IGP Color-Aware Routing
draft-lin-lsr-igp-car-01
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Changwang Lin , Mengxiao Chen , Liyan Gong | ||
| Last updated | 2024-04-21 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-lin-lsr-igp-car-01
Network Working Group C. Lin
Internet Draft M. Chen
Intended status: Standards Track New H3C Technologies
Expires: October 19, 2024 L. Gong
China Mobile
April 22, 2024
IGP Color-Aware Routing
draft-lin-lsr-igp-car-01
Abstract
This document describes an IGP based routing solution to establish
end-to-end intent-aware paths across a multi-domain service provider
transport network.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 19, 2024.
Copyright Notice
Copyright (c) 2024 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
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction...................................................2
1.1. Requirements Language.....................................3
2. IGP CAR Solution...............................................3
2.1. SR Policy based IGP CAR...................................4
2.2. Flex-Algo based IGP CAR...................................5
2.3. Hybrid IGP CAR............................................7
3. Advertisement of IGP CAR Route.................................9
3.1. IS-IS CAR Sub-TLV.........................................9
3.1.1. IS-IS CAR MPLS-SR Encapsulation Sub-sub-TLV.........10
3.1.2. IS-IS CAR SRv6 Encapsulation Sub-sub-TLV............11
3.2. OSPF CAR Sub-TLV.........................................11
3.2.1. OSPF CAR MPLS-SR Encapsulation Sub-sub-TLV..........12
3.2.2. OSPF CAR SRv6 Encapsulation Sub-sub-TLV.............13
4. Resolving of IGP CAR Route....................................13
4.1. Resolving Over SR Policy.................................15
4.2. Resolving Over Flex-Algo.................................15
5. Security Considerations.......................................16
6. IANA Considerations...........................................16
7. References....................................................16
7.1. Normative References.....................................16
7.2. Informational References.................................16
Authors' Addresses...............................................18
1. Introduction
[I-D.hr-spring-intentaware-routing-using-color] describes the scope,
set of use-cases and requirements for a distributed routing based
solution to establish end-to-end intent-aware paths spanning multi-
domain packet networks. [I-D.ietf-idr-bgp-car] proposes a BGP based
solution called "BGP Color-Aware Routing" (BGP CAR). [I-D.ietf-idr-
bgp-ct] also proposes a BGP based solution called "BGP Classful
Transport" (BGP CT).
Network operators often organize networks into multiple smaller
network domains, and each network domain typically runs an IGP. In
some scenarios, only the PE nodes run the BGP protocol, while the
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other nodes (including the ASBR nodes) run only the IGP protocol, as
shown in Figure 1.
BGP
......................................
: :
: +----------+----------+----------+ :
: | | | | :
: | ASBR121 ASBR231 | :
: | | | | :
PE1+ D1 | D2 | D3 +PE2
| | | |
| ABSR122 ASBR232 |
| | | |
+----------+----------+----------+
|---IGP1---|---IGP2---|---IGP3---|
Figure 1: Multi IGP Domain Network Example
The BGP based solutions proposed by [I-D.ietf-idr-bgp-car] and [I-D.
ietf-idr-bgp-ct] require the ASBR nodes to run BGP and signal BGP
routes for CAR path. However, some network operators may not want to
change existing routing protocol deployments.
This document describes an IGP based routing solution to establish
end-to-end intent-aware paths, without requirement for the ASBR
nodes to run BGP.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. IGP CAR Solution
The following sub-sections illustrate example scenarios of Colored
Service Route Steering over E2E IGP CAR resolving over different
intra-domain mechanisms.
The examples use MPLS-SR for the transport data plane. The main
difference on SRv6 data plane is the replacement of CAR labels with
CAR SIDs.
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The OSPF and IS-IS extensions for advertising CAR route will be
described in Section 3. The resolving of CAR route will be described
in Section 4.
2.1. SR Policy based IGP CAR
Figure 2 illustrates an example scenario of Colored Service Route
Steering over E2E IGP CAR based on SR Policy.
RD:V/v via E2
+--+ vpn label:30030
.............................|RR|<............................
