BIER Anycast MPLS Label
draft-chen-bier-anycast-label-01
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Siyu Chen , Fanghong Duan | ||
| Last updated | 2024-03-17 | ||
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| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
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draft-chen-bier-anycast-label-01
Network Working Group S. Chen
Internet-Draft F. Duan
Intended status: Standards Track Huawei Technologies
Expires: 17 September 2024 16 March 2024
BIER Anycast MPLS Label
draft-chen-bier-anycast-label-01
Abstract
This document provides a method to reduce packet loss when failures
occur at BIER transit or egress nodes or link.
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.
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 https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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 17 September 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 (https://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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Egress Protection . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Anycast and Bypass MPLS Label . . . . . . . . . . . . . . 4
3.2. Advertisement of MPLS Label . . . . . . . . . . . . . . . 4
3.3. Establishment of BIER Forwarding Table . . . . . . . . . 5
3.4. Fast Recovery . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
When failures occur at transit or egress BIER node, there is no fast
recovery or protecting mechanism currently. The recovery duration
depends on how fast the unicast algorithm can re-calculate the new
path. The new available path can only be generated in this way
called 'IGP re-convergence'. In this document, a fast failover
method is designed for BIER to generate an alternative path for flow
in advance by allocating and transmitting additional BIER MPLS label
for certain network topology.
As shown in the following figure, two BFRs are deployed in each site.
Each BFR can be backup device for the other BFR within the site. CE
is connected to only one of the BFERs.
Site1 Site2 Site3
.... ---- BFR-E(ID:4) ---- BFER-C(ID:3)
|\ /| \ / |
| \ / | \ / |
| \ / | \ / |
| \/ | \ / |
| / \ | / \ |
| / \ | / \ |
| / \ | / \ |
SRC -- BFIR-A(ID:1) -- BFR-B ------- BFER-D(ID:2) -- CE -- RECEIVER
Figure 1: BIER Network Topology
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In [RFC8279], BIER MPLS label was assigned locally to identify
different set of [Sub-domain, SI, BSL] and therefore can identify
different instances of BIER Forwarding Table. In this document, a
BFR node will be assigned two MPLS Labels called 'Anycast' and
'Bypass' MPLS Label. Anycast MPLS Label will be used to represent
the site, while bypass MPLS label will only be used within each site
to ensure the forwarding function. The BIER Forwarding Table will
also be modified to record two different out interfaces for two
target BFR-IDs.
2. Terminology
The terminology used in this document is the terminology defined
in[RFC8279], [RFC8296] and [RFC8556].
For convenience of description, the abbreviations used in this
document is listed below.
BIER: Bit Index Explicit Replication
BGP: Border Gateway Protocol
IGP: Interior gateway protocol
BFR: Bit-Forwarding Router
BFR-ID: Bit-Forwarding Router ID
BFR-Prefix: Bit-Forwarding Router Prefix
BFR-NBR: Bit-Forwarding Router Neighbor
BIRT: Bit index routing table
BIFT: Bit index forwarding table
F-BM: Forwarding Bit Mask
MPLS: Multiprotocol Label Switching
3. Egress Protection
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3.1. Anycast and Bypass MPLS Label
As shown in the following figure, one customer device CE is connected
to BFER-D. Each site deploys two BFRs to perform failure protection,
different BFR-IDs and BFR-prefixes are configured. In this way, when
CE sends join towards BFER-D, the source and BFIR can clearly know
where the receiver is. Specially, BFRs in one site are assigned with
same Anycast MPLS Label and different Bypass MPLS labels. The same
Anycast Label can be used to specify the site. The Bypass MPLS Label
works as the traditional MPLS label to ensure the normal behavior of
BIER forwarding function within the site. The relationship between
[SD, BSL, SI], Anycast Label, Bypass Label will be maintained and
utilized when parsing BIER packets. Anycast and Bypass MPLS Labels
are then advertised by BIER-Info Sub-TLV in BIER prefix. After each
BFR receives BIER prefix, BIER MPLS Label will be contained in BIER
Forwarding Table to instruct forwarding data packet.
