Internet DRAFT - draft-gredler-isis-label-advertisement
draft-gredler-isis-label-advertisement
IS-IS for IP Internets H. Gredler, Ed.
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track S. Amante
Expires: November 22, 2013 Level 3 Communications, Inc.
T. Scholl
Amazon
L. Jalil
Verizon
May 21, 2013
Advertising MPLS labels in IS-IS
draft-gredler-isis-label-advertisement-03
Abstract
Historically MPLS label distribution was driven by protocols like
LDP, RSVP and LBGP. All of those protocols are session oriented. In
order to obtain a label binding for a given destination FEC from a
given router one needs first to establish an LDP/RSVP/LBGP session
with that router.
Advertising MPLS labels in IGPs
[I-D.gredler-rtgwg-igp-label-advertisement] describes several use
cases where utilizing the flooding machinery of link-state protocols
for MPLS label distribution allows to obtain the binding without
requiring to establish an LDP/RSVP/LBGP session with that router.
This document describes the protocol extension to distribute MPLS
label bindings using the IS-IS protocol.
Requirements Language
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].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 22, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Motivation, Rationale and Applicability . . . . . . . . . . . 4
2.1. Issue: Bi-directionality semantics . . . . . . . . . . . . 5
2.2. Issue: IP path semantics . . . . . . . . . . . . . . . . . 5
2.3. Issue: Lack of 'path' notion . . . . . . . . . . . . . . . 5
2.4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 6
3. MPLS label TLV . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. subTLV support . . . . . . . . . . . . . . . . . . . . . . 7
3.3. IPv4 Prefix ERO subTLV . . . . . . . . . . . . . . . . . . 7
3.4. IPv6 Prefix ERO subTLV . . . . . . . . . . . . . . . . . . 8
3.5. Unnumbered Interface ID ERO subTLV . . . . . . . . . . . . 9
3.6. IPv4 Prefix Bypass ERO subTLV . . . . . . . . . . . . . . 10
3.7. IPv6 Prefix Bypass ERO subTLV . . . . . . . . . . . . . . 10
3.8. Unnumbered Interface ID Bypass ERO subTLV . . . . . . . . 11
3.9. Prefix ERO and Prefix Bypass ERO subTLV path semantics . . 12
3.10. All Router Block subTLV . . . . . . . . . . . . . . . . . 12
3.11. All Router ID IPv4 Map subTLV . . . . . . . . . . . . . . 14
3.12. All Router ID IPv6 Map subTLV . . . . . . . . . . . . . . 15
4. Advertising Label Examples . . . . . . . . . . . . . . . . . . 15
4.1. Sample Topology . . . . . . . . . . . . . . . . . . . . . 15
4.1.1. Transport IP addresses and Router-IDs . . . . . . . . 16
4.1.2. Link IP addresses . . . . . . . . . . . . . . . . . . 16
4.2. One-hop LSP to an adjacent Router . . . . . . . . . . . . 17
4.3. One-hop LSP to an adjacent Router using a specific link . 17
4.4. Advertisement of Fast Re-Route LSP for One-Hop LSP . . . . 17
4.5. Advertisement of an RSVP LSP . . . . . . . . . . . . . . . 18
4.6. Advertisement of an LDP LSP . . . . . . . . . . . . . . . 18
4.7. Interarea advertisement of diverse paths . . . . . . . . . 18
4.8. Advertisement of SPT labels using 'All Router Block'
TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.9. Expansion of an 'All Router Block' subTLV . . . . . . . . 20
5. Inter Area Protocol Procedures . . . . . . . . . . . . . . . . 21
5.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 21
5.2. Data plane operations . . . . . . . . . . . . . . . . . . 21
5.3. Control plane operations . . . . . . . . . . . . . . . . . 21
5.3.1. MPLS Label operations . . . . . . . . . . . . . . . . 21
5.3.2. MPLS Label Block operations . . . . . . . . . . . . . 22
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
MPLS label allocations are predominantly distributed by using the LDP
[RFC5036], RSVP [RFC5151] or labeled BGP [RFC3107] protocol. All of
those protocols have in common that they are session oriented, which
means that in order to obtain label binding for a given destination
FEC from a given router one needs first to establish a direct control
plane (LDP/RSVP/LBGP) session with that router.