: +--+ Color C1 :
: :
+:-------------------+--------------------+-------------------:+
|: | | :|
|: Redist: Pfx=E2 | Redist: Pfx=E2 | :|
|: (C1,LI=8002)<~~|~~~ (C1,LI=8002)<~~|~~~ :|
|: +---+ +---+ SR Policy(C1,E2):|
|: |-------------->|121|--------------->|231|---------------| :|
|: | SR Policy +---+ SR Policy +---+ | :|
|: | (C1,121) | (C1,231) | CAR route: v :|
|--+ | | Pfx=E2 +--|
|E1| | | C=C1 |E2|
|--+ Redist: Pfx=E2 | Redist: Pfx=E2 | LI=8002+--|
| | (C1,LI=8002)<~~|~~~ (C1,LI=8002)<~~|~~~ ^ |
| | +---+ +---+ | |
| |-------------->|122|--------------->|232|---------------| |
| SR Policy +---+ SR Policy +---+ SR Policy |
| (C1,122) | (C1,232) | (C1,E2) |
| | | |
| IGP 1 | IGP 2 | IGP 3 |
+--------------------+--------------------+--------------------+
iPE iASBR eASBR ePE
+------+ +------+ +------+
| S1 | | S2 | | S3 |
+------+ +------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 2: SR Policy based IGP CAR Path
With reference to the topology above:
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o SR Policy provides intent in each domain.
o Egress PE E2 advertises a VPN route RD:V/v colored with (color
extended community) C1 to steer traffic to SR Policy. VPN route
propagates via RR(s) to ingress PE E1.
o IGP CAR route of prefix E2 with color C1 and label 168002 (index
is 2 and SRGB is 168000) is advertised by Egress PE E2, and
redistributed by ASBRs.
o On each ASBR and the Ingress PE E1, CAR label 168002 is resolved
over SR Policy of the domain.
o Ingress PE E1 steers colored VPN route RD:V/v into SR Policy
according to color.
Packet forwarding:
@E1: IPv4 VRF V/v => PUSH <S1, 168002, 30030>
@E1: MPLS Table: S1 => forward via SR Policy to 121
@121: MPLS Table: 168002 => PUSH S2
@121: MPLS Table: S2 => forward via SR Policy to 231
@231: MPLS Table: 168002 => PUSH S1
@231: MPLS Table: S3 => forward via SR Policy to E2
@E2: MPLS Table: 168002 => POP => MPLS Table: 30030 => POP and
lookup the IP DA in the VRF
2.2. Flex-Algo based IGP CAR
Figure 3 illustrates an example scenario of Colored Service Route
Steering over E2E IGP CAR based on Flex-Algo (FA).
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RD:V/v via E2
+--+ vpn label:30030
.............................|RR|<............................
: +--+ Color C1 :
: :
+:-------------------+--------------------+-------------------:+
|: | | :|
|: Redist: Pfx=E2 | Redist: Pfx=E2 | :|
|: (C1,LI=8002)<~~|~~~ (C1,LI=8002)<~~|~~~ :|
|: +---+ +---+ :|
|: Pfx-sid=8121|121| Pfx-sid=8231|231| :|
|: Algo=128 +---+ Algo=128 +---+ CAR route: :|
|--+ | | Pfx=E2 +--|
|E1| | | C=C1 |E2|
|--+ Redist: Pfx=E2 | Redist: Pfx=E2 | LI=8002+--|
| (C1,LI=8002)<~~|~~~ (C1,LI=8002)<~~|~~~ |
| +---+ +---+ Pfx-sid=8021 |
| Pfx-sid=8122|122| Pfx-sid=8232|232| Algo=128 |
| Algo=128 +---+ Algo=128 +---+ |
| | | |
| IGP 1 | IGP 2 | IGP 3 |
| FA 128(Mapping C1) | FA 128(Mapping C1) | FA 128(Mapping C1) |
+--------------------+--------------------+--------------------+
iPE iASBR eASBR ePE
+------+ +------+ +------+
|168121| |168231| |168021|
+------+ +------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 3: FA based IGP CAR Path
With reference to the topology above:
o IGP FA 128 is running in each domain, and mapped to Color C1.
o Egress PE E2 advertises a VPN route RD:V/v colored with (color
extended community) C1 to steer traffic to IGP FA 128. VPN route
propagates via RR(s) to ingress PE E1.
o IGP CAR route of prefix E2 with color C1 and label 168002 (index
is 8002 and SRGB is 160000) is advertised by Egress PE E2, and
redistributed by ASBRs.
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o On each ASBR and the Ingress PE E1, label 168002 is resolved over
IGP FA 128 of the domain.
o Ingress PE E1 steers colored VPN route RD:V/v into IGP FA 128
according to the mapping relationship between FA and Color.
