One document matched: draft-psenak-ospf-segment-routing-extensions-05.xml
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<rfc category="std" docName="draft-psenak-ospf-segment-routing-extensions-05"
ipr="trust200902">
<front>
<title abbrev="OSPF Extensions for Segment Routing">OSPF Extensions for
Segment Routing</title>
<author fullname="Peter Psenak" initials="P." role="editor"
surname="Psenak">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Apollo Business Center</street>
<street>Mlynske nivy 43</street>
<city>Bratislava</city>
<code>821 09</code>
<country>Slovakia</country>
</postal>
<email>ppsenak@cisco.com</email>
</address>
</author>
<author fullname="Stefano Previdi" initials="S." role="editor"
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="Clarence Filsfils" initials="C." surname="Filsfils">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street/>
<city>Brussels</city>
<region/>
<code/>
<country>Belgium</country>
</postal>
<email>cfilsfil@cisco.com</email>
</address>
</author>
<author fullname="Hannes Gredler" initials="H." surname="Gredler">
<organization>Juniper Networks, Inc.</organization>
<address>
<postal>
<street>1194 N. Mathilda Ave.</street>
<city>Sunnyvale</city>
<code>94089</code>
<region>CA</region>
<country>US</country>
</postal>
<email>hannes@juniper.net</email>
</address>
</author>
<author fullname="Rob Shakir" initials="R." surname="Shakir">
<organization>British Telecom</organization>
<address>
<postal>
<street/>
<city>London</city>
<code/>
<country>UK</country>
</postal>
<email>rob.shakir@bt.com</email>
</address>
</author>
<author fullname="Wim Henderickx" initials="W." surname="Henderickx">
<organization>Alcatel-Lucent</organization>
<address>
<postal>
<street>Copernicuslaan 50</street>
<city>Antwerp</city>
<code>2018</code>
<country>BE</country>
</postal>
<email>wim.henderickx@alcatel-lucent.com</email>
</address>
</author>
<author fullname="Jeff Tantsura" initials="J." surname="Tantsura">
<organization>Ericsson</organization>
<address>
<postal>
<street>300 Holger Way</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>US</country>
</postal>
<email>Jeff.Tantsura@ericsson.com</email>
</address>
</author>
<date day="5" month="June" year="2014"/>
<area>Routing</area>
<workgroup>Open Shortest Path First IGP</workgroup>
<keyword>MPLS</keyword>
<keyword>SID</keyword>
<keyword>IGP</keyword>
<keyword>OSPF</keyword>
<keyword>Label advertisement</keyword>
<keyword>Segment Routing</keyword>
<abstract>
<t>Segment Routing (SR) allows for a flexible definition of end-to-end
paths within IGP topologies by encoding paths as sequences of
topological sub-paths, called "segments". These segments are advertised
by the link-state routing protocols (IS-IS and OSPF).</t>
<t>This draft describes the necessary OSPF extensions that need to be
introduced for Segment Routing.</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>Segment Routing (SR) allows for a flexible definition of end-to-end
paths within IGP topologies by encoding paths as sequences of
topological sub-paths, called "segments". These segments are advertised
by the link-state routing protocols (IS-IS and OSPF). Prefix segments
represent an ecmp-aware shortest-path to a prefix (or a node), as per
the state of the IGP topology. Adjacency segments represent a hop over a
specific adjacency between two nodes in the IGP. A prefix segment is
typically a multi-hop path while an adjacency segment, in most of the
cases, is a one-hop path. SR's control-plane can be applied to both IPv6
and MPLS data-planes, and do not require any additional signaling (other
than the regular IGP). For example, when used in MPLS networks, SR paths
do not require any LDP or RSVP-TE signaling. Still, SR can interoperate
in the presence of LSPs established with RSVP or LDP .</t>
<t>This draft describes the necessary OSPF extensions that need to be
introduced for Segment Routing.</t>
<t>Segment Routing architecture is described in <xref
target="I-D.filsfils-rtgwg-segment-routing"/>.</t>
<t>Segment Routing use cases are described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>.</t>
</section>
<section title="Segment Routing Identifiers">
<t>Segment Routing defines various types of Segment Identifiers (SIDs):
Prefix-SID, Adjacency-SID, LAN Adjacency SID and Binding SID.</t>
<t>For the purpose of the advertisements of various SID values new
Opaque LSAs (defined in <xref target="RFC5250"/>) are defined. These new
LSAs are defined as generic containers that can be used in order to
advertise any additional attributes associated with the prefix or link.
