AS Border Routers (ASBRs) using the IGP
computed shortest path topology for the remainder of the path. This
may lead to sub-optimal paths, makes alternate/back-up path
computation hard, and might result in no TE path being found when one
really does exist.</t>
<t>The PCE presents a computation server that may have visibility into
more than one IGP area or AS, or may cooperate with other PCEs to
perform distributed path computation. The PCE obviously needs access
to the TED for the area(s) it serves, but <xref
target="RFC4655"></xref> does not describe how this is achieved. Many
implementations make the PCE a passive participant in the IGP so that
it can learn the latest state of the network, but this may be
sub-optimal when the network is subject to a high degree of churn, or
when the PCE is responsible for multiple areas.</t>
<t>The following figure shows how a PCE can get its TED information
using the mechanism described in this document.</t>
<figure anchor="PCE-REFERENCE"
title="External PCE node using a TED synchronization mechanism">
<artwork>
+----------+ +---------+
| ----- | | BGP |
| | TED |<-+-------------------------->| Speaker |
| ----- | TED synchronization | |
| | | mechanism: +---------+
| | | BGP with Link-State NLRI
| v |
| ----- |
| | PCE | |
| ----- |
+----------+
^
| Request/
| Response
v
Service +----------+ Signaling +----------+
Request | Head-End | Protocol | Adjacent |
-------->| Node |<------------>| Node |
+----------+ +----------+
</artwork>
</figure>
<t>The mechanism in this document allows the necessary TED information
to be collected from the IGP within the network, filtered according to
configurable policy, and distributed to the PCE as necessary.</t>
</section>
<section title="ALTO Server Network API">
<t>An ALTO Server <xref target="RFC5693"></xref> is an entity that
generates an abstracted network topology and provides it to
network-aware applications over a web service based API. Example
applications are p2p clients or trackers, or CDNs. The abstracted
network topology comes in the form of two maps: a Network Map that
specifies allocation of prefixes to Partition Identifiers (PIDs), and
a Cost Map that specifies the cost between PIDs listed in the Network
Map. For more details, see <xref
target="I-D.ietf-alto-protocol"></xref>.</t>
<t>ALTO abstract network topologies can be auto-generated from the
physical topology of the underlying network. The generation would
typically be based on policies and rules set by the operator. Both
prefix and TE data are required: prefix data is required to generate
ALTO Network Maps, TE (topology) data is required to generate ALTO
Cost Maps. Prefix data is carried and originated in BGP, TE data is
originated and carried in an IGP. The mechanism defined in this
document provides a single interface through which an ALTO Server can
retrieve all the necessary prefix and network topology data from the
underlying network. Note an ALTO Server can use other mechanisms to
get network data, for example, peering with multiple IGP and BGP
Speakers.</t>
<t>The following figure shows how an ALTO Server can get network
topology information from the underlying network using the mechanism
described in this document.</t>
<figure anchor="ALTO-REFERENCE"
title="ALTO Server using network topology information">
<artwork>
+--------+
| Client |<--+
+--------+ |
| ALTO +--------+ BGP with +---------+
+--------+ | Protocol | ALTO | Link-State NLRI | BGP |
| Client |<--+------------| Server |<----------------| Speaker |
+--------+ | | | | |
| +--------+ +---------+
+--------+ |
| Client |<--+
+--------+
</artwork>
</figure>
</section>
</section>
<section title="Carrying Link State Information in BGP">
<t>This specification contains two parts: definition of a new
BGP NLRI that describes links, nodes and prefixes comprising IGP
link state information, and definition of a new BGP path
attribute (BGP-LS attribute) that carries link, node and prefix
properties and attributes, such as the link and prefix metric or
auxiliary Router-IDs of nodes, etc.</t>
<section anchor="TLV-section" title="TLV Format">
<t>Information in the new link state NLRIs and attributes is encoded
in Type/Length/Value triplets. The TLV format is shown in <xref
target="TLV-figure"></xref>.</t>
<figure anchor="TLV-figure" title="TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The Length field defines the length of the value portion in octets
(thus a TLV with no value portion would have a length of zero). The
TLV is not padded to four-octet alignment. Unrecognized types are
preserved and propagated. In order to compare NLRIs with unknown
TLVs all TLVs MUST be ordered in ascending order. If there are
more TLVs of the same type, then the TLVs MUST be ordered
in ascending order of the TLV value within the set of TLVs with
the same type.
All TLVs that are not specified as mandatory are considered
optional.
</t>
</section>
<section title="The Link State NLRI">
<t>The MP_REACH and MP_UNREACH attributes are BGP's containers for
carrying opaque information. Each Link State NLRI describes either a
node, a link or a prefix.</t>
<t>All non-VPN link, node and prefix information SHALL be
encoded using AFI 16388 / SAFI 71. VPN link, node and prefix
information SHALL be encoded using AFI 16388 / SAFI 128.</t>
<t>In order for two BGP speakers to exchange Link-State NLRI, they
MUST use BGP Capabilities Advertisement to ensure that they both are
capable of properly processing such NLRI. This is done as specified in
<xref target="RFC4760"></xref>, by using capability code 1
(multi-protocol BGP), with an AFI 16388 / SAFI 71 and
AFI 16388 / SAFI 128 for the VPN flavor.</t>
<t>The format of the Link State NLRI is shown in the following
figure.</t>
<figure anchor="LSSAFI" title="Link State AFI 16388 / SAFI 71 NLRI Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link-State NLRI (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<figure anchor="LSVPNSAFI" title="Link State VPN AFI 16388 / SAFI 128 NLRI Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Route Distinguisher +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link-State NLRI (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The 'Total NLRI Length' field contains the cumulative
length, in octets, of rest of the NLRI not including the NLRI
Type field or itself. For VPN applications it also includes
the length of the Route Distinguisher.</t>
<t>The 'NLRI Type' field can contain one of the following values:
<list style="hanging">
<t>Type = 1: Node NLRI</t>
<t>Type = 2: Link NLRI</t>
<t>Type = 3: IPv4 Topology Prefix NLRI</t>
<t>Type = 4: IPv6 Topology Prefix NLRI</t>
</list></t>
<t>The Node NLRI (NLRI Type = 1) is shown in the following figure.</t>
<figure anchor="NODE-NLRI" title="The Node NLRI format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The Link NLRI (NLRI Type = 2) is shown in the following figure.</t>
<figure anchor="LINK-NLRI" title="The Link NLRI format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Link Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the
same format as shown in the following figure.</t>
<figure anchor="PREFIX-NLRI"
title="The IPv4/IPv6 Topology Prefix NLRI format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptor (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Prefix Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The 'Protocol-ID' field can contain one of the following values:
<list style="hanging">
<t>Protocol-ID = 0: Unknown, The source of NLRI information could
not be determined</t>
<t>Protocol-ID = 1: IS-IS Level 1, The NLRI information has been
sourced by IS-IS Level 1</t>
<t>Protocol-ID = 2: IS-IS Level 2, The NLRI information has been
sourced by IS-IS Level 2</t>
<t>Protocol-ID = 3: OSPF, The NLRI information has been sourced by
OSPF</t>
<t>Protocol-ID = 4: Direct, The NLRI information has been sourced
from local interface state</t>
<t>Protocol-ID = 5: Static, The NLRI information has been sourced
by static configuration</t>
</list>
</t>
<t>Both OSPF and IS-IS may run multiple routing protocol
instances over the same link. See <xref
target="RFC6822"></xref> and <xref
target="RFC6549"></xref>. These instances define independent
"routing universes". The 64-Bit 'Identifier' field is
used to identify the "routing universe" where the NLRI belongs.
