One document matched: draft-ietf-ccamp-isis-interas-te-extension-00.txt
Network work group Mach Chen
Internet Draft Renhai Zhang
Expires: August 2008 Huawei Technologies Co.,Ltd
Category: Standards Track Xiaodong Duan
China Mobile
February 3, 2008
ISIS Extensions in Support of Inter-AS Multiprotocol Label Switching
(MPLS) and Generalized MPLS (GMPLS) Traffic Engineering
draft-ietf-ccamp-isis-interas-te-extension-00.txt
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Abstract
This document describes extensions to the ISIS (ISIS) protocol to
support Multiprotocol Label Switching (MPLS) and Generalized MPLS
(GMPLS) Traffic Engineering (TE) for multiple Autonomous Systems
(ASes). It defines ISIS-TE extensions for the flooding of TE
information about inter-AS links which can be used to perform inter-
AS TE path computation.
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No support for flooding TE information from other outside the AS is
proposed or defined in this document.
Conventions used in this document
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 RFC-2119 [RFC2119].
Table of Contents
1. Introduction.................................................2
2. Problem Statement............................................3
2.1. A Note on Non-Objectives................................4
2.2. Per-Domain Path Determination...........................4
2.3. Backward Recursive Path Computation.....................6
3. Extensions to ISIS-TE........................................7
3.1. Inter-AS Reachability TLV...............................8
3.2. TE Router ID............................................9
3.3. Sub-TLV Detail.........................................10
3.3.1. Remote AS Number Sub-TLV..........................10
3.3.2. IPv4 Remote ASBR ID Sub-TLV.......................10
3.3.3. IPv6 Remote ASBR ID Sub-TLV.......................11
3.3.4. IPv4 TE Router ID sub-TLV.........................12
3.3.5. IPv6 TE Router ID sub-TLV.........................12
4. Procedure for Inter-AS TE Links.............................13
4.1. Origin of Proxied TE Information.......................14
5. Security Considerations.....................................14
6. IANA Considerations.........................................15
6.1. Inter-AS Reachability TLV..............................15
6.2. Sub-TLVs for the Inter-AS Reachability TLV.............15
6.3. Sub-TLVs for the IS-IS Router Capability TLV...........16
7. Acknowledgments.............................................16
8. References..................................................16
8.1. Normative References...................................16
8.2. Informative References.................................17
Authors' Addresses.............................................18
Intellectual Property Statement................................18
Disclaimer of Validity.........................................19
Copyright Statement............................................19
1. Introduction
[ISIS-TE] defines extensions to the ISIS protocol [ISIS] to support
intra-area Traffic Engineering (TE). The extensions provide a way of
encoding the TE information for TE-enabled links within the network
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(TE links) and flooding this information within an area. The Extended
IS Reachability TLV and Traffic Engineering Router ID TLV, which are
defined in [ISIS-TE], are used to carry such TE information. The
Extended IS Reachability TLV has several nested sub-TLVs which
describe the TE attributes for a TE link.
[ISIS-TE-V3] and [GMPLS-TE] define similar extensions to ISIS [ISIS]
in support of IPv6 and GMPLS traffic engineering respectively.
Requirements for establishing Multiprotocol Label Switching (MPLS) TE
Label Switched Paths (LSPs) that cross multiple Autonomous Systems
(ASes) are described in [INTER-AS-TE-REQ]. As described in [INTER-AS-
TE-REQ], a method SHOULD provide the ability to compute a path
spanning multiple ASes. So a path computation entity that may be the
head-end Label Switching Router (LSR), an AS Border Router (ASBR), or
a Path Computation Element (PCE [PCE]) needs to know the TE
information not only of the links within an AS, but also of the links
that connect to other ASes.
In this document, a new TLV, which is referred to as the Inter-AS
Reachability TLV, is defined to advertise inter-AS TE information,
three new sub-TLVs are defined for inclusion in the Inter-AS
Reachability TLV to carry the information about the remote AS number
and remote ASBR ID. The sub-TLVs defined in [ISIS-TE], [ISIS-TE-V3]
and other documents for inclusion in the Extended IS Reachability TLV
for describing the TE properties of a TE link are applicable to be
included in the Inter-AS Reachability TLV for describing the TE
properties of an inter-AS TE link as well. And two more new sub-TLVs
are defined for inclusion in the IS-IS Router Capability TLV to carry
the TE Router ID when TE Router ID needs to reach all routers within
an entire ISIS routing domain. The extensions are equally applicable
to IPv4 and IPv6 as identical extensions to [ISIS-TE] and [ISIS-TE-
V3]. The detailed definitions and procedures are discussed in the
following sections.