There are a couple of practical use cases
[I-D.gredler-rtgwg-igp-label-advertisement] where the consumer of a
MPLS label binding may not be adjacent to the router that performs
the binding. Bringing up an explicit session using the existing
label distribution protocols between the non-adjacent router that
binds the label and the router that acts as a consumer of this
binding is the existing remedy for this dilemma.
This document describes an IS-IS protocol extension which allows
routers to advertise MPLS label bindings within and beyond an IGP
domain, and controlling inter-area distribution.
2. Motivation, Rationale and Applicability
One possible way of distributing MPLS labels using IS-IS has been
described in Segment Routing
[I-D.previdi-filsfils-isis-segment-routing]. The authors propose to
re-use the IS-Reach TLVs (22, 23, 222) and Extended IP Prefix TLVs
(135, 236) for carrying the label information. While retrofitting
existing protocol machinery for new purposes is generally a good
thing, Segment Routing [I-D.previdi-filsfils-isis-segment-routing]
falls short of addressing some use-cases defined in
[I-D.gredler-rtgwg-igp-label-advertisement].
The dominant issue around re-using IS-Reach TLVs and the extended IP
Prefix TLVs is that both family of TLVs have existing protocol
semantics, which might not be well suitable to advertising MPLS label
switched paths in a generic fashion. These are specifically:
o Bi-directionality semantics
o IP path semantics
o Lack of 'path' notion
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2.1. Issue: Bi-directionality semantics
'Bi-directionality semantics', affects the complexity around
advertisement of unidirectional LSPs. Label advertisement of per-
link labels or 'Adj-SIDs' [I-D.previdi-filsfils-isis-segment-routing]
is done using IS-reach TLVs. Usually implementations need to have an
adjacency in 'Up' state prior to advertising this adjacency as IS-
reach TLV in its Link State PDUs (LSPs). In order to advertise e.g.
one-hop MPLS LSP in a given link an implementation first needs to
have an adjacency, which only transitions to 'Up' state after passing
the 3-way check. This implies bi-directionality. If an
implementation wants to advertise per-link LSPs to e.g. outside the
IGP domain then it would need to fake-up an adjacency. Changing
existing IGP Adjacency code to support such cases defeats the purpose
of re-using existing functionality as there is not much common
functionality to be shared.
2.2. Issue: IP path semantics
LSPs pointing to a Node are advertised as 'Node-SIDs'
[I-D.previdi-filsfils-isis-segment-routing] using the family of
extended IP Reach TLVs. That means that in order to advertise a MPLS
LSP, one is inheriting the semantics of advertising an IP path.
Consider router A has got existing MPLS LSPs to its entire one-hop
neighborhood and is re-advertising those MPLS LSPs using IP
reachability semantics. Now we have two exact matching IP
advertisements. One from the owning router (router B) which
advertises its stable transport loopback address and another one from
router A re-advertising a MPLS LSP path to router B. Existing routing
software may get confused now as the 'stable transport' address shows
up from multiple places in the network and more worse the IP
forwarding path for control-plane protocols may get mingled with the
MPLS data plane.
2.3. Issue: Lack of 'path' notion
Both IS-Reach TLVs and IP Prefix Reachability TLVs have a limited
semantics describing MPLS label-switched paths in the sense of a
'path'. Both encoding formats allow to specify a pointer to some
specific router, but not to describe a MPLS label switched path
containing all of its path segments.
[I-D.previdi-filsfils-isis-segment-routing] allows to define
'Forwarding Adjacencies' as per [RFC4206]. The way to describe a
path of a given forwarding adjacency is to carry a list of "Segment
IDs". That implies that nodes which do not yet participate in
'Segment routing' or are outside of a 'Segment routing' domain can
not be expressed using those path semantics.
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A protocol for advertising MPLS label switched paths, should be
generic enough to express paths sourced by existing MPLS LSPs, such
that ingress routers can flexibly combine them according to
application needs.
2.4. Motivation
IGP advertisement of MPLS label switched paths requires a new set of
protocol semantics (path paradigm), which hardly can be expressed
using the existing IS-IS protocol. This document describes IS-IS
protocol extensions which allows generic advertisement of MPLS label
bindings in IS-IS.
The Protocol extensions described in this document are equally
applicable to IPv4 and IPv6 carried over MPLS. Furthermore the
proposed use of distributing MPLS Labels using IGP prototocols
adheres to the architectural principles laid out in [RFC3031].