The NLRIs representing IGP objects (nodes, links or prefixes)
from the same routing universe MUST have the same 'Identifier'
value; NLRIs with different 'Identifier' values MUST be considered
to be from different routing universes.
Table <xref target="well_known_instances"></xref> lists the
'Identifier' values that are defined as well-known in this draft.
</t>
<texttable anchor="well_known_instances"
title="Well-known Instance Identifiers">
<ttcol align="center">Identifier</ttcol>
<ttcol align="left">Routing Universe</ttcol>
<c>0</c>
<c>L3 packet topology</c>
<c>1</c>
<c>L1 optical topology</c>
</texttable>
<t>
Each Node Descriptor and Link Descriptor consists of one or
more TLVs described in the following sections.
</t>
<section title="Node Descriptors">
<t>Each link is anchored by a pair of Router-IDs that are
used by the underlying IGP, namely, 48 Bit ISO
System-ID for IS-IS and 32 bit Router-ID for OSPFv2 and
OSPFv3. An IGP may use one or more additional
auxiliary Router-IDs, mainly for traffic engineering
purposes. For example, IS-IS may have one or more IPv4 and
IPv6 TE Router-IDs <xref target="RFC5305"/>, <xref
target="RFC6119"/>. These auxiliary Router-IDs MUST be
included in the link attribute described in Section <xref
target="link_attribute"/>.
</t>
<t>It is desirable that the Router-ID assignments inside the
Node Descriptor are globally unique. However there may be
Router-ID spaces (e.g. ISO) where no global registry
exists, or worse, Router-IDs have been allocated following
private-IP <xref target="RFC1918">RFC 1918</xref>
allocation. We use Autonomous System (AS) Number and BGP-LS
Identifier in order to disambiguate the Router-IDs, as
described in <xref target="gbl_uniqueness"></xref>.</t>
<section anchor="gbl_uniqueness"
title="Globally Unique Node/Link/Prefix Identifiers">
<t>One problem that needs to be addressed is the ability to identify
an IGP node globally (by "global", we mean within the BGP-LS
database collected by all BGP-LS speakers that talk to each other).
This can be expressed through the following two requirements:</t>
<t>(A) The same node must not be represented by two keys (otherwise
one node will look like two nodes).</t>
<t>(B) Two different nodes must not be represented by the same key
(otherwise, two nodes will look like one node).</t>
<t>We define an "IGP domain" to be the set of nodes
(hence, by extension links and prefixes), within which,
each node has a unique IGP representation by using the
combination of Area-ID, Router-ID, Protocol, Topology-ID,
and Instance ID. The problem is that BGP may receive
node/link/prefix information from multiple independent
"IGP domains" and we need to distinguish between them.
Moreover, we can't assume there is always one and only one
IGP domain per AS. During IGP transitions it may
happen that two redundant IGPs are in place.</t>
<t>In section <xref target="node_desc_tlvs"></xref> a set of sub-TLVs
is described, which allows to specify a flexible key for any given
Node/Link information such that global uniqueness of the NLRI is
ensured.
</t>
</section>
<section anchor="LOCALNODEDESC" title="Local Node Descriptors">
<t>The Local Node Descriptors TLV contains Node
Descriptors for the node anchoring the local end of the
link. This is a mandatory TLV in all three types of
NLRIs. The length of this TLV is variable. The value
contains one or more Node Descriptor Sub-TLVs defined in
<xref target="node_desc_tlvs"></xref>.</t>
<figure anchor="LOCALNODEDESCTLV"
title="Local Node Descriptors TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Node Descriptor Sub-TLVs (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="REMOTENODEDESC" title="Remote Node Descriptors">
<t>The Remote Node Descriptors contains Node Descriptors
for the node anchoring the remote end of the link. This is
a mandatory TLV for link NLRIs. The length of this TLV is
variable. The value contains one or more Node Descriptor
Sub-TLVs defined in <xref
target="node_desc_tlvs"></xref>.</t>
<figure anchor="REMOTENODEDESCTLV"
title="Remote Node Descriptors TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Node Descriptor Sub-TLVs (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="node_desc_tlvs" title="Node Descriptor Sub-TLVs">
<t>The Node Descriptor Sub-TLV type codepoints and lengths are
listed in the following table:</t>
<texttable anchor="table_local_anchor_node_tlv"
title="Node Descriptor Sub-TLVs">
<ttcol align="center">Sub-TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="right">Length</ttcol>
<c>512</c>
<c>Autonomous System</c>
<c>4</c>
<c>513</c>
<c>BGP-LS Identifier</c>
<c>4</c>
<c>514</c>
<c>Area-ID</c>
<c>4</c>
<c>515</c>
<c>IGP Router-ID</c>
<c>Variable</c>
</texttable>
<t>The sub-TLV values in Node Descriptor TLVs are defined as
follows:</t>
<t><list style="hanging">
<t hangText="Autonomous System:">opaque value (32 Bit AS
Number)</t>
<t hangText="BGP-LS Identifier:">opaque value (32 Bit
ID). In conjunction with ASN, uniquely identifies the
BGP-LS domain. The combination of ASN and BGP-LS ID MUST
be globally unique. All BGP-LS speakers within an IGP
flooding-set (set of IGP nodes within which an LSP/LSA
is flooded) MUST use the same ASN, BGP-LS ID tuple. If
an IGP domain consists of multiple flooding-sets, then
all BGP-LS speakers within the IGP domain SHOULD use the
same ASN, BGP-LS ID tuple. The ASN, BGP Router-ID tuple
(which is globally unique <xref target="RFC6286"></xref> ) of one of the BGP-LS speakers
within the flooding-set (or IGP domain) may be used for
all BGP-LS speakers in that flooding-set (or IGP
domain).
</t>
<t hangText="Area ID:">It is used to identify the 32 Bit area to
which the NLRI belongs. Area Identifier allows the different NLRIs
of the same router to be discriminated.
</t>
<t hangText="IGP Router ID:">opaque value. This is a
mandatory TLV. For an IS-IS non-Pseudonode, this
contains 6 octet ISO node-ID (ISO system-ID). For an
IS-IS Pseudonode corresponding to a LAN, this contains 6
octet ISO node-ID of the "Designated Intermediate
System" (DIS) followed by one octet nonzero PSN
identifier (7 octet in total). For an OSPFv2 or OSPFv3
non-"Pseudonode", this contains 4 octet Router-ID. For
an OSPFv2 "Pseudonode" representing a LAN, this contains
4 octet Router-ID of the designated router (DR) followed
by 4 octet IPv4 address of the DR's interface to the LAN
(8 octet in total). Similarly, for an OSPFv3
"Pseudonode", this contains 4 octet Router-ID of the DR
followed by 4 octet interface identifier of the DR's
interface to the LAN (8 octet in total). The TLV size in
combination with protocol identifier enables the decoder
to determine the type of the node.
</t>
<!--HG> shall we add a note what to do when a violation is detected ?
i.e. consider the protocol-source being IS-IS and somebody
accidentially encoding just 4 cotets of ID space, should we raise hell or
just proceed with the advertised length field ? -->
<t>There can be at most one instance of each sub-TLV type
present in any Node Descriptor. The TLV ordering within
a Node descriptor MUST be kept in order of increasing
numeric value of type. This needs to be done in order to
compare NLRIs, even when an implementation encounters an
unknown sub-TLV. Using stable sorting an implementation
can do binary comparison of NLRIs and hence allow
incremental deployment of new key sub-TLVs.</t>
</list>
</t>
</section>
<section anchor="MT-ID" title="Multi-Topology ID">
<t >The Multi-Topology ID (MT-ID) TLV carries one or more
IS-IS or OSPF Multi-Topology IDs for a link, node or
prefix.</t>
<t>Semantics of the IS-IS MT-ID are defined in <xref
target="RFC5120">RFC5120, Section 7.2</xref>. Semantics of the OSPF
MT-ID are defined in <xref target="RFC4915">RFC4915,
Section 3.7</xref>. If the value in the MT-ID TLV is
derived from OSPF, then the upper 9 bits MUST be set to 0.