Packet forwarding:
@E1: IPv4 VRF V/v => PUSH <168121, 168002, 30030>
@E1: MPLS Table: 168121 => forward via FA path to 121
@121: MPLS Label: 168002 => PUSH 168231
@121: MPLS Label: 168231 => forward via FA path to 231
@231: MPLS Label: 168002 => PUSH 168021
@231: MPLS Label: 168021 => forward via FA path to E2
@E2: MPLS Label: 168002 => POP => 30030 => POP and lookup the IP DA
in the VRF
2.3. Hybrid IGP CAR
Figure 4 illustrates an example where the same intent is provided by
SR Policy in some domains but by Flex-Algo in some other domains.
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RD:V/v via E2
+--+ vpn label:30030
.............................|RR|<............................
: +--+ Color C1 :
: :
+:-------------------+--------------------+-------------------:+
|: | | :|
|: Redist: Pfx=E2 | Redist: Pfx=E2 | :|
|: (C1,LI=8002)<~~|~~~ (C1,LI=8002)<~~|~~~ :|
|: +---+ +---+ SR Policy(C1,E2):|
|: |-------------->|121| Pfx-sid=8231|231|---------------| :|
|: | SR Policy +---+ Algo=128 +---+ | :|
|: | (C1,121) | | CAR route: v :|
|--+ | | Pfx=E2 +--|
|E1| | | C=C1 |E2|
|--+ Redist: Pfx=E2 | Redist: Pfx=E2 | LI=8002+--|
| | (C1,LI=8002)<~~|~~~ (C1,LI=8002)<~~|~~~ ^ |
| | +---+ +---+ | |
| |-------------->|122| Pfx-sid=8232|232|---------------| |
| SR Policy +---+ Algo=128 +---+ SR Policy |
| (C1,122) | | (C1,E2) |
| | | |
| IGP 1 | IGP 2 | IGP 3 |
| Algo 0 | FA 128(Mapping C1) | Algo 0 |
+--------------------+--------------------+--------------------+
iPE iASBR eASBR ePE
+------+ +------+ +------+
| S1 | |168231| | S3 |
+------+ +------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 4: Hybrid IGP CAR Path
With reference to the topology above:
o SR Policy provides intent in domain 1 and domain 3. IGP FA 128 is
running only in domain 2, and mapped to Color C1.
o IGP CAR route of prefix E2 with color C1 and label 168002 (index
is 2 and SRGB is 168000) is advertised by Egress PE E2, and
redistributed by ASBRs.
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o On ASBR 231 and the Ingress PE E1, label 168002 is resolved over
SR Policy. On ASBR 121, label 168002 is resolved over IGP FA 128
Packet forwarding:
@E1: IPv4 VRF V/v => PUSH <S1, 168002, 30030>
@E1: MPLS Table: S1 => forward via SR Policy to 121
@121: MPLS Label: 168002 => PUSH 168231
@121: MPLS Label: 168231 => forward via FA path to 231
@231: MPLS Table: 168002 => PUSH S1
@231: MPLS Table: S3 => forward via SR Policy to E2
@E2: MPLS Label: 168002 => POP => 30030 => POP and lookup the IP DA
in the VRF
3. Advertisement of IGP CAR Route
The advertisement of IGP CAR route is as following:
Prefix TLV: E
CAR Sub-TLV: C
CAR Encapsulation Sub-sub-TLV: T
The new-defined CAR sub-TLV is attached to a prefix E, indicating a
color-aware path of color C and encapsulation T towards that prefix.
On the MPLS-SR data plane, T is a label or index. On the SRv6 data
plane, T is an SRv6 SID.
If there are multiple color-aware path for different intents towards
the same E. Multiple CAR sub-TLVs with different colors will be
advertised.
Prefix TLV: E
CAR Sub-TLV: C1 + T1
CAR Sub-TLV: C2 + T2
CAR Sub-TLV: C3 + T3
...
3.1. IS-IS CAR Sub-TLV
The IS-IS CAR Sub-TLV is defined in this document to advertise CAR
information for prefixes in IS-IS. The IS-IS CAR Sub-TLV is
applicable to TLVs 27, 135, 235, 236, and 237.
The Sub-TLV 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 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-sub-TLV-len| Sub-sub-TLVs (variable)... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TBD.
o Length: 1 octet. The length value is variable.
o Flags: 2 octets. No flags are defined in this document. Undefined
flags MUST be set to 0 by the sender, and any unknown flags MUST
be ignored by the receiver.
o Color: 4 octets. Contains color value associated with the prefix.
o Sub-sub-TLV-length: 1 octet. Number of octets used by sub-sub-
TLVs.
o Sub-sub-TLVs: Carrying the encapsulation information. IS-IS CAR
MPLS-SR Encapsulation sub-sub-TLV and IS-IS CAR SRv6
Encapsulation sub-sub-TLV are defined in Section 3.1.1 and 3.1.2.