These new Opaque LSAs are complementary to the existing LSAs and are not
aimed to replace any of the existing LSAs.</t>
<section anchor="SIDLABEL" title="SID/Label sub-TLV">
<t>SID/Label sub-TLV appears in multiple TLVs or sub-TLVs defined
later in this document. It is used to advertise SID or label
associated with the prefix or adjacency. SID/Label TLV has following
format:<figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 1</t>
<t>Length: variable, 3 or 4 bytes</t>
<t>SID/Label: if length is set to 3, then the 20 rightmost bits
represent a label. If length is set to 4 then the value represents
a 32 bit SID.</t>
<t>The receiving router MUST ignore SID/Label sub-TLV if the length
is other then 3 or 4.</t>
</list></t>
</section>
</section>
<section anchor="SRCAP" title="Segment Routing Capabilities">
<t>Segment Routing requires some additional capabilities of the router
to be advertised to other routers in the area.</t>
<t>These SR capabilities are advertised in Router Information Opaque LSA
(defined in <xref target="RFC4970"/>).</t>
<section anchor="SRALGO" title="SR-Algorithm TLV">
<t>SR-Algorithm TLV is a TLV of Router Information Opaque LSA (defined
in <xref target="RFC4970"/>).</t>
<t>The SR-Algorithm Sub-TLV is optional, it MAY only appear once
inside the Router Informational Opaque LSA. If the SID/Label Range TLV, as
defined in <xref target="SIDRANGE"/>, is advertised, then SR-Algorithm TLV MUST
also be advertised.</t>
<t>Router may use various algorithms when calculating reachability to
other nodes in area or to prefixes attached to these nodes. Examples
of these algorithms are metric based Shortest Path First (SPF),
various sorts of Constrained SPF, etc. SR-Algorithm TLV allows a
router to advertise algorithms that router is currently using to other
routers in an area. SR-Algorithm TLV has following structure: <figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm n | |
+- -+
| |
+ +
where:</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 8</t>
<t>Length: variable</t>
<t>Algorithm: one octet identifying the algorithm. The following
value has been defined:<list style="hanging">
<t>0: IGP metric based SPT.</t>
</list></t>
</list></t>
<t>RI LSA can be advertised at any of the defined flooding scopes
(link, area, or autonomous system (AS)). For the purpose of the
SR-Algorithm TLV propagation area scope flooding is required.</t>
</section>
<section anchor="SIDRANGE" title="SID/Label Range TLV">
<t>The SID/Label Range TLV is a TLV of Router Information Opaque LSA
(defined in <xref target="RFC4970"/>).</t>
<t>SID/Label Sub-TLV MAY appear multiple times and has following
format:<figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
+ +
where:</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 9</t>
<t>Length: variable</t>
<t>Range Size: 3 octet of the SID/label range</t>
</list></t>
<t>Currently the only supported Sub-TLV is the SID/Label TLV as
defined in <xref target="SIDLABEL"/>. SID/Label advertised in
SID/Label TLV represents the first SID/Label from the advertised
range.</t>
<t>Multiple occurrence of the SID/Label Range TLV MAY be
advertised, in order to advertise multiple ranges. In such case:<list
style="symbols">
<t>The originating router MUST encode each range into a different SID/Label
Range TLV. </t>
<t>The originating router decides in which order the set of SID/Label Range
TLVs are advertised inside Router Information Opaque LSA. The originating router
MUST ensure the order is same after a graceful restart (using checkpointing,
non-volatile storage or any other mechanism) in order to guarantee the same
order before and after graceful restart.</t>
<t> Receiving router must adhere to the order in which the ranges are
advertised when calculating a SID/label from the SID index.</t>
</list></t>
<t>Here follows an example of advertisement of multiple ranges:<figure
suppress-title="true">
<artwork>
The originating router advertises following ranges:
Range 1: [100, 199]
Range 2: [1000, 1099]
Range 3: [500, 599]
The receiving routers concatenate the ranges and build the SRGB
is as follows:
SRGB = [100, 199]
[1000, 1099]
[500, 599]
The indexes span multiple ranges:
index=0 means label 100
...
index 99 means label 199
index 100 means label 1000
index 199 means label 1099
...
index 200 means label 500
...
</artwork>
</figure></t>
<t>RI LSA can be advertised at any of the defined flooding scopes
(link, area, or autonomous system (AS)). For the purpose of the
SR-Capability TLV propagation area scope flooding is required.</t>
</section>
</section>
<section anchor="EXTPXLSA" title="OSPFv2 Extended Prefix Opaque LSA type ">
<t>A new Opaque LSA (defined in <xref target="RFC5250"/>) is defined in
OSPFv2 in order to advertise additional prefix attributes: OSPFv2
Extended Prefix Opaque LSA.</t>
<t>Multiple OSPFv2 Extended Prefix Opaque LSAs can be advertised by a
single router. Flooding scope of the OSPFv2 Extended Prefix Opaque LSA
depends on the content inside the LSA and is in control of the
originating router.</t>
<t>The format of the OSPFv2 Extended Prefix Opaque LSA is as follows:
<figure>
<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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 9, 10, or 11 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque type | Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |</artwork>
</figure></t>
<t>Opaque type used by OSPFv2 Extended Prefix Opaque LSA is 7.</t>
<t>The format of the TLVs within the body of the LSA is the same as the
format used by the Traffic Engineering Extensions to OSPF defined in
<xref target="RFC3630"/>. The LSA payload consists of one or more nested
Type/Length/Value (TLV) triplets. The format of each TLV is:</t>
<figure>
<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... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</artwork>
</figure>
<t>The Length field defines the length of the value portion in octets.