Bits R are reserved, SHOULD be set to 0 when originated and
ignored on receipt.</t>
<t>The format of the MT-ID TLV is shown in the following
figure.
</t>
<figure anchor="MTIDTLV" title="Multi-Topology ID TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length=2*n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R R R R| Multi-Topology ID 1 | .... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// .... |R R R R| Multi-Topology ID n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>where Type is 263, Length is 2*n and n is the number of
MT-IDs carried in the TLV.</t>
<t>The MT-ID TLV MAY be present in a Link Descriptor, a
Prefix Descriptor, or in the BGP-LS attribute of a node
NLRI. In Link or Prefix Descriptor, only one MT-ID TLV
containing only the MT-ID of the topology where the link or
the prefix belongs is allowed. In the BGP-LS attribute of a
node NLRI, one MT-ID TLV containing the array of MT-IDs of
all topologies where the node belongs can be present.
</t>
</section>
</section>
<section title="Link Descriptors">
<t>The 'Link Descriptor' field is a set of Type/Length/Value
(TLV) triplets. The format of each TLV is shown in <xref
target="TLV-section"></xref>. The 'Link descriptor' TLVs
uniquely identify a link among multiple parallel links
between a pair of anchor routers. A link described by the
Link descriptor TLVs actually is a "half-link", a
unidirectional representation of a logical link. In order to
fully describe a single logical link two originating routers
advertise a half-link each, i.e. two link NLRIs are
advertised for a given point-to-point link.</t>
<t>The format and semantics of the 'value' fields in most 'Link
Descriptor' TLVs correspond to the format and semantics of value
fields in IS-IS Extended IS Reachability sub-TLVs, defined in <xref
target="RFC5305"></xref>, <xref target="RFC5307"></xref> and <xref
target="RFC6119"></xref>. Although the encodings for 'Link
Descriptor' TLVs were originally defined for IS-IS, the TLVs can
carry data sourced either by IS-IS or OSPF.</t>
<t>The following TLVs are valid as Link Descriptors in the Link
NLRI:</t>
<texttable anchor="table_link_descriptor_tlv"
title="Link Descriptor TLVs">
<ttcol align="center">TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="center">IS-IS TLV/Sub-TLV</ttcol>
<ttcol align="left">Value defined in:</ttcol>
<c>258</c>
<c>Link Local/Remote Identifiers</c>
<c>22/4</c>
<c><xref target="RFC5307"></xref>/1.1</c>
<c>259</c>
<c>IPv4 interface address</c>
<c>22/6</c>
<c><xref target="RFC5305"></xref>/3.2</c>
<c>260</c>
<c>IPv4 neighbor address</c>
<c>22/8</c>
<c><xref target="RFC5305"></xref>/3.3</c>
<c>261</c>
<c>IPv6 interface address</c>
<c>22/12</c>
<c><xref target="RFC6119"></xref>/4.2</c>
<c>262</c>
<c>IPv6 neighbor address</c>
<c>22/13</c>
<c><xref target="RFC6119"></xref>/4.3</c>
<c>263</c>
<c>Multi-Topology Identifier</c>
<c>---</c>
<c><xref target="MT-ID"/></c>
</texttable>
</section>
<section anchor="PREFIXDESC" title="Prefix Descriptors">
<t>The 'Prefix Descriptor' field is a set of Type/Length/Value (TLV)
triplets. 'Prefix Descriptor' TLVs uniquely identify an IPv4 or IPv6
Prefix originated by a Node. The following TLVs are valid as Prefix
Descriptors in the IPv4/IPv6 Prefix NLRI:</t>
<texttable anchor="table_prefix_descriptor_tlv"
title="Prefix Descriptor TLVs">
<ttcol align="center">TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="center">Length</ttcol>
<ttcol align="left">Value defined in:</ttcol>
<c>263</c>
<c>Multi-Topology Identifier</c>
<c>variable</c>
<c><xref target="MT-ID"/></c>
<c>264</c>
<c>OSPF Route Type</c>
<c>1</c>
<c><xref target="OSPFRTETYPE"/></c>
<c>265</c>
<c>IP Reachability Information</c>
<c>variable</c>
<c><xref target="IPREACHINFO"/></c>
</texttable>
<section anchor="OSPFRTETYPE" title="OSPF Route Type">
<t> OSPF Route Type is an optional TLV that MAY be present in Prefix
NLRIs. It is used to identify the OSPF route-type of the prefix. It
is used when an OSPF prefix is advertised in the OSPF domain with
multiple different route-types. The Route Type TLV allows to
discriminate these advertisements. The format of the OSPF Route Type
TLV is shown in the following figure.</t>
<figure anchor="ROUTETYPETLV" title="OSPF Route Type TLV Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Type |
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>where the Type and Length fields of the TLV are defined in
<xref target="table_prefix_descriptor_tlv"/>. The OSPF Route Type
field values are defined in the OSPF protocol, and can be one of
the following:
<list style="hanging">
<t>Intra-Area (0x1)</t>
<t>Inter-Area (0x2)</t>
<t>External 1 (0x3)</t>
<t>External 2 (0x4)</t>
<t>NSSA 1 (0x5)</t>
<t>NSSA 2 (0x6)</t>
</list>
</t>
</section>
<section anchor="IPREACHINFO" title="IP Reachability Information">
<t>The IP Reachability Information is a mandatory TLV that
contains one IP address prefix (IPv4 or IPv6) originally
advertised in the IGP topology. Its purpose is to glue a particular
BGP service NLRI vi virtue of its BGP next-hop
to a given Node in the LSDB. A router SHOULD advertise an
IP Prefix NLRI for each of its BGP Next-hops.
