Internet DRAFT - draft-duan-bess-simplified-mvpn-for-bier-and-ir
draft-duan-bess-simplified-mvpn-for-bier-and-ir
Network Working Group F. Duan
Internet-Draft S. Chen
Intended status: Standards Track Huawei Technologies
Expires: 4 September 2024 3 March 2024
Simplified MVPN for BIER and IR
draft-duan-bess-simplified-mvpn-for-bier-and-ir-02
Abstract
Per RFC6513 and RFC6514, seven MCAST-VPN NLRIs and relevant
procedures are defined to build multicast forwarding tree over the
service provider backbone. RFC8556 introduces that MVPN can use BIER
as PMSI tunnel to perform optimal multicast forwarding. However, the
complicated NLRI exchange and the switching from I-PMSI to S-PMSI
tunnel is not necessary for BIER and IR tunnel. The architectural
advantages of BIER and IR cannot be fully utilized. Therefore, a new
simplified MVPN for BIER and IR is proposed to substitute current
NLRIs exchange and procedures. This document would like to discuss
the value of the MVPN simplification and provide suggestive solution.
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 4 September 2024.
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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/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Simplification of Type 1 and 3 NLRI . . . . . . . . . . . 4
3.2. Simplification of Type 4, 6 and 7 NLRIs . . . . . . . . . 5
4. Segmentation scenario . . . . . . . . . . . . . . . . . . . . 6
5. Back compatibility . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
In [RFC4364], IP Virtual Private Networks (VPNs) are proposed to
forward unicast traffic from one VPN site to another. Afterwards,
[RFC6037] firstly combined VPN with IP Multicast and multicast
forwarding tree can be built over the provider backbone. PIM was the
only protocol to establish PMSI tunnels. [RFC6513] and [RFC6514]
then improved the MVPN procedure. On the one hand, more flexible
tunnel type such as P2MP and IR are specified. On the other hand,
seven MCAST-VPN NLRIs are defined to advertise the information of
MVPN members, tunnels, source location and join/prune messages. MVPN
solutions usually started with instantiate inclusive PMSI to build
the multicast distribution trees over the provider network.
In order to optimize the bandwidth utilization of the provider
backbone network, S-PMSI A-D Route is designed so that selective
multicast can be performed when the traffic of (C-S,C-G) exceeds the
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preset threshold. Switching from I-PMSI to S-PMSI is an inevitable
action for selective multicast when the tunnel type is mLDP or RSVP-
TE. Because new underlay tunnel establishing procedures are
necessary for these two tunnels. The switching results in the
complicated NLRI exchanging procedures.
[RFC8556] introduces that MVPN can use BIER to conduct optimal
multicast forwarding. The complicated NLRI exchanging procedures are
still maintained while those are unnecessary for BIER and Ingress
Replication Tunnel. There are several problems in current MVPN
procedures:
a. Even though per-flow multicast state is not maintained in the P
routers, ingress root PE still follows the traditional process of
building multicast tunnel. Root PE also needs to check whether
the amount of multicast flow exceeds the preset threshold at any
time so that it can initiate the switching from I-PMSI to S-PMSI.
The exchange of control-plane and data-plane are still very
complicated.
b. There are two types of NLRIs involved in the process of
customer's routes advertisement. Besides, four types of NLRIs
are leveraged to collect tunnel informations. The exchange of
NLRIs between each router is complicated.
The architectural advantages of BIER and IR are that they can
intrinsically support explicit tracking at the ingress PE. When LDP
and RSVP-TE tunnels are deployed, new MPLS labels or Opaque value are
assigned along each branches of the multicast tunnels when the S-PMSI
tunnels are initialized, which means new forwarding table are
constructed along each relevant routers. When underlay tunnel is
BIER or IR, S-PMSI tunnel can directly use the same forwarding table
of I-PMSI tunnel on each router. The only way to differentiate these
two tunnels is explicit tracking. Inress PE use explicit tracking to
specify different leaves in the multicast packet. Each leaf PE of
BIER and IR is globally unique from the perspective of ingress PE.
Therefore, S-PMSI tunnel can be constructed directly at first and
switching from I-PMSI to S-PMSI tunnel will no longer needed.
On the other hand, segment routing is widely discussed and
implemented nowadays and it is regarded as a simplification of MPLS.