The TLV is padded to 4-octet alignment; padding is not included in the
length field. Nested TLVs are also 32-bit aligned. Unrecognized types
are ignored.</t>
<section title="OSPF Extended Prefix TLV">
<t>The OSPF Extended Prefix TLV is used in order to advertise
additional attributes associated with the prefix. Multiple OSPF
Extended Prefix TLVs MAY be carried in each OSPFv2 Extended Prefix
Opaque LSA, however all prefixes included in the single OSPFv2
Extended Prefix Opaque LSA MUST have the same flooding scope. The
structure of the OSPF Extended Prefix TLV is as follows: <figure>
<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 | Prefix Length | AF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where: </artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 1.</t>
<t>Length: variable</t>
<t>Route type: type of the OSPF route. Supported types are:<figure>
<artwork>
0 - unspecified
1 - intra-area
3 - inter-area
5 - external
7 - NSSA external</artwork>
</figure>If the route type is 0 (unspecified) the information
inside the OSPF External Prefix TLV applies to the prefix
regardless of what route-type it is. This is useful when some
prefix specific attributes are advertised by some external entity,
which is not aware of the route-type associated with the
prefix.</t>
<t>Prefix length: length of the prefix</t>
<t>AF: 0 - IPv4 unicast</t>
<t>Address Prefix: the prefix itself encoded as an even multiple
of 32-bit words, padded with zeroed bits as necessary. This
encoding consumes ((PrefixLength + 31) / 32) 32-bit words. The
default route is represented by a prefix of length 0.</t>
</list></t>
</section>
<section anchor="PREFIXSID" title="Prefix SID Sub-TLV">
<t>The Prefix SID Sub-TLV is a Sub-TLV of the OSPF Extended Prefix
TLV. It MAY appear more than once and has following format: <figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 2.</t>
<t>Length: variable</t>
<t>Flags: 1 octet field. The following flags are defined: <figure
align="center">
<artwork>
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|N|P|M|E|V|L| |
+-+-+-+-+-+-+-+-+
where:</artwork>
</figure><list style="hanging">
<t>N-Flag: Node-SID flag. If set, then the Prefix-SID refers
to the router identified by the prefix. Typically, the N-Flag
is set on Prefix-SIDs attached to a router loopback address.
The N-Flag is set when the Prefix-SID is a Node- SID as
described in <xref
target="I-D.filsfils-rtgwg-segment-routing"/>.</t>
<t>P-Flag: no-PHP flag. If set, then the penultimate hop MUST
NOT pop the Prefix-SID before delivering the packet to the
node that advertised the Prefix-SID.</t>
<t>M-Flag: Mapping Server Flag. If set, the SID is advertised
from the Segment Routing Mapping Server functionality as
described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>.</t>
<t>E-Flag: Explicit-Null Flag. If set, any upstream neighbor
of the Prefix-SID originator MUST replace the Prefix-SID with
a Prefix-SID having an Explicit-NULL value (0 for IPv4) before
forwarding the packet.</t>
<t>The V-Flag: Value/Index Flag. If set, then the Prefix-SID
carries an absolute value. If not set, then the Prefix-SID carries
an index.</t>
<t>The L-Flag: Local/Global Flag. If set, then the value/index
carried by the PrefixSID has local significance. If not set, then
the value/index carried by this subTLV has global significance.</t>
<t>Other bits: MUST be zero when sent and ignored when
received.</t>
</list></t>
<t>MT-ID: Multi-Topology ID (as defined in <xref
target="RFC4915"/>).</t>
<t>Algorithm: one octet identifying the algorithm the Prefix-SID
is associated with as defined in <xref target="SRALGO"/>.</t>
<t>Range size: this field provides the ability to specify a range
of addresses and their associated Prefix SIDs. It represents a
compression scheme to distribute a continuous Prefix and their
continuous, corresponding SID/Label Block. If a single SID is
advertised then the Range Size field MUST be set to one. For range
advertisements > 1, Range Size represents the number of
addresses that need to be mapped into a Prefix-SID.</t>
<t>SID/Index/Label: according to the V and L flags, it contains
either: <list style="hanging">
<t>A 32 bit index defining the offset in the SID/Label space advertised
by this router.</t>
<t>A 24 bit label where the 20 rightmost bits are used for encoding
the label value.</t>
</list></t>
</list></t>
<t>If multiple Prefix-SIDs are advertised for the same prefix, the
receiving router MUST use the first encoded SID and MAY use the
subsequent ones.</t>
<t>When calculating the outgoing label for the prefix, the router MUST
take into account E and P flags advertised by the next-hop router, if
next-hop router advertised the SID for the prefix. This MUST be done
regardless of next-hop router contributing to the best path to the
prefix or not.</t>
<t>P-Flag (no-PHP) MUST be set on the Prefix-SIDs allocated to inter-
area prefixes that are originated by the ABR based on intra-area or
inter-area reachability between areas. In case the inter-area prefix
is generated based on the prefix which is directly attached to the
ABR, P-Flag SHOULD NOT be set</t>
<t>P-Flag (no-PHP) MUST NOT be set on the Prefix-SIDs allocated to
redistributed prefixes, unless the redistributed prefix is directly
attached to ASBR, in which case the P-Flag SHOULD NOT be set.</t>
<t>If the P-flag is not set then any upstream neighbor of the Prefix-SID
originator MUST pop the Prefix-SID. This is equivalent to the penultimate
hop popping mechanism used in the MPLS dataplane. In such case MPLS EXP bits
of the Prefix-SID are not preserved to the ultimate hop (the Prefix-SID
being removed). If the P-flag is unset the received E-flag is ignored.</t>
<t>If the P-flag is set then:<list style="hanging">
<t> If the E-flag is not set then any upstream neighbor of the Prefix-SID