The format of the IP Reachability
Information TLV is shown in the following figure:</t>
<figure anchor="IPREACHABILITYTLV" title="IP Reachability Information TLV Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The Type and Length fields of the TLV are defined in
<xref target="table_prefix_descriptor_tlv"/>. The
following two fields determine the address-family
reachability information. The 'Prefix Length' field
contains the length of the prefix in bits. The 'IP
Prefix' field contains the most significant octets of
the prefix; i.e., 1 octet for prefix length 1
up to 8, 2 octets for prefix length 9 to 16, 3 octets
for prefix length 17 up to 24 and 4 octets for prefix
length 25 up to 32, etc.</t>
</section>
</section>
</section>
<section title="The LINK_STATE Attribute">
<t>This is an optional, non-transitive BGP attribute that is used to
carry link, node and prefix parameters and attributes. It is defined
as a set of Type/Length/Value (TLV) triplets, described in the
following section. This attribute SHOULD only be included with Link
State NLRIs. This attribute MUST be ignored for all other address-families.</t>
<section title="Node Attribute TLVs">
<t>Node attribute TLVs are the TLVs that may be encoded in
the BGP-LS attribute with a node NLRI. The following node
attribute TLVs are defined:</t>
<texttable anchor="node-attribute_tlv" title="Node Attribute TLVs">
<ttcol align="center">TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="right">Length</ttcol>
<ttcol align="left">Value defined in:</ttcol>
<c>263</c>
<c>Multi-Topology Identifier</c>
<c>variable</c>
<c><xref target="MT-ID"/></c>
<c>1024</c>
<c>Node Flag Bits</c>
<c>1</c>
<c><xref target="NODEFLAGBITS"/></c>
<c>1025</c>
<c>Opaque Node Properties</c>
<c>variable</c>
<c><xref target="OPAQUENODE"/></c>
<c>1026</c>
<c>Node Name</c>
<c>variable</c>
<c><xref target="NODENAME"/></c>
<c>1027</c>
<c>IS-IS Area Identifier</c>
<c>variable</c>
<c><xref target="ISISAREA"/></c>
<c>1028</c>
<c>IPv4 Router-ID of Local Node</c>
<c>4</c>
<c><xref target="RFC5305"></xref>/4.3</c>
<c>1029</c>
<c>IPv6 Router-ID of Local Node</c>
<c>16</c>
<c><xref target="RFC6119"></xref>/4.1</c>
</texttable>
<section anchor="NODEFLAGBITS" title="Node Flag Bits TLV">
<t>The Node Flag Bits TLV carries a bit mask describing node
attributes. The value is a variable length bit array of flags, where
each bit represents a node capability.</t>
<figure anchor="node_flag_bits" title="Node Flag Bits TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|T|E|A| Reserved|
+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The bits are defined as follows:</t>
<texttable anchor="table_node_flag_bits_tlv"
title="Node Flag Bits Definitions">
<ttcol align="center">Bit</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="left">Reference</ttcol>
<c>'O'</c>
<c>Overload Bit</c>
<c><xref target="RFC1195"></xref></c>
<c>'T'</c>
<c>Attached Bit</c>
<c><xref target="RFC1195"></xref></c>
<c>'E'</c>
<c>External Bit</c>
<c><xref target="RFC2328"></xref></c>
<c>'A'</c>
<c>ABR Bit</c>
<c><xref target="RFC2328"></xref></c>
<c>Reserved</c>
<c>Reserved for future use</c>
<c></c>
</texttable>
</section>
<section anchor="ISISAREA"
title="IS-IS Area Identifier TLV">
<t>An IS-IS node can be part of one or more IS-IS
areas. Each of these area addresses is carried in the IS-IS
Area Identifier TLV. If more than one Area Addresses are
present, multiple TLVs are used to encode them. The IS-IS
Area Identifier TLV may be present in the LINK_STATE
attribute only with the Link State Node NLRI.
</t>
<figure anchor="ISISAREAIDTLV" title="IS-IS Area Identifier TLV Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Area Identifier (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="NODENAME"
title="Node Name TLV">
<t>The Node Name TLV is optional. Its structure and encoding
has been borrowed from <xref target="RFC5301"/>.
The value field identifies the symbolic name of the router node.
This symbolic name can be the FQDN for the router, it can be a
subset of the FQDN, or it can be any string operators want to
use for the router. The use of FQDN or a subset of it is
strongly recommended.
</t>
<t>
The Value field is encoded in 7-bit ASCII. If a user-interface for
configuring or displaying this field permits Unicode characters, that
user-interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in <xref target="RFC3490"/>
to achieve the correct format for transmission or display.
</t>
<t>Altough <xref target="RFC5301"/> is a IS-IS specific extension,
usage of the Node Name TLV is possible for all protocols. How
a router derives and injects node names for e.g. OSPF nodes,
is outside of the scope of this document.
</t>
<figure anchor="optional-node-name-tlv"
title="Node Name format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Node Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="aux_routerid_node" title="Local IPv4/IPv6 Router-ID">
<t>The local IPv4/IPv6 Router-ID TLVs are used to describe
auxiliary Router-IDs that the IGP might be using,
e.g., for TE and migration purposes like correlating a Node-ID between
different protocols. If there is more than one auxiliary
Router-ID of a given type, then each one is encoded in its own TLV.
</t>
</section>
<section anchor="OPAQUENODE"
title="Opaque Node Attribute TLV">
<t>The Opaque Node attribute TLV is an envelope that
transparently carries optional node attribute TLVs advertised by a
router. An originating router shall use this TLV
for encoding information specific to the protocol advertised
in the NLRI header Protocol-ID field or new protocol extensions
to the protocol as advertised in the NLRI header
Protocol-ID field for which there is no protocol neutral
representation in the BGP link-state NLRI.
A router for example could use this extension in order to
advertise the native protocols node attribute TLVs,
such as the OSPF Router Informational Capabilities
TLV defined in <xref target="RFC4970"></xref>, or the IGP TE Node
Capability Descriptor TLV described in <xref
target="RFC5073"></xref>. </t>
<figure anchor="optional_opaque_node-attribute_tlv"
title="Opaque Node attribute format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque node attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
</section>
<section anchor="link_attribute" title="Link Attribute TLVs">
<t>Link attribute TLVs are TLVs that may be encoded in the
BGP-LS attribute with a link NLRI. Each 'Link Attribute' is
a Type/Length/Value (TLV) triplet formatted as defined in
<xref target="TLV-section"></xref>. The format and semantics
of the 'value' fields in some 'Link Attribute' TLVs
correspond to the format and semantics of value fields in
IS-IS Extended IS Reachability sub-TLVs, defined in <xref
target="RFC5305"></xref> and <xref
target="RFC5307"></xref>. Other 'Link Attribute' TLVs are
defined in this document. Although the encodings for 'Link
Attribute' TLVs were originally defined for IS-IS, the TLVs
can carry data sourced either by IS-IS or OSPF.</t>
<t>The following 'Link Attribute' TLVs are are valid in the
LINK_STATE attribute:</t>
<texttable anchor="table_link_attribute_tlv"
title="Link Attribute TLVs">
<ttcol align="center">TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="center">IS-IS TLV/Sub-TLV</ttcol>
<ttcol align="left">Defined in:</ttcol>
<c>1028</c>
<c>IPv4 Router-ID of Local Node</c>
<c>134/---</c>
<c><xref target="RFC5305"></xref>/4.3</c>
<c>1029</c>
<c>IPv6 Router-ID of Local Node</c>
<c>140/---</c>
<c><xref target="RFC6119"></xref>/4.1</c>
<c>1030</c>
<c>IPv4 Router-ID of Remote Node</c>
<c>134/---</c>
<c><xref target="RFC5305"></xref>/4.3</c>
<c>1031</c>
<c>IPv6 Router-ID of Remote Node</c>
<c>140/---</c>
<c><xref target="RFC6119"></xref>/4.1</c>
<c>1088</c>
<c>Administrative group (color)</c>
<c>22/3</c>
<c><xref target="RFC5305"></xref>/3.1</c>
<c>1089</c>
<c>Maximum link bandwidth</c>
<c>22/9</c>
<c><xref target="RFC5305"></xref>/3.3</c>
<c>1090</c>
<c>Max. reservable link bandwidth</c>
<c>22/10</c>
<c><xref target="RFC5305"></xref>/3.5</c>
<c>1091</c>
<c>Unreserved bandwidth</c>
<c>22/11</c>
<c><xref target="RFC5305"></xref>/3.6</c>
<c>1092</c>
<c>TE Default Metric</c>
<c>22/18</c>
<c><xref target="RFC5305"></xref>/3.7</c>
<c>1093</c>
<c>Link Protection Type</c>
<c>22/20</c>
<c><xref target="RFC5307"></xref>/1.2</c>
<c>1094</c>
<c>MPLS Protocol Mask</c>
<c>---</c>
<c><xref target="MPLSPROTOTLV"></xref></c>
<c>1095</c>
<c>Metric</c>
<c>---</c>
<c><xref target="METTLV"></xref></c>
<c>1096</c>
<c>Shared Risk Link Group</c>
<c>---</c>
<c><xref target="SRLGTLV"></xref></c>
<c>1097</c>
<c>Opaque link attribute</c>
<c>---</c>
<c><xref target="OPAQUELINK"></xref></c>
<c>1098</c>
<c>Link Name attribute</c>
<c>---</c>
<c><xref target="LINKNAME"></xref></c>
</texttable>
<section anchor="aux_routerid_link" title="IPv4/IPv6 Router-ID">
<t>The local/remote IPv4/IPv6 Router-ID TLVs are used to
describe auxiliary Router-IDs that the IGP might be
using, e.g., for TE purposes. All auxiliary Router-IDs of
both the local and the remote node MUST be included in the
link attribute of each link NLRI. If there are more than one
auxiliary Router-ID of a given type, then multiple TLVs are
used to encode them.