Other encapsulations may be defined in the future.
3.1.1. IS-IS CAR MPLS-SR Encapsulation Sub-sub-TLV
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: 1.
o Length: 3 or 4.
o SID/Label: If the length is set to 3, then the 20 rightmost bits
represent an MPLS label. If the length is set to 4, then the
value is a 32-bit index.
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3.1.2. IS-IS CAR SRv6 Encapsulation Sub-sub-TLV
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 (128 bits) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (cont . . .) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (cont . . .) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (cont . . .) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: 2.
o Length: 16.
o SID: 16 octets. This field encodes the SRv6 SID.
3.2. OSPF CAR Sub-TLV
The OSPF CAR Sub-TLV is defined in this document to advertise CAR
information for prefixes in OSPFv2 and OSPFv3. The OSPF CAR Sub-TLV
is applicable to OSPFv2 Extended Prefix TLV, OSPFv3 Inter-Area-
Prefix TLV, OSPFv3 Intra-Area-Prefix TLV, and OSPFv3 External-Prefix
TLV.
The Sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-sub-TLVs (variable)... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TBD.
o Length: 1 octet. The length value is variable.
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o Flags: 2 octets. No flags are defined in this document.
Undefined flags MUST be set to 0 by the sender, and any unknown
flags MUST be ignored by the receiver.
o Color: 4 octets. Contains color value associated with the prefix.
o Sub-sub-TLVs: Carrying the encapsulation information. OSPF CAR
MPLS-SR Encapsulation sub-sub-TLV and OSPF CAR SRv6 Encapsulation
sub-sub-TLV are defined in Section 3.2.1 and 3.2.2. Other
encapsulations may be defined in the future.
3.2.1. OSPF CAR MPLS-SR Encapsulation Sub-sub-TLV
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: 1.
o Length: 3 or 4.
o SID/Label: If the length is set to 3, then the 20 rightmost bits
represent an MPLS label. If the length is set to 4, then the
value is a 32-bit index.
OSPF CAR MPLS-SR Encapsulation Sub-sub-TLV is applicable to the OSPF
CAR Sub-TLV carried in OSPFv2 Extended Prefix TLV.
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3.2.2. OSPF CAR SRv6 Encapsulation Sub-sub-TLV
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 (128 bits) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (cont . . .) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (cont . . .) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (cont . . .) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: 2.
o Length: 16.
o SID: 16 octets. This field encodes the SRv6 SID.
OSPF CAR SRv6 Encapsulation Sub-sub-TLV is applicable to the OSPF
CAR Sub-TLV carried in OSPFv3 Inter-Area-Prefix TLV, OSPFv3 Intra-
Area-Prefix TLV, and OSPFv3 External-Prefix TLV.
4. Resolving of IGP CAR Route
When the ASBR or Ingress PE receives the IGP CAR route, it will be
resolved over the CAR paths, and then installed to CAR Route
Database (CARDB). CARDB is a logical collection of resolved CAR
routes. The ASBR can redistribute the CAR routes in CARDB to other
IGP instances. The Ingress PE can use the CARDB for next-hop
resolution of BGP colored service route.
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IGP Instance A
+-----------------------------+
|IGP CAR Route |
| | |
| | Resolving over CAR path|
| | 1. SR Policy |
| | 2. Flex-Algo |
| | ... |
+----+------------------------+
|
|Installation +--------------+
v +->|IGP Instance B|
+----+----+ | +--------------+
| CAR | Redistribution | +--------------+
| Route |----------------+->|IGP Instance C|
| Database| | +--------------+
+----+----+ | +--------------+
| +->| ... |
|Next-hop Resolution +--------------+
v
+----+----+
| BGP |
+---------+
Figure 5: CAR Route Database
Take the following IGP CAR Route on MPLS-SR data plane as an
example:
Advertiser: N
Prefix TLV: E
CAR Sub-TLV: C1 + L1
CAR Sub-TLV: C2 + L2
CAR Sub-TLV: C3 + L3
CAR Sub-TLV: C4 + L4
Assume that:
C1 is mapped to FA 128, and N's Prefix-SID in algorithm 128 is L128.