This document does not propose or define any mechanisms to advertise
any other extra-AS TE information within ISIS. See Section 2.1 for a
full list of non-objectives for this work.
2. Problem Statement
As described in [INTER-AS-TE-REQ], in the case of establishing an
inter-AS TE LSP traversing multiple ASes, the Path message [RFC3209]
may include the following elements in the Explicit Route Object (ERO)
in order to describe the path of the LSP:
- a set of AS numbers as loose hops; and/or
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- a set of LSRs including ASBRs as loose hops.
Two methods for determining inter-AS paths are currently being
discussed. The per-domain method [PD-PATH] determines the path one
domain at a time. The backward recursive method [BRPC] uses
cooperation between PCEs to determine an optimum inter-domain path.
The sections that follow examine how inter-AS TE link information
could be useful in both cases.
2.1. A Note on Non-Objectives
It is important to note that this document does not make any change
to the confidentiality and scaling assumptions surrounding the use of
ASes in the Internet. In particular, this document is conformant to
the requirements set out in [INTER-AS-TE-REQ].
The following features are explicitly excluded:
o There is no attempt to distribute TE information from within one
AS to another AS.
o There is no mechanism proposed to distribute any form of TE
reachability information for destinations outside the AS.
o There is no proposed change to the PCE architecture or usage.
o TE aggregation is not supported or recommended.
o There is no exchange of private information between ASes.
o No ISIS adjacencies are formed on the inter-AS link.
2.2. Per-Domain Path Determination
In the per-domain method of determining an inter-AS path for an MPLS-
TE LSP, when an LSR that is an entry-point to an AS receives a PATH
message from an upstream AS with an ERO containing a next hop that is
an AS number, it needs to find which LSRs (ASBRs) within the local AS
are connected to the downstream AS so that it can compute a TE LSP
segment across the AS to one of those LSRs and forward the PATH
message to it and hence into the next AS. See Figure 1 for an
example :
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R1------R3----R5-----R7------R9-----R11
| | \ | / |
| | \ | ---- |
| | \ | / |
R2------R4----R6 --R8------R10----R12
: :
<-- AS1 -->:<---- AS2 --->:<--- AS3 --->
Figure 1: Inter-AS Reference Model
The figure shows three ASes (AS1, AS2, and AS3) and twelve LSRs (R1
through R12). R3 and R4 are ASBRs in AS1. R5, R6, R7, and R8 are
ASBRs in AS2. R9 and R10 are ASBRs in AS3.
If it is planned to establish an inter-AS TE LSP from R1 to R12, the
AS sequence will be: AS1, AS2, AS3.
Suppose that the Path message enters AS2 from R3. The next hop in the
ERO shows AS3, and R5 must determine a path segment across AS2 to
reach AS3. It has a choice of three exit points from AS2 (R6, R7, and
R8) and it needs to know which of these provide TE connectivity to
AS3, and whether the TE connectivity (for example, available
bandwidth) is adequate for the requested LSP.
Alternatively, if the next hop in the ERO is the entry ASBR for AS3
(say R9), R5 needs to know which of its exit ASBRs has a TE link that
connects to R9. Since there may be multiple ASBRs that are connected
to R9 (both R7 and R8 in this example), R5 also needs to know the TE
properties of the inter-AS TE links so that it can select the correct
exit ASBR.
Once the path message reaches the exit ASBR, any choice of inter-AS
TE link can be made by the ASBR if not already made by entry ASBR
that computed the segment.
More details can be found in the Section 4.0 of [PD-PATH], which
clearly points out why advertising of inter-AS links is desired.
To enable R5 to make the correct choice of exit ASBR the following
information is needed:
o List of all inter-AS TE links for the local AS.
o TE properties of each inter-AS TE link.
o AS number of the neighboring AS connected to by each inter-AS TE
link.