3. MPLS label TLV
The MPLS Label TLV may be originated by any Traffic Engineering
[RFC5305] capable router in an IS-IS domain. The router may
advertise a single label binding or a block of label bindings. For
single label binding advertisement a router needs to provide at least
a single 'nexthop style' anchor. The protocol supports more than one
'nexthop style' anchor to be attached to a 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 label bindings to to
both link and node IP addresses any label switched path, can be
described. Furthermore also Label Bindings from other protocols can
get easily re-advertised.
Due to the limited size of subTLV space (See [RFC5311] section 4.5
for details), The MPLS Label TLV has cumulative rather than canceling
semantics. If a router originates more than one MPLS Label TLV with
the same Label value, then the subTLVs of the second, third, etc.
TLV are accumulated. Since some subTLVs represent an ordered set
(e.g. ERO subTLVs) allocation and ordering of TLV space inside
particular IS-IS LSP fragment is significant and needs to be tracked.
The MPLS Label TLV has type 149 and has the following format:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|R|R|R| MPLS Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MPLS TLV format
o 4 bits of flags, consisting of:
* 1 bit of up/down information (U bit)
* 3 bits are reserved for future use
o 20 bits of MPLS label information
o 0-252 octets of sub-TLVs, where each sub-TLV consists of a
sequence of:
* 1 octet of sub-TLV type
* 1 octet of length of the value field of the sub-TLV
* 0-250 octets of value
3.1. Flags
Flags
Up/Down Bit: A router may flood MPLS label information across
level boundaries. In order to prevent flooding loops, a router
will Set the Up/Down (U-Bit) when propagating from Level 2 down to
Level 1. This is done as per the procedures for IP Prefixes lined
out in [RFC5302].
3.2. subTLV support
An originating router MAY want to attach one or more subTLVs to the
MPLS label TLV. SubTLVs presence is inferred from the length of the
MPLS Label TLV. If the MPLS Label TLV Length field is > 3 octets
then one or more subTLVs may be present.
3.3. IPv4 Prefix ERO subTLV
The IPv4 ERO subTLV (Type 1) describes a path segment using IPv4
Prefix style of encoding. Its appearance and semantics have been
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borrowed from Section 4.3.3.2 [RFC3209].
The 'Prefix Length' field contains the length of the prefix in bits.
Only the most significant octets of the prefix are encoded. 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.
The 'L' bit in the subTLV is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.'
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Prefix Length | IPv4 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix (continued, variable-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: IPv4 Prefix ERO subTLV format
3.4. IPv6 Prefix ERO subTLV
The IPv6 ERO subTLV (Type 2) describes a path segment using IPv6
Prefix style of encoding. Its appearance and semantics have been
borrowed from Section 4.3.3.3 [RFC3209].
The 'Prefix Length' field contains the length of the prefix in bits.
Only the most significant octets of the prefix are encoded. 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, ...., 16 octets for prefix length 113 up to 128.
The 'L' bit in the subTLV is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.'
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Prefix Length | IPv6 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued, variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IPv6 Prefix ERO subTLV format
3.5. Unnumbered Interface ID ERO subTLV
The appearance and semantics of the 'Unnumbered Interface ID' have
been borrowed from Section 4 [RFC3477].
The Unnumbered Interface-ID ERO subTLV (Type 9) 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.
The 'Router-ID' field contains the router ID of the router which has
assigned the 'Interface ID' field. Its purpose is to disambiguate
the 'Interface ID' field from other routers in the domain.
IS-IS supports two Router-ID formats:
o (TLV 134, 32-Bit format) [RFC5305]
o (TLV 140, 128-Bit format) [RFC6119]
The actual Router-ID format gets derived from the 'Length' field.
o For 32-Bit Router-ID width the subTLV length is set to 8 octets.
o For 128-Bit Router-ID width the subTLV length is set to 20 octets.
The 'Interface ID' is the identifier assigned to the link by the
router specified by the router ID.
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The 'L' bit in the subTLV is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.'
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Router ID (32 or 128 bits) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Unnumbered Interface ID ERO subTLV format
3.6. IPv4 Prefix Bypass ERO subTLV
The IPv4 Bypass ERO subTLV (Type 3) describes a Bypass LSP path
segment using IPv4 Prefix style of encoding. Its appearance and
semantics have been borrowed from Section 4.3.3.2 [RFC3209].
The 'Prefix Length' field contains the length of the prefix in bits.
Only the most significant octets of the prefix are encoded, 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.