originator MUST keep the Prefix-SID on top of the stack. This is useful when
the originator of the Prefix-SID must stitch the incoming packet into a continuing
MPLS LSP to the final destination. This could occur at an inter-area border router
(prefix propagation from one area to another) or at an inter-domain border router
(prefix propagation from one domain to another).</t>
<t>If the E-flag is set then any upstream neighbor of the Prefix-SID originator
MUST replace the PrefixSID with a Prefix-SID having an Explicit-NULL value. This
is useful, e.g., when the originator of the Prefix-SID is the final destination
for the related prefix and the originator wishes to receive the packet with the
original EXP bits.</t>
</list></t>
<t>When M-Flag is set, P-flag MUST be set and E-bit MUST NOT be set.</t>
<t>Example 1: if the following router addresses (loopback addresses)
need to be mapped into the corresponding Prefix SID indexes: <figure
suppress-title="true">
<artwork>
Router-A: 192.0.2.1/32, Prefix-SID: Index 1
Router-B: 192.0.2.2/32, Prefix-SID: Index 2
Router-C: 192.0.2.3/32, Prefix-SID: Index 3
Router-D: 192.0.2.4/32, Prefix-SID: Index 4
</artwork>
</figure></t>
<t>then the Prefix field in Extended Prefix TLV would be set to
192.0.2.1, Prefix Length would be set to 32, Range Size in Prefix SID
sub-TLV would be 4 and Index value would be set to 1.</t>
<t>Example 2: If the following prefixes need to be mapped into the
corresponding Prefix-SID indexes: <figure suppress-title="true">
<artwork>
10.1.1/24, Prefix-SID: Index 51
10.1.2/24, Prefix-SID: Index 52
10.1.3/24, Prefix-SID: Index 53
10.1.4/24, Prefix-SID: Index 54
10.1.5/24, Prefix-SID: Index 55
10.1.6/24, Prefix-SID: Index 56
10.1.7/24, Prefix-SID: Index 57
</artwork>
</figure></t>
<t>then the Prefix field in Extended Prefix TLV would be set to
10.1.1.0, Prefix Length would be set to 24, Range Size in Prefix SID
sub-TLV would be 7 and Index value would be set to 51.</t>
</section>
<section anchor="SIDBINDING" title="SID/Label Binding sub-TLV">
<t>SID/Label Binding sub-TLV is used to advertise SID/Label mapping
for a path to the prefix. </t>
<t>The SID/Label Binding TLV MAY be originated by any router in an
OSPF domain. The router may advertise a SID/Label binding to a FEC
along with at least a single 'nexthop style' anchor. The protocol
supports more than one 'nexthop style' anchor to be attached to a
SID/Label binding, which results into a simple path description
language. In analogy to RSVP the terminology for this is called an
'Explicit Route Object' (ERO). Since ERO style path notation allows to
anchor SID/label bindings to both link and node IP addresses any
label switched path, can be described. Furthermore also SID/Label
Bindings from external protocols can get easily re-advertised.</t>
<t>The SID/Label Binding TLV may be used for advertising SID/Label
Bindings and their associated Primary and Backup paths. In one single
TLV either a primary ERO Path, a backup ERO Path or both are
advertised. If a router wants to advertise multiple parallel paths
then it can generate several TLVs for the same Prefix/FEC. Each
occurrence of a Binding TLV with respect with a given FEC Prefix has
accumulating and not canceling semantics.</t>
<t>SID/Label Binding sub-TLV is as sub-TLV of the OSPF Extended Prefix
TLV. Multiple SID/Label Binding TLVs can be present in OSPF Extended
Prefix TLV. SID/Label Binding sub-TLV has following format: <figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where: </artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 3</t>
<t>Length: variable</t>
<t>Flags: 1 octet field of following flags:<figure align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|M| |
+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>M-bit - When the bit is set the binding represents the
mirroring context as defined in <xref
target="I-D.minto-rsvp-lsp-egress-fast-protection"/>.</t>
</list></t>
<t>MT-ID: Multi-Topology ID (as defined in <xref
target="RFC4915"/>).</t>
<t>Weight: weight used for load-balancing purposes. The use of the
weight is defined in <xref
target="I-D.filsfils-rtgwg-segment-routing"/>.</t>
<t>Range Size: usage is the same as described in <xref
target="PREFIXSID"/>.</t>
</list></t>
<t>SID/Label Binding TLV currently supports following Sub-TLVs:<list
style="hanging">
<t>SID/Label sub-TLV as described in <xref target="SIDLABEL"/>.
This sub-TLV MUST appear in the SID/Label Binding Sub-TLV and it
MUST only appear once.</t>
<t>ERO Metric sub-TLV as defined in <xref
target="METRICTLV"/>.</t>
<t>ERO sub-TLVs as defined in <xref target="EROTLV"/>.</t>
</list></t>
<!-- begin ERO Metric subTLV -->
<section anchor="METRICTLV" title="ERO Metric sub-TLV">
<t>ERO Metric sub-TLV is a Sub-TLV of the SID/Label Binding TLV.</t>
<t>The ERO Metric sub-TLV carries the cost of an ERO path. It is
used to compare the cost of a given source/destination path. A
router SHOULD advertise the ERO Metric sub-TLV. The cost of the ERO
Metric sub-TLV SHOULD be set to the cumulative IGP or TE path cost
of the advertised ERO. Since manipulation of the Metric field may
attract or distract traffic from and to the advertised segment it
MAY be manually overridden. <figure
title="ERO Metric sub-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 (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>Type: TBD, suggested value 8</t>
<t>Length: 4 bytes</t>
<t>Metric: 4 bytes</t>
</list></t>
</section>
<!-- end ERO metric subTLV -->
<section anchor="EROTLV" title="ERO sub-TLVs">
<t>All 'ERO' information represents an ordered set which describes
the segments of a path. The last ERO sub-TLV describes the segment
closest to the egress point, contrary the first ERO sub-TLV
describes the first segment of a path. If a router extends or
stitches a path it MUST prepend the new segments path information to
the ERO list.</t>