C2 is mapped to FA 129, and N's Prefix-SID in algorithm 129 is L129.
C3 path is provided by SR Policy 1 (C3, N) with segment-list S1.
C4 path is provided by SR Policy 2 (C4, N) with segment-list S2.
When the ASBR or Ingress PE resolved it over the CAR paths, the
example of MPLS forwarding entries is as following:
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+=======+==========+===========+=====================+
| Index | In-Label | Out-Label | Next-Hop & Out-Intf |
+=======+==========+===========+=====================+
| 1 | L1 | <L128,L1> | FA 128 Path |
+-------+----------+-----------+---------------------+
| 2 | L2 | <L129,L2> | FA 129 Path |
+-------+----------+-----------+---------------------+
| 3 | L3 | <S1,L3> | SR Policy 1 Path |
+-------+----------+-----------+---------------------+
| 4 | L4 | <S2,L4> | SR Policy 2 Path |
+-------+----------+-----------+---------------------+
The example of CAR route entries installed in the CARDB is as
following:
+========+=======+=========+=================+
| Key | Encap | Proto | Forwarding Path |
+========+=======+=========+=================+
| E + C1 | L1 | IS-IS 1 | MPLS Index 1 |
+--------+-------+---------------------------+
| E + C2 | L2 | IS-IS 1 | MPLS Index 2 |
+--------+-------+---------------------------+
| E + C3 | L3 | IS-IS 1 | MPLS Index 3 |
+--------+-------+---------------------------+
| E + C4 | L4 | IS-IS 1 | MPLS Index 4 |
+--------+-------+---------------------------+
The resolving of IGP CAR route SHOULD only be enabled on the ASBR
and Ingress PE. The P nodes do not need to resolve IGP CAR routes,
and only do SPF computation for the prefix of Egress PE, providing
best-effort forwarding for traditional services.
4.1. Resolving Over SR Policy
Resolving of IGP CAR Route over SR Policy can use the enhanced IGP
shortcut mechanism in [I-D.cheng-lsr-igp-shortcut-enhancement].
Briefly, the main point is to choose the SR Policy with the same
color as the next-hop.
4.2. Resolving Over Flex-Algo
When resolving of IGP CAR Route over Flex-Algo, the node will
determine the FA to which the color is mapped, and check if the
advertiser node is reachable in the topology of that FA. If yes, use
the FA path as next-hop, and add the Prefix-SID or SRv6 End SID
associated with that FA into encapsulation.
The mapping relationship of FA and color should be pre-configured.
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5. Security Considerations
TBD.
6. IANA Considerations
TBD.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017
[I-D.cheng-lsr-igp-shortcut-enhancement] Cheng, W., Gong, L., Lin,
C., and M. Chen, "IGP Shortcut Enhancement", Work in
Progress, Internet-Draft, draft-cheng-lsr-igp-shortcut-
enhancement-03, 27 Feburary 2024,
<https://datatracker.ietf.org/doc/html/draft-cheng-lsr-
igp-shortcut-enhancement-03>.
7.2. Informational References
[I-D.hr-spring-intentaware-routing-using-color] Hegde, S., Rao, D.,
Sangli, S. R., Agrawal, S., Filsfils, C., Talaulikar, K.,
Patel, K., Uttaro, J., Decraene, B., Bogdanov, A., Jalil,
L., Alston, A., Xu, X., Gulko, A., Khaddam, M., Contreras,
L. M., Steinberg, D., Guichard, J., Henderickx, W., and
Co-authors, "Problem statement for Inter-domain Intent-
aware Routing using Color", Work in Progress, Internet-
Draft, draft-hr-spring-intentaware-routing-using-color-03,
23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-hr-spring-
intentaware-routing-using-color-03>.
[I-D.ietf-idr-bgp-car] Rao, D., Agrawal, S., and Co-authors, "BGP
Color-Aware Routing (CAR)", Work in Progress, Internet-
Draft, draft-ietf-idr-bgp-car-07, 3 April 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
car-07>.
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[I-D.ietf-idr-bgp-ct] Vairavakkalai, K. and N. Venkataraman, "BGP
Classful Transport Planes", Work in Progress, Internet-
Draft, draft-ietf-idr-bgp-ct-31, 10 April 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ct-31>.
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Authors' Addresses
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Mengxiao Chen
New H3C Technologies
China
Email: chen.mengxiao@h3c.com
Liyan Gong
China Mobile
China
Email: gongliyan@chinamobile.com
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