The 'L' bit in the subTLV is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.'
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Prefix Length | IPv4 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix (continued, variable-length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IPv4 Prefix Bypass ERO subTLV format
3.7. IPv6 Prefix Bypass ERO subTLV
The IPv6 ERO subTLV (Type 4) describes a Bypass LSP path segment
using IPv6 Prefix style of encoding. Its appearance and semantics
have been borrowed from Section 4.3.3.3 [RFC3209].
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The 'Prefix Length' field contains the length of the prefix in bits.
Only the most significant octets of the prefix are encoded, 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, ...., 16 octets for prefix length 113 up to 128.
The 'L' bit in the subTLV is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.'
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Prefix Length | IPv6 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Prefix (continued, variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: IPv6 Prefix Bypass ERO subTLV format
3.8. Unnumbered Interface ID Bypass ERO subTLV
The appearance and semantics of the 'Unnumbered Interface ID' have
been borrowed from Section 4 [RFC3477].
The Unnumbered Interface-ID Bypass ERO subTLV (Type 10) describes a
Bypass LSP 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.
The 'Router-ID' field contains the router ID of the router which has
assigned the 'Interface ID' field. Its purpose is to disambiguate
the 'Interface ID' field from other routers in the domain.
IS-IS supports two Router-ID formats:
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o (TLV 134, 32-Bit format) [RFC5305]
o (TLV 140, 128-Bit format) [RFC6119]
The actual Router-ID format gets derived from the 'Length' field.
o For 32-Bit Router-ID width the subTLV length is set to 8 octets.
o For 128-Bit Router-ID width the subTLV length is set to 20 octets.
The 'Interface ID' is the identifier assigned to the link by the
router specified by the router ID.
The 'L' bit in the subTLV is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.'
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Router ID (32 or 128 bits) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Unnumbered Interface ID Bypass ERO subTLV format
3.9. Prefix ERO and Prefix Bypass ERO subTLV path semantics
All 'Prefix ERO' and 'Prefix Bypass ERO' information represents an
ordered set which describes the segments of a label-switched path.
The last Prefix ERO subTLV describes the segment closest to the
egress point of the LSP. Contrary the first Prefix ERO subTLV
describes the first segment of a label switched path. If a router
extends or stitches a label switched path it MUST prepend the new
segments path information to the Prefix ERO list. The same ordering
applies for the Bypass ERO labels. An implementation SHOULD first
encode all primary path EROs followed by the bypass EROs.
3.10. All Router Block subTLV
The 'All Router Block' subTLV (Type 6) denominates the label block
size of an MPLS Label advertisement and its semantics to connect to
all routers in a given IS-IS domain using a local assigned [RFC3031]
label range. Note that the actual mapping of a router within the
label range is done using the subTLVs described in Section 3.11 and
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Section 3.12. Since generation of an 'All Router ID IPv4 Map' or
'All Router ID IPv6 Map' subTLV is a local policy decision, it might
be the case that connectivity is provided not to 'All' but rather a
subset of 'All' routers. Keeping policy decisions aside, for
simplicity reasons, assume that All Routers in a domain do generate
either the 'All Router ID IPv4 Map' or 'All Router ID IPv6 Map'
subTLVs and therefore all routers desire construction of a Label
switched path from every source router in the network. The basic
concept of using label blocks to provide connectivity to a set of
routers has been borrowed from [RFC4761] which allows to advertise
labels from multiple end-points using a single control-plane message.
The difference to [RFC4761] is that rather than advertising where a
particular packet came from (=source semantics), destination
semantics (where a particular packet will be going to) is advertised.
Along with each label block a router advertises one for more 'IDs'.
The 'ID' must be unique within a given domain. The 'ID' serves as
ordinal to determine the actual label value inside the set of all
advertised label ranges of a given router. A receiving router uses
the ordinal to determine the actual label value in order to construct
forwarding state to a particular destination router. The 'ID' is
separately advertised using the subTLVs described in Section 3.11 and
Section 3.12.
The ability to advertise more than one label block eases operational
procedures for increasing the number of supported routers within a
domain. For example consider a given domain has got support for <M>
routers and runs out of ID space. It simply advertises one more
label block to cover additional ordinals outside the range of the
first label block. An example of label-block expansion is described
in more detail in Section 4.9
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block Size | Algo | Topology-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: All Router Block subTLV format
The 'Block Size' value contains the size of the label advertisement.