<t>The above similarly applies to backup EROs.</t>
<t>All ERO Sub-TLVs must immediately follow the (SID)/Label
Sub-TLV.</t>
<t>All Backup sub-ERO TLVs must immediately follow last ERO
Sub-TLV.</t>
<section anchor="IPV4ERO" title="IPv4 ERO subTLV">
<t>IPv4 ERO sub-TLV is a Sub-TLV of the SID/Label Binding
sub-TLV.</t>
<t>The IPv4 ERO sub-TLV describes a path segment using IPv4
Address style of encoding. Its semantics have been borrowed from
<xref target="RFC3209"/>. <figure title="IPv4 ERO sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>Type: TBD, suggested value 4</t>
<t>Length: 8 bytes</t>
<t>Flags: 1 octet field of following flags: <figure
align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>L-bit - If the L bit is set, then the value of the
attribute is 'loose.' Otherwise, the value of the
attribute is 'strict.'</t>
</list></t>
<t>IPv4 Address - the address of the explicit route hop.</t>
</list></t>
</section>
<section anchor="UNNERO" title="Unnumbered Interface ID ERO sub-TLV">
<t>Unnumbered Interface ID ERO sub-TLV is a Sub-TLV of the
SID/Label Binding sub-TLV.</t>
<t>The appearance and semantics of the 'Unnumbered Interface ID'
have been borrowed from <xref target="RFC3477"/>.</t>
<t>The Unnumbered Interface-ID ERO sub-TLV describes a path
segment that spans over an unnumbered interface. Unnumbered
interfaces are referenced using the interface index. Interface
indices are assigned local to the router and therefore not unique
within a domain. All elements in an ERO path need to be unique
within a domain and hence need to be disambiguated using a domain
unique Router-ID. <figure
title="Unnumbered Interface ID ERO sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 5</t>
<t>Length: 12 bytes</t>
<t>Flags: 1 octet field of following flags:<figure
align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where: </artwork>
</figure><list style="hanging">
<t>L-bit - If the L bit is set, then the value of the
attribute is 'loose.' Otherwise, the value of the
attribute is 'strict.'</t>
</list></t>
<t>Router-ID: Router-ID of the next-hop.</t>
<t>Interface ID: is the identifier assigned to the link by the
router specified by the Router-ID.</t>
</list></t>
</section>
<section anchor="IPV4BERO" title="IPv4 Backup ERO sub-TLV">
<t>IPv4 Prefix Backup ERO sub-TLV is a Sub-TLV of the SID/Label
Binding sub-TLV.</t>
<t>The IPv4 Backup ERO sub-TLV describes a path segment using IPv4
Address style of encoding. Its semantics have been borrowed from
<xref target="RFC3209"/>. <figure
title="IPv4 Backup ERO sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>Type: TBD, suggested value 6</t>
<t>Length: 8 bytes</t>
<t>Flags: 1 octet field of following flags: <figure
align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>L-bit - If the L bit is set, then the value of the
attribute is 'loose.' Otherwise, the value of the
attribute is 'strict.'</t>
</list></t>
<t>IPv4 Address - the address of the explicit route hop.</t>
</list></t>
</section>
<section anchor="UNNBERO"
title="Unnumbered Interface ID Backup ERO sub-TLV">
<t>Unnumbered Interface ID Backup -sub-TLV is a sub-TLV of the
SID/Label Binding sub-TLV.</t>
<t>The appearance and semantics of the 'Unnumbered Interface ID'
have been borrowed from <xref target="RFC3477"/>.</t>
<t>The Unnumbered Interface-ID ERO sub-TLV describes a path
segment that spans over an unnumbered interface. Unnumbered
interfaces are referenced using the interface index. Interface
indices are assigned local to the router and therefore not unique
within a domain. All elements in an ERO path need to be unique
within a domain and hence need to be disambiguated using a domain
unique Router-ID. <figure
title="Unnumbered Interface ID Backup ERO sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>Type: TBD, suggested value 7</t>
<t>Length: 12 bytes</t>
<t>Flags: 1 octet field of following flags: <figure
align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
</artwork>
</figure> where: <list style="hanging">
<t>L-bit - If the L bit is set, then the value of the
attribute is 'loose.' Otherwise, the value of the
attribute is 'strict.'</t>
</list></t>
<t>Router-ID: Router-ID of the next-hop.</t>
<t>Interface ID: is the identifier assigned to the link by the
router specified by the Router-ID.</t>
</list></t>
</section>
</section>
</section>
</section>
<section anchor="ADJSID" title="Adjacency Segment Identifier (Adj-SID)">
<t>An Adjacency Segment Identifier (Adj-SID) represents a router
adjacency in Segment Routing. At the current stage of Segment Routing
architecture it is assumed that the Adj-SID value has local significance
(to the router).</t>
<section title="OSPFv2 Extended Link Opaque LSA ">
<t>A new Opaque LSA (defined in <xref target="RFC5250"/> is defined in
OSPFv2 in order to advertise additional link attributes: the OSPFv2
Extended Link Opaque LSA.</t>
<t>The OSPFv2 Extended Link Opaque LSA has an area flooding scope.
Multiple OSPFv2 Extended Link Opaque LSAs can be advertised by a
single router in an area.</t>
<t>The format of the OSPFv2 Extended Link Opaque LSA is as follows:
<figure>
<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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque type | Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |</artwork>
</figure></t>
<t>Opaque type used by OSPFv2 Extended Link Opaque LSA is 8.</t>
<t>The format of the TLVs within the body of LSA is the same as the
format used by the Traffic Engineering Extensions to OSPF defined in
<xref target="RFC3630"/>. The LSA payload consists of one or more
nested Type/Length/Value (TLV) triplets. The format of each TLV
is:</t>
<figure>
<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... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</artwork>
</figure>
<t>The Length field defines the length of the value portion in octets.