Site1 Site2 Site3
.... ---- BFR-E(1000) --- BFER-C(0100)
|\ /| \ / |
| \ / | \ / |
| \ / | \ / |
| \/ | \/ |
| / \ | / \ |
| / \ | / \ |
| / \ | / \ |
SRC -- BFIR-A(0001) -- BFR-B ---- BFER-D(0010) --- CE
Figure 2: BIER Network Topology with BFR-ID
3.2. Advertisement of MPLS Label
[RFC8401] defines BIER Info Sub-TLV to advertise BIER parameters such
as BFR-ID, subdomain-id. The key field of the Sub-TLV is BIER
prefix. Within the Sub-TLV, sub-sub-TLV is contained and it carries
MAX-SI, BSL and MPLS Label. The sub-sub-TLV is modified in this
document so that both Anycast and Bypass MPLS Labels can be
advertised.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI | BSL | (Bypass) Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI | BSL | Anycast Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: New BIER Info Sub-sub-TLV
3.3. Establishment of BIER Forwarding Table
After receiving BIER Info Sub-TLV, BFR will parse Bypass MPLS Label
and Anycast MPLS Label. The relationship of [BFR-ID, Anycast Label,
Bypass Label] will be maintained by each BFR.
The procedure of establishing BIFT is illustrated from the
perspective of BFR-B and the Topology is accordingly simplified. As
shown in the simplified topology figure below, BFR-B will receive
BIER Info Sub-TLVs from BFER-C and BFER-D. The Anycast Label of two
BFERs are different with BFR-B's, but they are same with each other.
BFR-B will combine BFR-ID of BFER-C and BFER-D into one entry in the
Bit Index Forwarding Table. Both BFER-C and BFER-D may receive
packet.
Site1 Site2 Site3
BFR-E(1000) -- BFER-C(0100)
| / |
BFR-A(0001)--- BFR-B ---- BFER-D(0010) ------- CE
Figure 4: Simplified Topology from BFR-B's Perspective
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BFR-B BIFT
--------------------------------------
| F-BM | BFR-NBR | NBR-Label |
=====================================
| 0001 | A | AnycastLabel-1 |
-------------------------------------
| 0110 | D | AnycastLabel-3 |
-------------------------------------
| C | AnycastLabel-3 |
-------------------------------------
| 1000 | E | BypassLabel-21 |
-------------------------------------
Figure 5: BFR-B's BIFT
When BFR-B receives BIER data packet, it will locate the BIFT
according to the BIFT-ID encapsulted in BIER header. If the packet
needs to be forwarded to BFR-ID 2, it will modify the BIFT-ID field
as AnycastLabel-3 and then forward it. When BFER-D receives this
packet, it will send the packet to CE.
BFERs will also advertise their BIER Info Sub-TLV to each other.
When BFER-C receives BFER-D's Sub-sub-TLV, it finds BFER-D has same
anycast label and different bypass label with itself. BFER-C will
encode Bypass MPLS label into its BIFT as shown below.
BFR-C BIFT
--------------------------------------
| F-BM | BFR-NBR | NBR-Label |
=====================================
| 0010 | D | BypassLabel-32 |
-------------------------------------
| 1001 | E | AnycastLabel-2 |
-------------------------------------
| B | AnycastLabel-2 |
-------------------------------------
Figure 6: BFR-C's BIFT
3.4. Fast Recovery
When link between BFR-B and BFER-D goes down due to certain reason,
BFR-B will detect it and forward packet to BFER-C immediately
according to BIFT entry. AnycastLabel-3 will be encapsulated. When
BFER-C receives this packet, it will firstly use anycast label to
locate corresponding BIFT table. Then it will use BFR-ID 2 to look
for F-BM and find its neighbor is BFER-D. The Bypass label of BFER-D
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will be encapsulated into data packet header. Then BFER-D will
finally receive the packet and forward it to CE. No packet will be
dropped because the backup out interface has been generated when the
anycast and bypass MPLS Labels are advertised and utilized.
In this way, reliance on unicast routing re-convergence after failure
are minimized. It is also compatible with existed BIER protocol and
signals such as BIER Info sub-TLV. This method is also friendly to
hardware platform. BIER forwarding procedures actually are not
modified.
4. Security Considerations
//TODO
5. IANA Considerations
//TODO
6. Acknowledgements
//TODO
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
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[RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
Zhang, "Bit Index Explicit Replication (BIER) Support via
IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
<https://www.rfc-editor.org/info/rfc8401>.
[RFC8556] Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
and A. Dolganow, "Multicast VPN Using Bit Index Explicit
Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
2019, <https://www.rfc-editor.org/info/rfc8556>.
Authors' Addresses
Siyu Chen
Huawei Technologies
Email: chensiyu27@huawei.com
Fanghong Duan
Huawei Technologies
Email: duanfanghong@huawei.com
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