The 'value determines the amount of reachable router endpoints within
a given Label block. It MUST contain a value greater or equal than
two. Note that the label base is inferred from the Label Value in
the carrying MPLS Label TLV. For example if a router wants to
advertise a label range of 5000-5099 then it would need to generate a
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MPLS Label TLV with a Label value of 5000 and a Block Size of 100.
The 'Algo' value denominates the path computation algorithm in order
to calculate the forwarding topology. The basic SPF algorithm has an
assigned 'Algo' code point of zero. The purpose of the 'Algo' field
is to extend the notion of Label Block Signaling to arbitrary
algorithms like for example 'MRT'
([I-D.ietf-rtgwg-mrt-frr-architecture]. Advertised Label Blocks with
an unknown, unsupported or non-configured algorithm MUST be silently
ignored.
The 'Reserved' bits are for future use. They should be zero on
transmission and ignored on receipt.
The 'Topology-ID' field contains the Multi Topology ID ([RFC5120])
for which the advertised Label Block does apply. The basic IPv4
unicast Topology has an assigned 'Topology-ID' code point of zero.
The basic IPv6 unicast Topology has an assigned 'Topology=ID' code
point of 2. Advertised Label Blocks with an unknown, unsupported or
non-configured Topology-ID MUST be silently ignored.
A MPLS Label TLV containing the 'All Router Block' subTLV MUST only
contain the 'All Router IPv4 Map' subTLV (Section 3.11) or the 'All
Router IPv6 Map' subTLV (Section 3.12).
3.11. All Router ID IPv4 Map subTLV
The 'All Router ID IPv4 Map' TLV (Type 7) maps an 'ID' to a given
stable transport IPv4 address. Its purpose is to associate a given
transport IPv4 IP address to the ordinal inside a label range as
described in Section 3.10.
A router MAY advertise more than one 'ID' to 'IPv4 address' mapping
pair, in case it has more than one stable transport IPv4 address.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: All Router ID IPv4 Map subTLV format
The 'IPv4 address' contains stable IPv4 transport address of a given
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router.
The 'ID' contains the ordinal value of an advertising router inside
the set of all advertised label blocks of a given router.
3.12. All Router ID IPv6 Map subTLV
The 'All Router ID IPv6 Map' TLV (Type 8) maps an 'ID' to a given
stable transport IPv6 address. Its purpose is to associate a given
transport IPv6 IP address to the ordinal inside a label range as
described in Section 3.10.
A router MAY advertise more than one 'ID' to 'IPv6 address' mapping
pair, in case it has more than one stable transport IPv6 address.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: All Router ID IPv6 Map subTLV format
The 'IPv6 address' contains the stable IPv6 transport address of a
given router.
The 'ID' contains the ordinal value of an advertising router inside
the set of all advertised label blocks of a given router.
4. Advertising Label Examples
4.1. Sample Topology
The following topology (Figure 11) and IP addresses shall be used
throughout the Label advertisement examples.
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AS1 : AS 2
:
: :
Level 1 : Level 2 :
: :
: :
+-----+ +-----+-IP3--1-IP4--+-----+ :
| R1 +-IP1--1-IP2--+ R2 | | R3 | :
+--+--+ +--+--+-IP5--3-IP6--+--+--+-IP15-IP16-
| | | : \
IP9 IP7 IP13 : \
| | | : +--+--+
1 1 1 : | R7 |
| | | : +--+--+
IP10 IP8 IP14 : /
| | | : /
+--+--+ +--+--+ +--+--+-IP17-IP18-
| R4 +-IP19-2-IP20-+ R5 |-IP11-2-IP12-| R6 | :
+-----+ +-----+ +-----+ :
: :
: :
: :
Figure 11: Sample Topology
4.1.1. Transport IP addresses and Router-IDs
o R1: 192.168.1.1
o R2: 192.168.1.2
o R3: 192.168.1.3
o R4: 192.168.1.4
o R5: 192.168.1.5
o R6: 192.168.1.6
o R7: 192.168.1.7
4.1.2. Link IP addresses
o R1 to R2 link: 10.0.0.1, 10.0.0.2
o R1 to R4 link: 10.0.0.9, 10.0.0.10
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o R2 to R3 link #1: 10.0.0.3, 10.0.0.4
o R2 to R3 link #2: 10.0.0.5, 10.0.0.6
o R2 to R5 link: 10.0.0.7, 10.0.0.8
o R3 to R6 link: 10.0.0.13, 10.0.0.14
o R3 to R7 link: 10.0.0.15, 10.0.0.16
o R4 to R5 link: 10.0.0.19, 10.0.0.20
o R5 to R6 link: 10.0.0.11, 10.0.0.12
o R6 to R7 link: 10.0.0.17, 10.0.0.18
The IGP link metrics are displayed in the middle of the link. All of
them are assumed to be bi-directional.