The TLV is padded to 4-octet alignment; padding is not included in the
length field. Nested TLVs are also 32-bit aligned. Unrecognized types
are ignored.</t>
</section>
<section title="OSPFv2 Extended Link TLV">
<t>OSPFv2 Extended Link TLV is used in order to advertise various
attributes of the link. It describes a single link and is constructed
of a set of Sub-TLVs. There are no ordering requirements for the
Sub-TLVs. Only one Extended Link TLV SHALL be carried in each Extended
Link Opaque LSA, allowing for fine granularity changes in the
topology.</t>
<t>The Extended Link TLV has following format:<figure>
<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-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:</artwork>
</figure><list>
<t>Type is 1.</t>
<t>Length is variable.</t>
<t>Link-Type: as defined in section A.4.2 of <xref
target="RFC2328"/>.</t>
<t>Link-ID: as defined in section A.4.2 of <xref
target="RFC2328"/>.</t>
<t>Link Data: as defined in section A.4.2 of <xref
target="RFC2328"/>.</t>
</list></t>
</section>
<section anchor="ADJSIDSUBTLV" title="Adj-SID sub-TLV">
<t>Adj-SID is an optional Sub-TLV of the Extended Link TLV. It MAY
appear multiple times in Extended Link TLV. Examples where more than
one Adj-SID may be used per neighbor are described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>. The structure
of the Adj-SID Sub-TLV is as follows: <figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
where:</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 2.</t>
<t>Length: variable.</t>
<t>Flags. 1 octet field of following flags:<figure align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B|V|L|S| |
+-+-+-+-+-+-+-+-+
where:</artwork>
</figure><list style="hanging">
<t>B-Flag: Backup-flag: set if the Adj-SID refer to an
adjacency being protected (e.g.: using IPFRR or MPLS-FRR) as
described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>.</t>
<t>The V-Flag: Value/Index Flag. If set, then the Prefix-SID
carries an absolute value. If not set, then the Prefix-SID carries
an index.</t>
<t>The L-Flag: Local/Global Flag. If set, then the value/index
carried by the PrefixSID has local significance. If not set, then
the value/index carried by this subTLV has global significance.</t>
<t>The S-Flag. Set Flag. When set, the S-Flag indicates that the
Adj-SID refers to a set of adjacencies (and therefore MAY be assigned
to other adjacencies as well).</t>
<t>Other bits: MUST be zero when originated and ignored when
received.</t>
</list></t>
<t>MT-ID: Multi-Topology ID (as defined in <xref
target="RFC4915"/>.</t>
<t>Weight: weight used for load-balancing purposes. The use of the
weight is defined in <xref
target="I-D.filsfils-rtgwg-segment-routing"/>.</t>
<t>SID/Index/Label: according to the V and L flags, it contains
either: <list style="hanging">
<t>A 32 bit index defining the offset in the SID/Label space advertised
by this router.</t>
<t>A 24 bit label where the 20 rightmost bits are used for encoding
the label value.</t>
</list></t>
</list></t>
<t>A SR capable router MAY allocate an Adj-SID for each of its
adjacencies and set the B-Flag when the adjacency is protected by a
FRR mechanism (IP or MPLS) as described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>.</t>
</section>
<section anchor="LANADJSIDSUBTLV" title="LAN Adj-SID Sub-TLV">
<t>LAN Adj-SID is an optional Sub-TLV of the Extended Link TLV. It MAY
appear multiple times in Extended Link TLV. It is used to advertise
SID/Label for adjacency to non-DR node on broadcast or NBMA network.
<figure>
<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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
where:</artwork>
</figure><list style="hanging">
<t>Type: TBD, suggested value 3.</t>
<t>Length: variable.</t>
<t>Flags. 1 octet field of following flags:<figure align="center">
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B|V|L|S| |
+-+-+-+-+-+-+-+-+
where:</artwork>
</figure><list style="hanging">
<t>B-Flag: Backup-flag: set if the LAN-Adj-SID refer to an
adjacency being protected (e.g.: using IPFRR or MPLS-FRR) as
described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>.</t>
<t>The V-Flag: Value/Index Flag. If set, then the Prefix-SID
carries an absolute value. If not set, then the Prefix-SID carries
an index.</t>
<t> The L-Flag: Local/Global Flag. If set, then the value/index
carried by the PrefixSID has local significance. If not set, then
the value/index carried by this subTLV has global significance.</t>
<t>The S-Flag. Set Flag. When set, the S-Flag indicates that the
Adj-SID refers to a set of adjacencies (and therefore MAY be assigned
to other adjacencies as well).</t>
<t>Other bits: MUST be zero when originated and ignored when
received.</t>
</list></t>
<t>MT-ID: Multi-Topology ID (as defined in <xref
target="RFC4915"/>.</t>
<t>Weight: weight used for load-balancing purposes. The use of the
weight is defined in <xref
target="I-D.filsfils-rtgwg-segment-routing"/>.</t>
<t>SID/Index/Label: according to the V and L flags, it contains
either: <list style="hanging">
<t>A 32 bit index defining the offset in the SID/Label space advertised
by this router.</t>
<t>A 24 bit label where the 20 rightmost bits are used for encoding
the label value.</t>
</list></t>
</list></t>
</section>
</section>
<section title="Elements of Procedure">
<section title="Intra-area Segment routing in OSPFv2 ">
<t>The OSPFv2 node that supports segment routing MAY advertise Prefix-
SIDs for any prefix that it is advertising reachability for (e.g.