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o Identity (TE Router ID) of the neighboring ASBR connected to by
each inter-AS TE link.
In GMPLS networks further information may also be required to select
the correct TE links as defined in [GMPLS-TE].
The example above shows how this information is needed at the entry
point ASBRs for each AS (or the PCEs that provide computation
services for the ASBRs), but this information is also needed
throughout the local AS if path computation function is fully
distributed among LSRs in the local AS, for example to support LSPs
that have start points (ingress nodes) within the AS.
2.3. Backward Recursive Path Computation
Another scenario using PCE techniques has the same problem. [BRPC]
defines a PCE-based TE LSP computation method (called Backward
Recursive Path Computation) to compute optimal inter-domain
constrained MPLS-TE or GMPLS LSPs. In this path computation method, a
specific set of traversed domains (ASes) are assumed to be selected
before computation starts. Each downstream PCE in domain(i) returns
to its upstream neighbor PCE in domain(i-1) a multipoint-to-point
tree of potential paths. Each tree consists of the set of paths from
all Boundary Nodes located in domain(i) to the destination where each
path satisfies the set of required constraints for the TE LSP
(bandwidth, affinities, etc.).
So a PCE needs to select Boundary Nodes (that is, ASBRs) that provide
connectivity from the upstream AS. In order that the tree of paths
provided by one PCE to its neighbor can be correlated, the identities
of the ASBRs for each path need to be referenced, so the PCE must
know the identities of the ASBRs in the remote AS reached by any
inter-AS TE link, and, in order that it provides only suitable paths
in the tree, the PCE must know the TE properties of the inter-AS TE
links. See the following figure as an example:
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PCE1<------>PCE2<-------->PCE3
/ : :
/ : :
R1------R3----R5-----R7------R9-----R11
| | \ | / |
| | \ | ---- |
| | \ | / |
R2------R4----R6 --R8------R10----R12
: :
<-- AS1 -->:<---- AS2 --->:<--- AS3 --->
Figure 2: BRPC for Inter-AS Reference Model
The figure shows three ASes (AS1, AS2, and AS3), three PCEs(PCE1,
PCE2, and PCE3) and twelve LSRs (R1 through R12). R3 and R4 are ASBRs
in AS1. R5, R6, R7, and R8 are ASBRs in AS2. R9 and R10 are ASBRs in
AS3. PCE1, PCE2, and PCE3 cooperate to perform inter-AS path
computation and are responsible for path segment computation within
their own domains.
If it is planned to establish an inter-AS TE LSP from R1 to R12, the
traversed domains are assumed to be selected: AS1->AS2->AS3, and the
PCE chain is: PCE1->PCE2->PCE3. First, the path computation request
originated from the PCC (R1) is relayed by PCE1 and PCE2 along the
PCE chain to PCE3, then PCE3 begins to compute the path segments from
the entry boundary nodes that provide connection from AS2 to the
destination (R12). But, to provide suitable path segments, PCE3 must
determine which entry boundary nodes provide connectivity to its
upstream neighbor AS (identified by its AS number), and must know the
TE properties of the inter-AS TE links. In the same way, PCE2 also
needs to determine the entry boundary nodes according to its upstream
neighbor AS and the inter-AS TE link capabilities.
Thus, to support Backward Recursive Path Computation the same
information listed in Section 2.2 is required.
3. Extensions to ISIS-TE
Note that this document does not define mechanisms for distribution
of TE information from one AS to another, does not distribute any
form of TE reachability information for destinations outside the AS,
does not change the PCE architecture or usage, does not suggest or
recommend any form of TE aggregation, and does not feed private
information between ASes. See Section 2.1.
In this document, for the advertisement of inter-AS TE links, a new
TLV, which is referred to as the Inter-AS Reachability TLV, is
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defined and three new sub-TLVs are defined for inclusion in the
Inter-AS Reachability TLV to carry the information about the
neighboring AS number and the remote ASBR ID of an inter-AS link. The
sub-TLVs defined in [ISIS-TE], [ISIS-TE-V3] and other documents for
inclusion in the Extended IS Reachability TLV are applicable to be
included in the Inter-AS Reachability TLV for inter-AS TE links
advertisement. And another two new sub-TLVs are defined for inclusion
in the IS-IS Router Capability TLV to carry the TE Router ID when the
TE Router ID is needed to reach all routers within an entire ISIS
routing domain.