4.2. One-hop LSP to an adjacent Router
If R1 would advertise a label <N> bound to a one-hop LSP from R1 to
R2 it would encode as follows:
TLV 149: MPLS label <N>, Flags {}:
IPv4 Prefix ERO subTLV: 192.168.1.2/32, Strict
4.3. One-hop LSP to an adjacent Router using a specific link
If R2 would advertise a label <N> bound to a one-hop LSP from R2 to
R3, using the link #2 it would encode as follows
TLV 149: MPLS label <N>, Flags {}:
IPv4 Prefix ERO subTLV: 10.0.0.6/32, Strict
4.4. Advertisement of Fast Re-Route LSP for One-Hop LSP
R2 may advertise a one-hop LSP from R2 to R3, along with a Link
Protection Bypass for the directly adjacent links between those two
nodes. The Link Protection Bypass would use the path: {R2, R5, R6,
R3}. R2 would encode both the primary LSP and Link Protection Bypass
LSP as follows:
TLV 149: MPLS label <N>, Flags {}:
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IPv4 Prefix ERO subTLV: 192.168.1.3/32, Strict
IPv4 Prefix Bypass ERO subTLV: 192.168.1.5/32, Strict
IPv4 Prefix Bypass ERO subTLV: 192.168.1.6/32, Strict
IPv4 Prefix Bypass ERO subTLV: 192.168.1.3/32, Strict
4.5. Advertisement of an RSVP LSP
Consider a RSVP LSP name "R2-to-R6" traversing (R2 to R3 using link
#1, R6):
If R2 would advertise a label <N> bound to the RSVP LSP named
'R2-to-R6', it would encode as follows
TLV 149: MPLS label <N>, Flags {}:
IPv4 Prefix ERO subTLV: 10.0.0.4/32, Strict
IPv4 Prefix ERO subTLV: 192.168.1.6/32, Strict
4.6. Advertisement of an LDP LSP
Consider R2 that creates a LDP label binding for FEC 172.16.0.0/12
using label <N>.
If R2 would re-advertise this binding in IS-IS it would encode as
follows
TLV 149: MPLS label <N>, Flags {}:
IPv4 Prefix ERO subTLV: 172.16.0.0/12, Loose
4.7. Interarea advertisement of diverse paths
Consider two R2->R6 paths: {R2, R3, R6} and {R2, R5, R6}
Consider two R5->R3 paths: {R5, R2, R3} and {R5, R6, R3}
R2 encodes its two paths to R6 as follows:
TLV 149: MPLS label <N1>, Flags {}:
IPv4 Prefix ERO subTLV: 192.168.1.3, Strict
IPv4 Prefix ERO subTLV: 192.168.1.6, Strict
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TLV 149: MPLS label <N2>, Flags {}:
IPv4 Prefix ERO subTLV: 192.168.1.5, Strict
IPv4 Prefix ERO subTLV: 192.168.1.6, Strict
R5 encodes its two paths to R3 as follows:
TLV 149: MPLS label <N1>, Flags {}:
IPv4 Prefix ERO subTLV: 192.168.1.2, Strict
IPv4 Prefix ERO subTLV: 192.168.1.3, Strict
TLV 149: MPLS label <N2>, Flags {}:
IPv4 Prefix ERO subTLV: 192.168.1.6, Strict
IPv4 Prefix ERO subTLV: 192.168.1.3, Strict
A receiving L1 router does see now all 4 paths and may decide to
load-balance across all or a subset of them.
4.8. Advertisement of SPT labels using 'All Router Block' TLV
All routers within a given area MUST advertise their Label Blocks
along with an 'ID'.