loopback IP address) as described in <xref target="PREFIXSID"/>.</t>
<t>If multiple routers advertise Prefix-SID for the same prefix, then
the Prefix-SID MUST be the same. This is required in order to allow
traffic load-balancing if multiple equal cost paths to the destination
exist in the network.</t>
<t>Prefix-SID can also be advertised by the SR Mapping Servers (as
described in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>). The Mapping
Server advertise Prefix-SID for remote prefixes that exist in the
network. Multiple Mapping Servers can advertise Prefix-SID for the
same prefix, in which case the same Prefix-SID MUST be advertised by
all of them. Flooding scope of the OSPF Extended Prefix Opaque LSA
that is generated by the SR Mapping Server could be either area scope
or autonomous system scope and is decided based on the configuration
of the SR Mapping Server.</t>
</section>
<section title="Inter-area Segment routing in OSPFv2">
<t>In order to support SR in a multi-area environment, OSPFv2 must
propagate Prefix-SID information between areas. The following
procedure is used in order to propagate Prefix SIDs between areas.</t>
<t>When an OSPF ABR advertises a Type-3 Summary LSA from an intra-area
prefix to all its connected areas, it will also originate an Extended
Prefix Opaque LSA, as described in <xref target="EXTPXLSA"/>. The
flooding scope of the Extended Prefix Opaque LSA type will be set to
area-scope. The route-type in OSPF Extended Prefix TLV is set to
inter-area. The Prefix-SID Sub-TLV will be included in this LSA and
the Prefix-SID value will be set as follows: <list style="hanging">
<t>The ABR will look at its best path to the prefix in the source
area and find out the advertising router associated with its best
path to that prefix.</t>
<t>If no Prefix-SID was advertised for the prefix in the source
area by the router that contributes to the best path to the
prefix, then the ABR will use the Prefix-SID advertised by any
other router (e.g.: a Prefix-SID coming from an SR Mapping Server
as defined in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>) when
propagating Prefix-SID for the prefix to other areas.</t>
</list></t>
<t>When an OSPF ABR advertises Type-3 Summary LSAs from an inter-area
route to all its connected areas it will also originate an Extended
Prefix Opaque LSA, as described in <xref target="EXTPXLSA"/>. The
flooding scope of the Extended Prefix Opaque LSA type will be set to
area-scope. The route-type in OSPF Extended Prefix TLV is set to
inter-area. The Prefix-SID Sub-TLV will be included in this LSA and
the Prefix-SID will be set as follows: <list style="hanging">
<t>The ABR will look at its best path to the prefix in the source
area and find out the advertising router associated with its best
path to that prefix.</t>
<t>The ABR will then look if such router advertised a Prefix-SID
for the prefix and use it when advertising the Prefix-SID to other
connected areas.</t>
<t>If no Prefix-SID was advertised for the prefix in the source
area by the ABR that contributes to the best path to the prefix,
the originating ABR will use the Prefix-SID advertised by any
other router (e.g.: a Prefix-SID coming from an SR Mapping Server
as defined in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>) when
propagating Prefix-SID for the prefix to other areas.</t>
</list></t>
</section>
<section title="SID for External Prefixes">
<t>Type-5 LSAs are flooded domain wide. When an ASBR, which supports
SR, generates Type-5 LSAs, it should also originate Extended Prefix
Opaque LSAs, as described in <xref target="EXTPXLSA"/>. The flooding
scope of the Extended Prefix Opaque LSA type is set to AS-scope. The
route-type in OSPF Extended Prefix TLV is set to external. Prefix-SID
Sub-TLV is included in this LSA and the Prefix-SID value will be set
to the SID that has been reserved for that prefix.</t>
<t>When a NSSA ASBR translates Type-7 LSAs into Type-5 LSAs, it should
also advertise the Prefix-SID for the prefix. The NSSA ABR determines
its best path to the prefix advertised in the translated Type-7 LSA
and finds the advertising router associated with such path. If such
advertising router has advertised a Prefix-SID for the prefix, then
the NSSA ASBR uses it when advertising the Prefix-SID for the Type-5
prefix. Otherwise the Prefix-SID advertised by any other router will
be used (e.g.: a Prefix-SID coming from an SR Mapping Server as
defined in <xref
target="I-D.filsfils-rtgwg-segment-routing-use-cases"/>).</t>
</section>
<section title="Advertisement of Adj-SID">
<t>The Adjacency Segment Routing Identifier (Adj-SID) is advertised
using the Adj-SID Sub-TLV as described in <xref target="ADJSID"/>.</t>
<section title="Advertisement of Adj-SID on Point-to-Point Links">
<t>Adj-SID MAY be advertised for any adjacency on p2p link that is
in a state 2-Way or higher. If the adjacency on a p2p link
transitions from the FULL state, then the Adj-SID for that adjacency
MAY be removed from the area. If the adjacency transitions to a
state lower then 2-Way, then the Adj-SID MUST be removed from the
area.</t>
</section>
<section title="Adjacency SID on Broadcast or NBMA Interfaces">
<t>Broadcast or NBMA networks in OSPF are represented by a star
topology where the Designated Router (DR) is the central point all
other routers on the broadcast or NBMA network connect to. As a
result, routers on the broadcast or NBMA network advertise only
their adjacency to DR and BDR. Routers that are neither DR nor BDR
do not form and do not advertise adjacencies between them. They,
however, maintain a 2-Way adjacency state between them.</t>
<t>When Segment Routing is used, each router on the broadcast or
NBMA network MAY advertise the Adj-SID for its adjacency to DR using
Adj-SID Sub-TLV as described in <xref target="ADJSIDSUBTLV"/>.</t>
<t>SR capable router MAY also advertise Adj-SID for other neighbors