SR-MPLS, SR-BIER and SR-IR are simplification of existing tunnel
types in a sense. With SR, current MVPN architecture and NLRI
exchanges seem to be too heavy. Under these circumstances, a light-
weight architecture of MVPN needs to be considered. In that way, the
feature of explicit tracking can also be fully utilized.
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One possible method is proposed in this document to simplify the MVPN
procedure for BIER and IR. There would be no inclusive PMSI tunnel.
Two new multicast routes and procedures are proposed to substitute
the existing seven NLRIs.
2. Terminology
The terminology used in this document is the terminology defined
in[RFC6513], [RFC6514] and [RFC8556].
For convenience of description, the abbreviations used in this
document is listed below.
NLRI: Network Layer Reachability Information
UMH: Upstream Multicast Hop
PMSI: P-Multicast Service Interface
VPN: Virtual Private Network
MVPN: Multicast VPN
RD: Route Distinguisher
IR: Ingress Replication
3. Specification
3.1. Simplification of Type 1 and 3 NLRI
Type 1 and 3 NLRIs may be replaced by the eligible UMH route. The
eligible UMH route was initially introduced in [RFC6513]. It
contains Source AS Extended Community and VRF Route Import Extended
Community. In this document, MS-ID and BIER attributes are added
into the eligible UMH route so that type 1 and 3 NLRIs are no longer
needed. When the leaf PE receives the eligible UMH routes, it will
import the unicast route into its local instance. Simultaneously,
the MS-ID will be used to generate the correspondence between the MS-
id and local instance. When the leaf PE receives the join or prune
messages, it will find the multicast source or RP in the unicast
routing-table of corresponding instance. The underlay BIER attribute
of the unicast route will be used.
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+------------------------------------------------+
| MS-ID (4 or 16 octets) |
+------------------------------------------------+
| Sub-domain ID (2 octets ) |
+------------------------------------------------+
| BFR-ID (2 octets ) |
+------------------------------------------------+
Figure 1: New MVPN Eligible UMH Route
3.2. Simplification of Type 4, 6 and 7 NLRIs
When leaf PE receives igmp membership report or pim join messages, it
will check whether the sub-domain-id inside the BIER attribute of the
unicast route is same as its local sub-domain-id. If the two IDs are
same, leaf PE will advertise a BGP multicast route to root PE. The
BGP multicast route is proposed in this document to replace Type 4, 6
and 7 NLRI. It contains RD, originator IP, source address and group
address. Additionally, it includes one-octet field called 'Flag'.
Flag is used to distinguish (C-*,C-G) Join, (C-S,C-G) Join and
(C-S,C-G,rpt) Prune. The route also includes BIER sub-domain-id and
BFR-id of leaf PE. The conventional Join and Prune of c-multicast
route are substituted by the update and withdraw of this BGP
multicast route. Moreover, Source AS Extended Community and VRF
Route Import Extended Community are also carried by the BGP multicast
route.
+------------------------------------------------+
| RD (8 octets) |
+------------------------------------------------+
| Source Address (4 or 16 octets, 0 to 32 / 128)|
+------------------------------------------------+
| Group Address (4 or 16 octets, 0 to 32 / 128) |
+------------------------------------------------+
| Flag (1 octet) |
+------------------------------------------------+
| Originating Router's IP Addr (4 / 16 octets) |
+------------------------------------------------+
| Sub-domain ID (2 octets ) |
+------------------------------------------------+
| BFR-ID (2 octets ) |
+------------------------------------------------+
Figure 2: New BGP Multicast Route
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4. Segmentation scenario
Adaption about Inter-AS I-PMSI A-D route has not been mentioned yet.
We are working on solution for tunnel segmentation scenario and
relevant solutions will be updated in later version.
5. Back compatibility
Back compatibility is a significant issue and will be discussed in
the future.
6. Security Considerations
//TODO
7. IANA Considerations
//TODO
8. Acknowledgements
//TODO
9. References
9.1. 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>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
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[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>.
[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>.
9.2. Informative References
[RFC6037] Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco
Systems' Solution for Multicast in BGP/MPLS IP VPNs",
RFC 6037, DOI 10.17487/RFC6037, October 2010,
<https://www.rfc-editor.org/info/rfc6037>.
Authors' Addresses
Fanghong Duan
Huawei Technologies
Email: duanfanghong@huawei.com
Siyu Chen
Huawei Technologies
Email: chensiyu27@huawei.com
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