If R2 would advertise a label block <N1> with a size of 10, declaring
SPT label forwarding support to all routers within a given domain, it
would encode as follows:
TLV 149: MPLS Label <N1>, Flags {}:
All Router Block subTLV: Block Size 10, Algo 0, Topology 0
All Router ID IPv4 Map subTLV: ID 2, 192.168.1.2
If R3 would advertise a label block <N2> with a size of 10, declaring
SPT label forwarding support to all routers within a given domain, it
would encode as follows:
TLV 149, MPLS Label <N2>, Flags {}:
All Router Block subTLV: Block Size 10, Algo 0, Topology 0
All Router ID IPv4 Map subTLV: ID 3, 192.168.1.3
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If R5 would advertise a label block <N3> with a size of 10, declaring
SPT label forwarding support to all routers within a given domain, it
would encode as follows:
TLV 149, MPLS Label <N3>, Flags {}:
All Router Block subTLV: Block Size 10, Algo 0, Topology 0
All Router ID IPv4 Map subTLV: ID 5, 192.168.1.5
If R6 would advertise a label block <N4> with a size of 10, declaring
SPT label forwarding support to all routers within a given domain, it
would encode as follows:
TLV 149, MPLS Label <N4>, Flags {}:
All Router Block subTLV: Block Size 10, Algo 0, Topology 0
All Router ID IPv4 Map subTLV: ID 6, 192.168.1.6
Consider now R2 constructing a SPT label for R6. R2s SPT to R6 is
{R2, IP4, R3, R6}. R2 first determines if its downstream router (R3)
has advertised a label-block. Since R3 has advertised a label block
'N2' and it has received R6 'ID' of 6 it will be picking the 6th
label value inside the advertised range of its downstream neighbor.
Specifically R2 MUST be program a MPLS SWAP for its own label range
Label(N1+6) to Label(N2+6), NH 10.0.0.4 into its MPLS transit RIB.
Furthermore R2 MAY program a MPLS PUSH operation for IP 192.168.1.6
to Label (N2+6), NH 10.0.0.4 into its IPv4 tunnel RIB.
Next walk down to R3, which is the next router on the SPT tree
towards R6. R3s SPT to R6 is {R3, R6}. R3 determines if its
downstream router (R6) has advertised a label-block. Since R6 has
advertised a label block 'N4' and it has received R6 'ID' of 6 it
will be picking the 6th label value inside the advertised range of
its downstream neighbor. Since R3 is the penultimate router to R6 it
MUST program a MPLS POP for its own label range Label(N2+6) NH
10.0.0.14 into its MPLS transit RIB. Furthermore R3 MAY program a
MPLS NOP for IP 192.168.1.6, NH 10.0.0.14 into its IPv4 tunnel RIB.
4.9. Expansion of an 'All Router Block' subTLV
All routers within a given area MUST advertise their Label Blocks
along with an 'ID'. Now assume that the initial label block size
assignment is too small to support all routers which generate an
ordinal within an IGP domain. Consider the seven routers in
Figure 11, and assume that R7 advertises a new ID '15' using an 'All
Router ID Map' subTLV. ID '15' is outside of the range of '10' as
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per the previous example in Section 4.8. Now all the routers in an
IGP domain need to advertise one more label block in order to map the
ID '15' to an actual label value.
All routers would advertise in addition to their label block <N> with
a size of 10, a second label block <N2> with a size sufficient enough
that the new ordinal can get covered. In this example the same block
size 10 is used also for the second label block. For example router
R2 would advertise the following label bindings.
TLV 149: MPLS Label <N1>, Flags {}:
All Router Block subTLV: Block Size 10, Algo 0, Topology 0
All Router ID IPv4 Map subTLV: ID 2, 192.168.1.2
TLV 149: MPLS Label <N2>, Flags {}:
All Router Block subTLV: Block Size 10, Algo 0, Topology 0
Now the upstream router can map the new ID of R7 to an actual label
value, as ID '15' corresponds to the 5th label inside the second
Label block.
5. Inter Area Protocol Procedures
5.1. Applicability
Propagation of a MPLS LSP across a level boundary is a local policy
decision.
5.2. Data plane operations
If local policy dictates that a given L1L2 router needs to re-
advertise a MPLS LSPs from one Level to another then it MUST allocate
a new label and program its label forwarding table to connect the new
label to the path in the respective other level. Depending on how to
reach the re-advertised LSP, this is typically done using a MPLS
'SWAP' or 'SWAP/PUSH' data plane operation.
5.3. Control plane operations
5.3.1. MPLS Label operations
If local policy dictates that a given L1L2 router re-advertises a
MPLS LSPs into another Level then it MUST prepend its "Traffic-
Engineering-ID" as a loose hop in the Prefix ERO subTLV list. If the
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LSP is propagated from a higher Level to a lower Level then the
'Down' bit MUST be set.