3.1. Inter-AS Reachability TLV
The Inter-AS Reachability TLV has type 141 (which needs to be
confirmed by IANA), it contains a data structure consisting of:
7 octets of System ID and Pseudonode Number
3 octets of default metric
1 octet of control information, consisting of:
1 bit of flooding-scope information
1 bit of up/down information
6 bits reserved
1 octet of length of sub-TLVs
0-243 octets of sub-TLVs
where each sub-TLV consists of a sequence of:
1 octet of sub-type
1 octet of length of the value field of the sub-TLV
0-241 octets of value
Compare to the Extended Reachability TLV which is defined in [ISIS-
TE], the Inter-AS Reachability TLV introduces an extra "control
information" field which is consisted of a flooding-scope bit, a
up/down bit and 6 reserved bits.
As the S bit defined in [ISIS-CAP], the flooding-scope bit is used to
control the flooding scope of the Inter-AS Reachability TLV. When the
flooding-scope bit is set to 1, the Inter-AS Reachability TLV MUST be
flooded into the entire ISIS routing domain. If the flooding-scope
bit is set to 0, the Inter-AS Reachability TLV MUST NOT be leaked
between different levels. And this flooding-scope bit MUST NOT be
modified during the TLV leaking. The choice between the use of 0 or 1
is a network-wide policy choice, and configuration control SHOULD be
provided in ASBR implementations that supports the advertisement of
inter-AS TE links.
The semantics of the up/down bit in the Inter-AS Reachability TLV are
identical to the semantics of the up/down bit defined in [ISIS-TE].
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It can be used to facilitate the redistribution of inter-AS TE
information freely between level 1 and level 2. And the up/down bit
MUST be set to 0 when the Inter-AS TE information first injected into
ISIS [ISIS], and the up/dawn bit MUST be set to 1 if the Inter-AS TE
information needs to be advertised from high level to low level.
The sub-TLVs which are defined in [ISIS-TE], [ISIS-TE-V3] and other
documents for describing the TE properties of an TE link are also
applicable to be carried in the Inter-AS Reachability TLV to describe
the TE properties of an Inter-AS TE link. Apart from these sub-TLVs,
three new sub-TLVs are defined for inclusion in the Inter-AS
Reachability TLV in the document:
Sub-TLV type Length Name
------------ ------ ---------------------------
23 4 Remote AS number
24 4 IPv4 Remote ASBR Identifier
25 16 IPv6 Remote ASBR Identifier
The detailed definitions of the three new sub-TLVs are described in
Section 3.3.
3.2. TE Router ID
The IPv4 TE Router ID TLV (type 134) and IPv6 TE Router ID TLV (type
140), which are defined in [ISIS-TE] and [ISIS-TE-V3] respectively,
only have area flooding-scope, when performing inter-AS TE, the TE
Router ID MAY be needed to reach all routers within an entire ISIS
routing domain, and it MUST have the same flooding scope as the
Inter-AS Reachability TLV does.
[ISIS-CAP] defines a generic advertisement mechanism for ISIS which
allows a router to advertise its capabilities within an ISIS area or
an entire ISIS routing domain. And [ISIS-CAP] also points out that TE
Router ID is candidate to be carried in the IS-IS Router Capability
TLV when performing inter-area TE.
This document uses such mechanism for TE Router ID advertisement when
the TE Router ID is needed to reach all routers within an entire ISIS
Routing domain. Two new sub-TLVs are defined for inclusion in the IS-
IS Router Capability TLV to carry the IPv4 and IPv6 TE Router ID
respectively:
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Sub-TLV type Length Name
------------ ------ -----------------
11 4 IPv4 TE Router ID
12 16 IPv6 TE Router ID
The Detailed definitions of the two new sub-TLVs are described in
Section 3.3.