(e.g. BDR, DR-OTHER) on broadcast or NBMA network using the LAN
ADJ-SID Sub-TLV as described in section 5.1.1.2. <xref
target="LANADJSIDSUBTLV"/>.</t>
</section>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This specification updates two existing OSPF registries.</t>
<t>Opaque Link-State Advertisements (LSA) Option Types:</t>
<t>o suggested value 7 - OSPFv2 Extended Prefix Opaque LSA</t>
<t>o suggested value 8 - OSPFv2 Extended Link Opaque LSA</t>
<t>OSPF Router Information (RI) TLVs:</t>
<t>o suggested value 8 - SR-Algorithm TLV</t>
<t>o suggested value 9 - SID/Label Range TLV</t>
<t>This specification also creates four new registries:</t>
<t>- OSPF Extended Prefix LSA TLVs and sub-TLVs</t>
<t>- OSPF Extended Link LSA TLVs and sub-TLVs</t>
<section anchor="EPLTLVREG" title="OSPF Extend Prefix LSA TLV Registry">
<t>The OSPF Extend Prefix LSA TLV registry will define top-level TLVs
for Extended Prefix LSAs and should be placed in the existing OSPF IANA
registry. New values can be allocated via IETF Consensus or IESG
Approval.</t>
<t>Following initial values are allocated:</t>
<t>o 0 - Reserved</t>
<t>o 1 - OSPF Extended Prefix TLV</t>
<t>Types in the range 32768-32023 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by
RFCs.</t>
<t> Types in the range 32023-65535 are not to be assigned at this
time. Before any assignments can be made in this range, there
MUST be a Standards Track RFC that specifies IANA Considerations
that covers the range being assigned.</t>
</section>
<section anchor="EPLSTLVREG" title="OSPF Extend Prefix LSA sub-TLV Registry">
<t>The OSPF Extended Prefix sub-TLV registry will define will define
sub-TLVs at any level of nesting for Extended Prefix LSAs and should be
placed in the existing OSPF IANA registry. New values can be allocated
via IETF Consensus or IESG Approval.</t>
<t>Following initial values are allocated:</t>
<t>o 0 - Reserved</t>
<t>o 1 - SID/Label sub-TLV</t>
<t>o 2 - Prefix SID sub-TLV</t>
<t>o 3 - SID/Label Binding sub-TLV</t>
<t>o 4 - IPv4 ERO sub-TLV</t>
<t>o 5 - Unnumbered Interface ID ERO sub-TLV</t>
<t>o 6 - IPv4 Backup ERO sub-TLV</t>
<t>o 7 - Unnumbered Interface ID Backup ERO sub-TLV</t>
<t>o 8 - ERO Metric sub-TLV</t>
<t>Types in the range 32768-32023 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by
RFCs.</t>
<t>Types in the range 32023-65535 are not to be assigned at this
time. Before any assignments can be made in this range, there
MUST be a Standards Track RFC that specifies IANA Considerations
that covers the range being assigned.</t>
</section>
<section anchor="ELLTLVREG" title="OSPF Extend Link LSA TLV Registry">
<t>The OSPF Extend Link LSA TLV registry will define top-level TLVs for
Extended Link LSAs and should be placed in the existing OSPF IANA
registry. New values can be allocated via IETF Consensus or IESG
Approval.</t>
<t>Following initial values are allocated:</t>
<t>o 0 - Reserved</t>
<t>o 1 - OSPFv2 Extended Link TLV</t>
<t>Types in the range 32768-32023 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by
RFCs.</t>
<t>Types in the range 32023-65535 are not to be assigned at this
time. Before any assignments can be made in this range, there
MUST be a Standards Track RFC that specifies IANA Considerations
that covers the range being assigned.</t>
</section>
<section anchor="ELLSTLVREG" title="OSPF Extend Link LSA sub-TLV Registry">
<t>The OSPF Extended Link LSA sub-TLV registry will define will define
sub-TLVs at any level of nesting for Extended Link LSAs and should be
placed in the existing OSPF IANA registry. New values can be allocated
via IETF Consensus or IESG Approval.</t>
<t>Following initial values are allocated:</t>
<t>o 1 - SID/Label sub-TLV</t>
<t>o 2 - Adj-SID sub-TLV</t>
<t>o 3 - LAN Adj-SID/Label Sub-TLV</t>
<t>Types in the range 32768-32023 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by
RFCs.</t>
<t>Types in the range 32023-65535 are not to be assigned at this
time. Before any assignments can be made in this range, there
MUST be a Standards Track RFC that specifies IANA Considerations
that covers the range being assigned.</t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>In general, new LSAs defined in this document are subject to the same
security concerns as those described in <xref target="RFC2328"/>.
Additionally, implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard OSPF failures.</t>
</section>
<section anchor="Contributors" title="Contributors">
<t>The following people gave a substantial contribution to the content
of this document: Ahmed Bashandy, Martin Horneffer, Bruno Decraene,
Stephane Litkowski, Igor Milojevic, Rob Shakir and Saku Ytti.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>We would like to thank Anton Smirnov for his contribution.</t>
<t>Many thanks to Yakov Rekhter, John Drake and Shraddha Hedge for their
contribution on earlier incarnations of the "Binding / MPLS Label TLV"
in <xref target="I-D.gredler-ospf-label-advertisement"/>.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3209.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3477.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3630.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5250.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2328.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4970.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4915.xml"?>
<?rfc ?>
</references>
<references title="Informative References">
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-filsfils-rtgwg-segment-routing-01.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-filsfils-rtgwg-segment-routing-use-cases-02.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-minto-rsvp-lsp-egress-fast-protection-03.xml"?>
<?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-gredler-ospf-label-advertisement-03.xml"?>
</references>
</back>
</rfc>
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