</t>
</section>
<section anchor="MPLSPROTOTLV" title="MPLS Protocol Mask TLV">
<t>The MPLS Protocol TLV carries a bit mask describing which MPLS
signaling protocols are enabled. The length of this TLV is 1. The
value is a bit array of 8 flags, where each bit represents an MPLS
Protocol capability.</t>
<figure anchor="MPLSPROTO" title="MPLS Protocol TLV">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|R| Reserved |
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The following bits are defined:</t>
<texttable anchor="table_mpls_protocols_tlv"
title="MPLS Protocol Mask TLV Codes">
<ttcol align="center">Bit</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="left">Reference</ttcol>
<c>'L'</c>
<c>Label Distribution Protocol (LDP)</c>
<c><xref target="RFC5036"></xref></c>
<c>'R'</c>
<c>Extension to RSVP for LSP Tunnels (RSVP-TE)</c>
<c><xref target="RFC3209"></xref></c>
<c>'Reserved'</c>
<c>Reserved for future use</c>
<c></c>
</texttable>
</section>
<section anchor="METTLV" title="Metric TLV">
<t>
The IGP Metric TLV carries the metric for this link.
The length of this TLV is variable, depending
on the metric width of the underlying protocol.
IS-IS small metrics have a length of 1 octet
(the two most significant bits are ignored).
OSPF metrics have a length of two octects.
IS-IS wide-metrics have a length of three octets.
</t>
<figure anchor="MET" title="Metric TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IGP Link Metric (variable length) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="SRLGTLV" title="Shared Risk Link Group TLV">
<t>The Shared Risk Link Group (SRLG) TLV carries the Shared Risk
Link Group information (see Section 2.3, "Shared Risk Link Group
Information", of <xref target="RFC4202"></xref>). It contains a data
structure consisting of a (variable) list of SRLG values, where each
element in the list has 4 octets, as shown in <xref
target="SRLG"></xref>. The length of this TLV is 4 * (number of SRLG
values).</t>
<figure anchor="SRLG" title="Shared Risk Link Group TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ............ //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>Note that there is no SRLG TLV in OSPF-TE. In IS-IS the
SRLG information is carried in two different TLVs: the
IPv4 (SRLG) TLV (Type 138) defined in <xref
target="RFC5307"></xref>, and the IPv6 SRLG TLV (Type 139)
defined in <xref target="RFC6119"></xref>. In Link State
NLRI both IPv4 and IPv6 SRLG information are carried in a
single TLV.</t>
</section>
<section anchor="OPAQUELINK"
title="Opaque Link Attribute TLV">
<t>The Opaque link attribute TLV is an envelope that
transparently carries optional link atrribute TLVs advertised by a
router. An originating router shall use this TLV
for encoding information specific to the protocol advertised
in the NLRI header Protocol-ID field or new protocol extensions
to the protocol as advertised in the NLRI header Protocol-ID field
for which there is no protocol neutral
representation in the BGP link-state NLRI.
</t>
<figure anchor="OPAQUELINKTLV"
title="Opaque link attribute format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque link attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="LINKNAME"
title="Link Name TLV">
<t>The Link Name TLV is optional.
The value field identifies the symbolic name of the router link.
This symbolic name can be the FQDN for the link, it can be a
subset of the FQDN, or it can be any string operators want to
use for the link. The use of FQDN or a subset of it is
strongly recommended.
</t>
<t>
The Value field is encoded in 7-bit ASCII. If a user-interface for
configuring or displaying this field permits Unicode characters, that
user-interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in <xref target="RFC3490"/>
to achieve the correct format for transmission or display.
</t>
<t>How a router derives and injects link names
is outside of the scope of this document.
</t>
<figure anchor="optional-link-name-tlv"
title="Link Name format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Link Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
</section>
<section title="Prefix Attribute TLVs">
<t>Prefixes are learned from the IGP topology (IS-IS or OSPF) with a
set of IGP attributes (such as metric, route tags, etc.) that MUST
be reflected into the LINK_STATE attribute. This section describes
the different attributes related to the IPv4/IPv6 prefixes. Prefix
Attributes TLVs SHOULD be used when advertising NLRI types 3 and 4
only. The following attributes TLVs are defined:</t>
<texttable anchor="prefix-attribute_tlv"
title="Prefix Attribute TLVs">
<ttcol align="center">TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="right">Length</ttcol>
<ttcol align="left">Reference</ttcol>
<c>1152</c>
<c>IGP Flags</c>
<c>1</c>
<c><xref target="IGPFLAGS"></xref></c>
<c>1153</c>
<c>Route Tag</c>
<c>4*n</c>
<c><xref target="route_tag"></xref></c>
<c>1154</c>
<c>Extended Tag</c>
<c>8*n</c>
<c><xref target="ext_route_tag"></xref></c>
<c>1155</c>
<c>Prefix Metric</c>
<c>4</c>
<c><xref target="prefix_metric"></xref></c>
<c>1156</c>
<c>OSPF Forwarding Address</c>
<c>4</c>
<c><xref target="ospf_fwd_addr"></xref></c>
<c>1157</c>
<c>Opaque Prefix Attribute</c>
<c>variable</c>
<c><xref target="OPAQUEPREFIX"></xref></c>
</texttable>
<section anchor="IGPFLAGS" title="IGP Flags TLV">
<t>IGP Flags TLV contains IS-IS and OSPF flags and bits originally
assigned to the prefix. The IGP Flags TLV is encoded as
follows:</t>
<figure anchor="IGPFLAGSTLV" title="IGP Flag TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D| Reserved |
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The value field contains bits defined according to the table
below:</t>
<texttable anchor="table_igp_flag_bits_tlv"
title="IGP Flag Bits Definitions">
<ttcol align="center">Bit</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="left">Reference</ttcol>
<c>'D'</c>
<c>IS-IS Up/Down Bit</c>
<c><xref target="RFC5305"></xref></c>
<c>Reserved</c>
<c>Reserved for future use.</c>
<c></c>
</texttable>
</section>
<section anchor="route_tag" title="Route Tag">
<t>Route Tag TLV carries original IGP TAGs (IS-IS <xref
target="RFC5130"></xref> or OSPF) of the prefix and is
encoded as follows:</t>
<figure anchor="IGPROUTETAG" title="IGP Route TAG TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Route Tags (one or more) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>Length is a multiple of 4.</t>
<t>The value field contains one or more Route Tags as learned in the
IGP topology.</t>
</section>
<section anchor="ext_route_tag" title="Extended Route Tag">
<t>Extended Route Tag TLV carries IS-IS Extended Route
TAGs of the prefix <xref target="RFC5130"></xref> and is
encoded as follows:</t>
<figure anchor="IGPEXTROUTETAG"
title="Extended IGP Route TAG TLV format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Extended Route Tag (one or more) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>Length is a multiple of 8.</t>
<t>The 'Extended Route Tag' field contains one or more Extended
Route Tags as learned in the IGP topology.</t>
</section>
<section anchor="prefix_metric" title="Prefix Metric TLV">
<t>Prefix Metric TLV carries the metric of the prefix as
known in the IGP topology <xref target="RFC5305"></xref>.