3.3. Sub-TLV Detail
3.3.1. Remote AS Number Sub-TLV
A new sub-TLV, the Remote AS Number sub-TLV is defined for inclusion
in the Inter-AS Reachability TLV when advertising inter-AS links. The
Remote AS Number sub-TLV specifies the AS number of the neighboring
AS to which the advertised link connects.
The Remote AS number sub-TLV is TLV type 23 (which needs to be
confirmed by IANA), and is four octets in length. The format is as
follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Remote AS number field has 4 octets. When only two octets are
used for the AS number, as in current deployments, the left (high-
order) two octets MUST be set to zero. The Remote AS Number Sub-TLV
MUST be included when a router advertises an inter-AS TE link.
3.3.2. IPv4 Remote ASBR ID Sub-TLV
A new sub-TLV, which is referred to as the IPv4 Remote ASBR ID sub-
TLV, is defined for inclusion in the Inter-AS Reachability TLV when
advertising inter-AS links. The IPv4 Remote ASBR ID sub-TLV specifies
the IPv4 identifier of the remote ASBR to which the advertised inter-
AS link connects. This could be any stable and routable IPv4 address
of the remote ASBR. Use of the TE Router ID is RECOMMENDED.
The IPv4 Remote ASBR ID sub-TLV is TLV type 24 (which needs to be
confirmed by IANA), and is four octets in length. The format of the
IPv4 Remote ASBR ID sub-TLV is as follows:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv4 Remote ASBR ID sub-TLV MUST be included if the neighboring
ASBR has an IPv4 address. If the neighboring ASBR does not have an
IPv4 address (not even an IPv4 TE Router ID), the IPv6 Remote ASBR ID
sub-TLV MUST be included instead. An IPv4 Remote ASBR ID sub-TLV and
IPv6 Remote ASBR ID sub-TLV MAY both be present in an Extended IS
Reachability TLV.
3.3.3. IPv6 Remote ASBR ID Sub-TLV
A new sub-TLV, which is referred to as the IPv6 Remote ASBR ID sub-
TLV, is defined for inclusion in the Inter-AS Reachability TLV when
advertising inter-AS links. The IPv6 Remote ASBR ID sub-TLV specifies
the IPv6 identifier of the remote ASBR to which the advertised inter-
AS link connects. This could be any stable and routable IPv6 address
of the remote ASBR. Use of the TE Router ID is RECOMMENDED.
The IPv6 Remote ASBR ID sub-TLV is TLV type 25 (which needs to be
confirmed by IANA), and is sixteen octets in length. The format of
the IPv6 Remote ASBR ID sub-TLV is as follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv6 Remote ASBR ID sub-TLV MUST be included if the neighboring
ASBR has an IPv6 address. If the neighboring ASBR does not have an
IPv6 address, the IPv4 Remote ASBR ID sub-TLV MUST be included
instead. An IPv4 Remote ASBR ID sub-TLV and IPv6 Remote ASBR ID sub-
TLV MAY both be present in an Extended IS Reachability TLV.
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3.3.4. IPv4 TE Router ID sub-TLV
The IPv4 TE Router ID sub-TLV is TLV type 11 (which needs to be
confirmed by IANA), and is four octets in length. The format of the
IPv4 TE Router ID sub-TLV is as follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the TE Router ID is needed to reach all routers within an entire
ISIS routing domain, the IS-IS Router Capability TLV MUST be included
in its LSP. And if an ASBR supports Traffic Engineering for IPv4, the
IPv4 TE Router ID sub-TLV MUST be included if the ASBR has an IPv4 TE
Router ID. If the ASBR does not have an IPv4 TE Router ID, the IPv6
TE Router sub-TLV MUST be included instead. An IPv4 TE Router ID sub-
TLV and IPv6 TE Router ID sub-TLV MAY both be present in an IS-IS
Router Capability TLV.
3.3.5. IPv6 TE Router ID sub-TLV
The IPv6 TE Router ID sub-TLV is TLV type 12 (which needs to be
confirmed by IANA), and is four octets in length. The format of the
IPv6 TE Router ID sub-TLV is as follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the TE Router ID is needed to reach all routers within an entire
ISIS routing domain, the IS-IS Router Capability TLV MUST be included
in its LSP. And if an ASBR supports Traffic Engineering for IPv6, the
IPv6 TE Router ID sub-TLV MUST be included if the ASBR has an IPv6 TE
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Router ID. If the ASBR does not have an IPv6 TE Router ID, the IPv4
TE Router sub-TLV MUST be included instead. An IPv4 TE Router ID sub-
TLV and IPv6 TE Router ID sub-TLV MAY both be present in an IS-IS
Router Capability TLV.