5.3.2. MPLS Label Block operations
If local policy dictates that a given L1L2 router advertises its 'All
Router Block' into another Level, then it also MUST re-advertise all
known 'ID' ordinals (again gated by policy) to the respective other
Level. Without knowledge of all 'ID's in the network no router is
able to construct SPT label switched paths. If a Label Block and its
ID mappings are propagated from a higher Level to a lower Level then
the 'Down' bit MUST be set.
6. Acknowledgements
Many thanks to Yakov Rekhter and John Drake for their useful
comments.
7. IANA Considerations
This documents request allocation for the following TLVs and subTLVs.
+-----+--------+----------------------+------+---------+------------+
| PDU | TLV | subTLV | Type | subType | #Occurence |
+-----+--------+----------------------+------+---------+------------+
| LSP | MPLS | | 149 | | >=0 |
| | Label | | | | |
| | | IPv4 Prefix ERO | | 1 | >=0 |
| | | IPv6 Prefix ERO | | 2 | >=0 |
| | | Unnumbered Interface | | 9 | >=0 |
| | | ID ERO | | | |
| | | IPv4 Prefix Bypass | | 3 | >=0 |
| | | ERO | | | |
| | | IPv6 Prefix Bypass | | 4 | >=0 |
| | | ERO | | | |
| | | Unnumbered Interface | | 10 | >=0 |
| | | ID Bypass ERO | | | |
| | | All Router Block | | 6 | >=0 |
| | | All Router ID IPv4 | | 7 | >=0 |
| | | Map | | | |
| | | All Router ID IPv6 | | 8 | >=0 |
| | | Map | | | |
+-----+--------+----------------------+------+---------+------------+
Table 1: IANA allocations
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The MPLS Label TLV requires a new sub-registry. Type value 149 has
been assigned, with a starting sub-TLV value of 1, range from 1-127,
and managed by Expert Review.
8. Security Considerations
This document does not introduce any change in terms of IS-IS
security. It simply proposes to flood MPLS label information via the
IGP. All existing procedures to ensure message integrity do apply
here.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, May 2001.
[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.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling",
RFC 4761, January 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
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[RFC5151] Farrel, A., Ayyangar, A., and JP. Vasseur, "Inter-Domain
MPLS and GMPLS Traffic Engineering -- Resource Reservation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 5151, February 2008.
[RFC5302] Li, T., Smit, H., and T. Przygienda, "Domain-Wide Prefix
Distribution with Two-Level IS-IS", RFC 5302,
October 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5311] McPherson, D., Ginsberg, L., Previdi, S., and M. Shand,
"Simplified Extension of Link State PDU (LSP) Space for
IS-IS", RFC 5311, February 2009.
[RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Engineering in IS-IS", RFC 6119, February 2011.
9.2. Informative References
[I-D.gredler-rtgwg-igp-label-advertisement]
Gredler, H., Amante, S., Scholl, T., and L. Jalil,
"Advertising MPLS labels in IGPs",
draft-gredler-rtgwg-igp-label-advertisement-05 (work in
progress), May 2013.
[I-D.ietf-rtgwg-mrt-frr-architecture]
Atlas, A., Kebler, R., Envedi, G., Csaszar, A., Tantsura,
J., Konstantynowicz, M., White, R., and M. Shand, "An
Architecture for IP/LDP Fast-Reroute Using Maximally
Redundant Trees", draft-ietf-rtgwg-mrt-frr-architecture-02
(work in progress), February 2013.
[I-D.previdi-filsfils-isis-segment-routing]
Previdi, S., Filsfils, C., Bashandy, A., Horneffer, M.,
Decraene, B., Litkowski, S., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., and J. Tantsura, "Segment
Routing with IS-IS Routing Protocol",
draft-previdi-filsfils-isis-segment-routing-02 (work in
progress), March 2013.
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Authors' Addresses
Hannes Gredler (editor)
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
Shane Amante
Level 3 Communications, Inc.
1025 Eldorado Blvd
Broomfield, CO 80021
US
Email: shane@level3.net
Tom Scholl
Amazon
Seattle, WN
US
Email: tscholl@amazon.com
Luay Jalil
Verizon
1201 E Arapaho Rd.
Richardson, TX 75081
US
Email: luay.jalil@verizon.com
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