The attribute is mandatory and can only appear once.</t>
<figure anchor="PREFIXMETRIC" title="Prefix Metric TLV Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>Length is 4.</t>
</section>
<section anchor="ospf_fwd_addr" title="OSPF Forwarding Address TLV">
<t>OSPF Forwarding Address TLV <xref
target="RFC2328"></xref> carries the OSPF forwarding
address as known in the original OSPF
advertisement. Forwarding address can be either IPv4 or
IPv6.</t>
<figure anchor="OSPFFORWADDR"
title="OSPF Forwarding Address TLV Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Forwarding Address (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>Length is 4 for an IPv4 forwarding address an 16 for an IPv6
forwarding address.</t>
</section>
<section anchor="OPAQUEPREFIX"
title="Opaque Prefix Attribute TLV">
<t>The Opaque Prefix attribute TLV is an envelope that
transparently carries optional prefix attribute TLVs advertised by a
router. An originating router shall use this TLV
for encoding information specific to the protocol advertised
in the NLRI header Protocol-ID field or new protocol extensions
to the protocol as advertised in the NLRI header Protocol-ID field
for which there is no protocol neutral
representation in the BGP link-state NLRI.
</t>
<t>The format of the TLV is as follows:</t>
<figure anchor="OPAQUEPREFIXTLV"
title="Opaque Prefix Attribute TLV Format">
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque Prefix Attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>Type is as specified in <xref target="prefix-attribute_tlv"/> and
Length is variable.</t>
</section>
</section>
</section>
<section title="BGP Next Hop Information">
<t>BGP link-state information for both IPv4 and IPv6 networks
can be carried over either an IPv4 BGP session, or an IPv6 BGP
session. If IPv4 BGP session is used, then the next hop in the
MP_REACH_NLRI SHOULD be an IPv4 address. Similarly, if IPv6
BGP session is used, then the next hop in the MP_REACH_NLRI
SHOULD be an IPv6 address. Usually the next hop will be set
to the local end-point address of the BGP session. The next
hop address MUST be encoded as described in <xref
target="RFC4760"></xref>. The length field of the next hop
address will specify the next hop address-family. If the next
hop length is 4, then the next hop is an IPv4 address; if the
next hop length is 16, then it is a global IPv6 address and if
the next hop length is 32, then there is one global IPv6
address followed by a link-local IPv6 address. The link-local
IPv6 address should be used as described in <xref
target="RFC2545"></xref>. For VPN SAFI, as per custom, an 8 byte
route-distinguisher set to all zero is prepended to the next hop.
</t>
<t>The BGP Next Hop attribute is used by each BGP-LS speaker to
validate the NLRI it receives. However, this specification doesn't
mandate any rule regarding the re-write of the BGP Next Hop
attribute.</t>
</section>
<section title="Inter-AS Links">
<t>The main source of TE information is the IGP, which is not
active on inter-AS links. In some cases, the IGP may have
information of inter-AS links (<xref target="RFC5392"></xref>,
<xref target="RFC5316"></xref>). In other cases, for injecting
a non-IGP enabled link into the BGP link-state RIB, an
implementation MUST support configuration of either 'Static'
or 'Direct' links.</t>
</section>
<section title="Router-ID Anchoring Example: ISO Pseudonode">
<t>Encoding of a broadcast LAN in IS-IS provides a good
example of how Router-IDs are encoded. Consider <xref
target="ISISPseudonodes"></xref>. This represents a
Broadcast LAN between a pair of routers. The "real" (=non
pseudonode) routers have both an IPv4 Router-ID and IS-IS
Node-ID. The pseudonode does not have an IPv4
Router-ID. Node1 is the DIS for the LAN. Two
unidirectional links (Node1, Pseudonode 1) and (Pseudonode1,
Node2) are being generated.</t>
<t>The link NRLI of (Node1, Pseudonode1) is encoded as
follows: the IGP Router-ID TLV of the local node
descriptor is 6 octets long containing ISO-ID of Node1,
1920.0000.2001; the IGP Router-ID TLV of the remote node
descriptor is 7 octets long containing the ISO-ID of
Pseudonode1, 1920.0000.2001.02. The BGP-LS attribute of
this link contains one local IPv4 Router-ID TLV (TLV type
1028) containing 192.0.2.1, the IPv4 Router-ID of Node1.
</t>
<t>The link NRLI of (Pseudonode1. Node2) is encoded as
follows: the IGP Router-ID TLV of the local node
descriptor is 7 octets long containing the ISO-ID of
Pseudonode1, 1920.0000.2001.02; the IGP Router-ID TLV of
the remote node descriptor is 6 octets long containing
ISO-ID of Node2, 1920.0000.2002. The BGP-LS attribute of
this link contains one remote IPv4 Router-ID TLV (TLV type
1030) containing 192.0.2.2, the IPv4 Router-ID of Node2.
</t>
<figure anchor="ISISPseudonodes" title="IS-IS Pseudonodes">
<artwork>
+-----------------+ +-----------------+ +-----------------+
| Node1 | | Pseudonode1 | | Node2 |
|1920.0000.2001.00|--->|1920.0000.2001.02|--->|1920.0000.2002.00|
| 192.0.2.1 | | | | 192.0.2.2 |
+-----------------+ +-----------------+ +-----------------+
</artwork>
</figure>
</section>
<section title="Router-ID Anchoring Example: OSPFv2 to IS-IS Migration">
<t>Graceful migration from one IGP to another requires
coordinated operation of both protocols during the migration
period. Such a coordination requires identifying a given
physical link in both IGPs. The IPv4 Router-ID provides that
"glue" which is present in the node descriptors of the OSPF link
NLRI and in the link attribute of the IS-IS link NLRI.
</t>
<t>
Consider a point-to-point link between two routers, A and B,
that initially were OSPFv2-only routers and then IS-IS is
enabled on them. Node A has IPv4 Router-ID and ISO-ID; node B
has IPv4 Router-ID, IPv6 Router-ID and ISO-ID. Each protocol
generates one link NLRI for the link (A, B), both of which are
carried by BGP-LS. The OSPFv2 link NLRI for the link is
encoded with the IPv4 Router-ID of nodes A and B in the local
and remote node descriptors, respectively. The IS-IS link
NLRI for the link is encoded with the ISO-ID of nodes A and B
in the local and remote node descriptors, respectively. In
addition, the BGP-LS attribute of the IS-IS link NLRI contains
the the TLV type 1028 containing the IPv4 Router-ID of node A;
TLV type 1030 containing the IPv4 Router-ID of node B and TLV
type 1031 containing the IPv6 Router-ID of node B. In this
case, by using IPv4 Router-ID, the link (A, B) can be
identified in both IS-IS and OSPF protocol.