4. Procedure for Inter-AS TE Links
When TE is enabled on an inter-AS link and the link is up, the ASBR
SHOULD advertise this link using the normal procedures for ISIS-TE
[ISIS-TE]. When either the link is down or TE is disabled on the link,
the ASBR SHOULD withdraw the advertisement. When there are changes to
the TE parameters for the link (for example, when the available
bandwidth changes) the ASBR SHOULD re-advertise the link, but the
ASBR MUST take precautions against excessive re-advertisements.
Hellos MUST NOT be exchanged over the inter-AS link, and consequently,
an ISIS adjacency MUST NOT be formed.
The information advertised comes from the ASBR's knowledge of the TE
capabilities of the link, the ASBR's knowledge of the current status
and usage of the link, and configuration at the ASBR of the remote AS
number and remote ASBR TE Router ID.
Legacy routers receiving an advertisement for an inter-AS TE link are
able to ignore it because they do not know the new TLV and sub-TLVs
that are defined in Section 3 in this document. They will continue to
flood the LSP, but will not attempt to use the information received.
In the current operation of ISIS TE the LSRs at each end of a TE link
emit LSAs describing the link. The databases in the LSRs then have
two entries (one locally generated, the other from the peer) that
describe the different 'directions' of the link. This enables CSPF
to do a two-way check on the link when performing path computation
and eliminate it from consideration unless both directions of the
link satisfy the required constraints.
In the case we are considering here (i.e., of a TE link to another AS)
there is, by definition, no IGP peering and hence no bi-directional
TE link information. In order for the CSPF route computation entity
to include the link as a candidate path, we have to find a way to get
LSAs describing its (bidirectional) TE properties into the TE
database.
This is achieved by the ASBR advertising, internally to its AS,
information about both directions of the TE link to the next AS. The
ASBR will normally generate a LSA describing its own side of a link;
here we have it 'proxy' for the ASBR at the edge of the other AS and
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generate an additional LSA that describes that devices 'view' of the
link.
Only some essential TE information for the link needs to be
advertised; i.e., the Interface Address, the Remote AS number and the
Remote ASBR ID of an inter-AS TE link.
Routers or PCEs that are capable of processing advertisements of
inter-AS TE links SHOULD NOT use such links to compute paths that
exit an AS to a remote ASBR and then immediately re-enter the AS
through another TE link. Such paths would constitute extremely rare
occurrences and SHOULD NOT be allowed except as the result of
specific policy configurations at the router or PCE computing the
path.
4.1. Origin of Proxied TE Information
Section 4 describes how to an ASBR advertises TE link information as
a proxy for its neighbor ASBR, but does not describe where this
information comes from.
Although the source of this information is outside the scope of this
document, it is possible that it will be a configuration requirement
at the ASBR, as are other, local, properties of the TE link. Further,
where BGP is used to exchange IP routing information between the
ASBRs, a certain amount of additional local configuration about the
link and the remote ASBR is likely to be available.
We note further that it is possible, and may be operationally
advantageous, to obtain some of the required configuration
information from BGP. Whether and how to utilize these possibilities
is an implementation matter.
5. Security Considerations
The protocol extensions defined in this document are relatively minor
and can be secured within the AS in which they are used by the
existing ISIS security mechanisms.
There is no exchange of information between ASes, and no change to
the ISIS security relationship between the ASes. In particular, since
no ISIS adjacency is formed on the inter-AS links, there is no
requirement for ISIS security between the ASes.
Some of the information included in these new advertisements (e.g.,
the remote AS number and the remote ASBR ID) is obtained manually
from a neighboring administration as part of commercial relationship.
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The source and content of this information should be carefully
checked before it is entered as configuration information at the ASBR
responsible for advertising the inter-AS TE links.