</t>
</section>
</section>
<section title="Link to Path Aggregation">
<t>Distribution of all links available in the global Internet is
certainly possible, however not desirable from a scaling and privacy
point of view. Therefore an implementation may support link to path
aggregation. Rather than advertising all specific links of a domain, an
ASBR may advertise an "aggregate link" between a non-adjacent pair of
nodes. The "aggregate link" represents the aggregated set of link
properties between a pair of non-adjacent nodes. The actual methods to
compute the path properties (of bandwidth, metric) are outside the scope
of this document. The decision whether to advertise all specific links
or aggregated links is an operator's policy choice. To highlight the
varying levels of exposure, the following deployment examples are
discussed.</t>
<section title="Example: No Link Aggregation">
<t>Consider <xref target="no-link-aggregation"></xref>. Both AS1 and
AS2 operators want to protect their inter-AS {R1,R3}, {R2, R4} links
using RSVP-FRR LSPs. If R1 wants to compute its link-protection LSP to
R3 it needs to "see" an alternate path to R3. Therefore the AS2
operator exposes its topology. All BGP TE enabled routers in AS1 "see"
the full topology of AS and therefore can compute a backup path. Note
that the decision if the direct link between {R3, R4} or the {R4, R5,
R3) path is used is made by the computing router.</t>
<figure anchor="no-link-aggregation" title="No link aggregation">
<artwork>
AS1 : AS2
:
R1-------R3
| : | \
| : | R5
| : | /
R2-------R4
:
:
</artwork>
</figure>
</section>
<section title="Example: ASBR to ASBR Path Aggregation">
<t>The brief difference between the "no-link aggregation" example and
this example is that no specific link gets exposed. Consider <xref
target="asbr-link-aggregation"></xref>. The only link which gets
advertised by AS2 is an "aggregate" link between R3 and R4. This is
enough to tell AS1 that there is a backup path. However the actual
links being used are hidden from the topology.</t>
<figure anchor="asbr-link-aggregation" title="ASBR link aggregation">
<artwork>
AS1 : AS2
:
R1-------R3
| : |
| : |
| : |
R2-------R4
:
:
</artwork>
</figure>
</section>
<section title="Example: Multi-AS Path Aggregation">
<t>Service providers in control of multiple ASes may even decide to
not expose their internal inter-AS links. Consider <xref
target="multi-as-aggregation"></xref>. AS3 is modeled as a single node
which connects to the border routers of the aggregated domain. <figure
anchor="multi-as-aggregation" title="Multi-AS aggregation">
<artwork>
AS1 : AS2 : AS3
: :
R1-------R3-----
| : : \
| : : vR0
| : : /
R2-------R4-----
: :
: :
</artwork>
</figure></t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document requests a code point from the registry of Address
Family Numbers. As per early allocation procedure this is AFI 16388.</t>
<t>This document requests a code point from the registry of Subsequent
Address Family Numbers. As per early allocation procedure this is SAFI 71.</t>
<t>This document requests a code point from the BGP Path Attributes
registry.</t>
<t>This document requests creation of a new registry for node anchor, link
descriptor and link attribute TLVs. Values 0-255 are reserved. Values
256-65535 will be used for Codepoints. The registry will be initialized as
shown in <xref target="BGPLSCODEPOINTS"/>. Allocations within the registry
will require documentation of the proposed use of the allocated value and
approval by the Designated Expert assigned by the IESG (see <xref
target="RFC5226"></xref>).</t>
<t>Note to RFC Editor: this section may be removed on publication as an
RFC.</t>
</section>
<section anchor="Manageability" title="Manageability Considerations">
<t>This section is structured as recommended in <xref
target="RFC5706"></xref>.</t>
<section anchor="Operational-Considerations"
title="Operational Considerations">
<section anchor="Operations" title="Operations">
<t>Existing BGP operational procedures apply. No new operation
procedures are defined in this document. It is noted that the
NLRI information present in this document purely carries application
level data that has no immediate corresponding forwarding state
impact. As such, any churn in reachability information has different
impact than regular BGP updates which need to change forwarding state
for an entire router. Furthermore it is anticipated that distribution
of this NLRI will be handled by dedicated route-reflectors providing a
level of isolation and fault-containment between different NLRI
types.</t>
</section>
<section anchor="Initial-Setup" title="Installation and Initial Setup">
<t>Configuration parameters defined in <xref
target="Configuration-Management"></xref> SHOULD be initialized to
the following default values: <list style="symbols">
<t>The Link-State NLRI capability is turned off for all
neighbors.</t>
<t>The maximum rate at which Link State NLRIs will be
advertised/withdrawn from neighbors is set to 200 updates per
second.</t>
</list></t>
</section>
<section anchor="Migration-Path" title="Migration Path">
<t>The proposed extension is only activated between BGP peers after
capability negotiation. Moreover, the extensions can be turned
on/off an individual peer basis (see <xref
target="Configuration-Management"></xref>), so the extension can be
gradually rolled out in the network.</t>
</section>
<section anchor="Other-Protocols"
title="Requirements on Other Protocols and Functional Components">
<t>The protocol extension defined in this document does not put new
requirements on other protocols or functional components.</t>
</section>
<section anchor="Network-Operation"
title="Impact on Network Operation">
<t>Frequency of Link-State NLRI updates could interfere with regular
BGP prefix distribution. A network operator MAY use a dedicated
Route-Reflector infrastructure to distribute Link-State NLRIs.</t>
<t>Distribution of Link-State NLRIs SHOULD be limited to a single
admin domain, which can consist of multiple areas within an AS or
multiple ASes.</t>
</section>
<section anchor="Verifying-Correct-Operation"
title="Verifying Correct Operation">
<t>Existing BGP procedures apply. In addition, an implementation
SHOULD allow an operator to: <list style="symbols">
<t>List neighbors with whom the Speaker is exchanging Link-State
NLRIs</t>
</list></t>
</section>
</section>
<section anchor="Management-Considerations"
title="Management Considerations">
<section anchor="Management-Information"
title="Management Information"></section>
<section anchor="Fault-Management" title="Fault Management">
<t>TBD.</t>
</section>
<section anchor="Configuration-Management"
title="Configuration Management">
<t>An implementation SHOULD allow the operator to specify neighbors
to which Link-State NLRIs will be advertised and from which
Link-State NLRIs will be accepted.</t>
<t>An implementation SHOULD allow the operator to specify the
maximum rate at which Link State NLRIs will be advertised/withdrawn
from neighbors</t>
<t>An implementation SHOULD allow the operator to specify the
maximum number of Link State NLRIs stored in router's RIB.</t>
<t>An implementation SHOULD allow the operator to create abstracted
topologies that are advertised to neighbors; Create different
abstractions for different neighbors.</t>
<t>An implementation SHOULD allow the operator to configure a 64-bit
instance ID.</t>
<t>An implementation SHOULD allow the operator to configure a pair
of ASN and BGP-LS identifier per flooding set the node participates
in.</t>
</section>
<section anchor="Accounting-Management" title="Accounting Management">
<t>Not Applicable.</t>
</section>
<section anchor="Performance-Management"
title="Performance Management">