It is worth noting that in the scenario we are considering a Border
Gateway Protocol (BGP) peering may exist between the two ASBRs and
this could be used to detect inconsistencies in configuration. For
example, if a different remote AS number is received in a BGP OPEN
[BGP] from that locally configured into ISIS-TE, as we describe here,
then something is amiss. Note, further, that if BGP is used to
exchange TE information as described in Section 4.1, the inter-AS BGP
session will need to be fully secured.
6. IANA Considerations
IANA is requested to make the following allocations from registries
under its control.
6.1. Inter-AS Reachability TLV
This document defines the following new ISIS TLV type, described in
Section 3.4, that needs to be registered in the ISIS TLV code-point
registry:
Type Description IIH LSP SNP
---- ---------------------- --- --- ---
141 Inter-AS reachability n y n
information
6.2. Sub-TLVs for the Inter-AS Reachability TLV
This document defines the following new sub-TLV types, described in
Sections 3.3.1, 3.3.2 and 3.3.3, of top-level TLV 141 (see section
6.1 above) that need to be registered in the ISIS sub-TLV registry
for TLV 141:
Type Description Length
---- ------------------------------ --------
23 Remote AS number 4
24 IPv4 Remote ASBR Identifier 4
25 IPv6 Remote ASBR Identifier 16
As described above in Section 3.1, the sub-TLVs which are defined in
[ISIS-TE], [ISIS-TE-V3] and other documents for describing the TE
properties of an TE link are applicable to describe an inter-AS TE
link and MAY be included in the Inter-AS Reachability TLV when
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adverting inter-AS TE links. So, these sub-TLVs need to be registered
in the ISIS sub-TLV registry for TLV 141. And in order to simplify
the registration, we suggest using the same registry value as they
are registered in the ISIS sub-TLV registry for TLV 22.
6.3. Sub-TLVs for the IS-IS Router Capability TLV
This document defines the following new sub-TLV types, described in
Sections 3.3.4 and 3.3.5, of top-level TLV 242 (which is defined in
[ISIS-CAP]) that need to be registered in the ISIS sub-TLV registry
for TLV 242:
Type Description Length
---- ------------------------------ --------
11 IPv4 TE Router ID 4
12 IPv6 TE Router ID 16
7. Acknowledgments
The authors would like to thank Adrian Farrel, Jean-Louis Le Roux,
Christian Hopps, and Les Ginsberg for their review and comments on
this document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[ISIS] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[ISIS-TE] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
draft-ietf-isis-te-bis-00.txt, {work in progress}.
[ISIS-TE-V3] Harrison, J., Berger, J., and Bartlett, M., "IPv6
Traffic Engineering in IS-IS", draft-ietf-isis-ipv6-te,
{work in progress}.
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Internet-Draft ISIS extensions for Inter-AS TE February 2008
[ISIS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising
router information", RFC 4971, July 2007.
8.2. Informative References
[INTER-AS-TE-REQ] Zhang and Vasseur, "MPLS Inter-AS Traffic
Engineering Requirements", RFC4216, November 2005.
[PD-PATH] Ayyangar, A., Vasseur, JP., and Zhang, R., "A Per-domain
path computation method for establishing Inter-domain",
draft-ietf-ccamp-inter-domain-pd-path-comp, (work in
progress).
[BRPC] JP. Vasseur, Ed., R. Zhang, N. Bitar, JL. Le Roux, "A Backward
Recursive PCE-based Computation (BRPC) procedure to compute
shortest inter-domain Traffic Engineering Label Switched
Paths ", draft-ietf-pce-brpc, (work in progress)
[PCE] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation
Element (PCE)-Based Architecture", RFC4655, August 2006.
[GMPLS-TE] K.Kompella and Y.Rekhter, "IS-IS Extensions in Support of
Generalized Multi-Protocol Label Switching", RFC 4205,
October 2005.
[BGP] Rekhter, Li, Hares, "A Border Gateway Protocol 4 (BGP-4)",
RFC4271, January 2006
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Authors' Addresses
Mach(Guoyi) Chen
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: mach@huawei.com
Renhai Zhang
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: zhangrenhai@huawei.com
Xiaodong Duan
China Mobile
53A,Xibianmennei Ave,Xunwu District
Beijing, China
Email: duanxiaodong@chinamobile.com
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