<t>An implementation SHOULD provide the following statistics: <list
style="symbols">
<t>Total number of Link-State NLRI updates sent/received</t>
<t>Number of Link-State NLRI updates sent/received, per
neighbor</t>
<t>Number of errored received Link-State NLRI updates, per
neighbor</t>
<t>Total number of locally originated Link-State NLRIs</t>
</list></t>
</section>
<section anchor="Security-Management" title="Security Management">
<t>An operator SHOULD define ACLs to limit inbound updates as
follows: <list style="symbols">
<t>Drop all updates from Consumer peers</t>
</list></t>
</section>
</section>
</section>
<section anchor="TLVSUMMARY" title="TLV/Sub-TLV Code Points Summary">
<t>This section contains the global table of all TLVs/Sub-TLVs defined in
this document.</t>
<texttable anchor="BGPLSCODEPOINTS"
title="Summary Table of TLV/Sub-TLV Codepoints">
<ttcol align="center">TLV Code Point</ttcol>
<ttcol align="left">Description</ttcol>
<ttcol align="center">IS-IS TLV/ Sub-TLV</ttcol>
<ttcol align="left">Value defined in:</ttcol>
<!-- NLRI TLVs -->
<c>256</c>
<c>Local Node Descriptors</c>
<c>---</c><c>
<xref target="LOCALNODEDESC"></xref></c>
<c>257</c>
<c>Remote Node Descriptors</c>
<c>---</c>
<c><xref target="REMOTENODEDESC"></xref></c>
<c>258</c>
<c>Link Local/Remote Identifiers</c>
<c>22/4</c>
<c><xref target="RFC5307"></xref>/1.1</c>
<c>259</c>
<c>IPv4 interface address</c>
<c>22/6</c>
<c><xref target="RFC5305"></xref>/3.2</c>
<c>260</c>
<c>IPv4 neighbor address</c>
<c>22/8</c>
<c><xref target="RFC5305"></xref>/3.3</c>
<c>261</c>
<c>IPv6 interface address</c>
<c>22/12</c>
<c><xref target="RFC6119"></xref>/4.2</c>
<c>262</c>
<c>IPv6 neighbor address</c>
<c>22/13</c>
<c><xref target="RFC6119"></xref>/4.3</c>
<c>263</c>
<c>Multi-Topology ID</c>
<c>---</c>
<c><xref target="MT-ID"></xref></c>
<c>264</c>
<c>OSPF Route Type</c>
<c>---</c>
<c><xref target="PREFIXDESC"></xref></c>
<c>265</c>
<c>IP Reachability Information</c>
<c>---</c>
<c><xref target="PREFIXDESC"></xref></c>
<!-- NLRI SubTLVs -->
<c>512</c>
<c>Autonomous System</c>
<c>---</c>
<c><xref target="node_desc_tlvs"></xref></c>
<c>513</c>
<c>BGP-LS Identifier</c>
<c>---</c>
<c><xref target="node_desc_tlvs"></xref></c>
<c>514</c>
<c>Area ID</c>
<c>---</c>
<c><xref target="node_desc_tlvs"></xref></c>
<c>515</c>
<c>IGP Router-ID</c>
<c>---</c>
<c><xref target="node_desc_tlvs"></xref></c>
<!-- Link State Attribute TLVs -->
<!-- Node Attributes TLVs -->
<c>1024</c>
<c>Node Flag Bits</c>
<c>---</c>
<c><xref target="NODEFLAGBITS"></xref></c>
<c>1025</c>
<c>Opaque Node Properties</c>
<c>---</c>
<c><xref target="OPAQUENODE"></xref></c>
<c>1026</c>
<c>Node Name</c>
<c>variable</c>
<c><xref target="NODENAME"/></c>
<c>1027</c>
<c>IS-IS Area Identifier</c>
<c>variable</c>
<c><xref target="ISISAREA"/></c>
<c>1028</c>
<c>IPv4 Router-ID of Local Node</c>
<c>134/---</c>
<c><xref target="RFC5305"></xref>/4.3</c>
<c>1029</c>
<c>IPv6 Router-ID of Local Node</c>
<c>140/---</c>
<c><xref target="RFC6119"></xref>/4.1</c>
<c>1030</c>
<c>IPv4 Router-ID of Remote Node</c>
<c>134/---</c>
<c><xref target="RFC5305"></xref>/4.3</c>
<c>1031</c>
<c>IPv6 Router-ID of Remote Node</c>
<c>140/---</c>
<c><xref target="RFC6119"></xref>/4.1</c>
<!-- Link Attribute TLVs -->
<c>1088</c>
<c>Administrative group (color)</c>
<c>22/3</c>
<c><xref target="RFC5305"></xref>/3.1</c>
<c>1089</c>
<c>Maximum link bandwidth</c>
<c>22/9</c>
<c><xref target="RFC5305"></xref>/3.3</c>
<c>1090</c>
<c>Max. reservable link bandwidth</c>
<c>22/10</c>
<c><xref target="RFC5305"></xref>/3.5</c>
<c>1091</c>
<c>Unreserved bandwidth</c>
<c>22/11</c>
<c><xref target="RFC5305"></xref>/3.6</c>
<c>1092</c>
<c>TE Default Metric</c>
<c>22/18</c>
<c><xref target="RFC5305"></xref>/3.7</c>
<c>1093</c>
<c>Link Protection Type</c>
<c>22/20</c>
<c><xref target="RFC5307"></xref>/1.2</c>
<c>1094</c>
<c>MPLS Protocol Mask</c>
<c>---</c>
<c><xref target="MPLSPROTOTLV"></xref></c>
<c>1095</c>
<c>Metric</c>
<c>---</c>
<c><xref target="METTLV"></xref></c>
<c>1096</c>
<c>Shared Risk Link Group</c>
<c>---</c>
<c><xref target="SRLGTLV"></xref></c>
<c>1097</c>
<c>Opaque link attribute</c>
<c>---</c>
<c><xref target="OPAQUELINK"></xref></c>
<c>1098</c>
<c>Link Name attribute</c>
<c>---</c>
<c><xref target="LINKNAME"></xref></c>
<!-- Prefix Attributes TLVs -->
<c>1152</c>
<c>IGP Flags</c>
<c>---</c>
<c><xref target="IGPFLAGS"></xref></c>
<c>1153</c>
<c>Route Tag</c>
<c>---</c>
<c><xref target="RFC5130"></xref></c>
<c>1154</c>
<c>Extended Tag</c>
<c>---</c>
<c><xref target="RFC5130"></xref></c>
<c>1155</c>
<c>Prefix Metric</c>
<c>---</c>
<c><xref target="RFC5305"></xref></c>
<c>1156</c>
<c>OSPF Forwarding Address</c>
<c>---</c>
<c><xref target="RFC2328"></xref></c>
<c>1157</c>
<c>Opaque Prefix Attribute</c>
<c>---</c>
<c><xref target="OPAQUEPREFIX"></xref></c>
</texttable>
</section>
<section anchor="Security" title="Security Considerations">
<t>Procedures and protocol extensions defined in this document
do not affect the BGP security model. See <xref
target="I-D.ietf-karp-routing-tcp-analysis"></xref> for
details.</t>
<t>A BGP Speaker SHOULD NOT accept updates from a Consumer peer.</t>
<t>An operator SHOULD employ a mechanism to protect a BGP Speaker
against DDOS attacks from Consumers.</t>
</section>
<section anchor="Contributors" title="Contributors">
<t>We would like to thank Robert Varga for the significant contribution
he gave to this document.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>We would like to thank Nischal Sheth, Alia Atlas, David Ward, Derek
Yeung, Murtuza Lightwala, John Scudder, Kaliraj Vairavakkalai, Les
Ginsberg, Liem Nguyen, Manish Bhardwaj, Mike Shand, Peter Psenak, Rex
Fernando, Richard Woundy, Steven Luong, Tamas Mondal, Waqas Alam, Vipin
Kumar, Naiming Shen, Balaji Rajagopalan and Yakov Rekhter for their comments.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5130.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6822"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2545.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.1195.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.1918.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2328.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.3209.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.3490.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4202.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4271.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4760.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4915.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5036.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5120.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5301.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5305.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5226.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5307.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6119.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6286.xml"?>
</references>
<references title="Informative References">
<?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-alto-protocol-13.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5392.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5316.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4655.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-karp-routing-tcp-analysis.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4970.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5073.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5152.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5693.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5706.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6549.xml"?>
</references>
</back>
</rfc>
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