Internet DRAFT - draft-zzhang-bess-mvpn-evpn-segmented-forwarding
draft-zzhang-bess-mvpn-evpn-segmented-forwarding
BESS Z. Zhang
Internet-Draft Juniper Networks
Updates: 6513, 6514, 7524 (if approved) J. Xie
Intended status: Standards Track Huawei
Expires: June 23, 2019 December 20, 2018
MVPN/EVPN Segmentated Forwarding Options
draft-zzhang-bess-mvpn-evpn-segmented-forwarding-00
Abstract
[RFC6513] and [RFC6514] specify MVPN Inter-AS Segmentation
procedures. [RFC7524] specifies MVPN Inter-Area Segmentation
procedures. [I-D.ietf-bess-evpn-bum-procedure-updates] specifies
EVPN BUM Inter-Region Segmentation Procedures. Several other
documents also touch upon the segmentation topic. The forwarding at
the segmentation points has been assumed to be label switching,
subject to certain limitations. The purpose of this document is to
provide a review of segmentation points' available forwarding options
and limitations, and to clarify and expand some procedures.
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 [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 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 June 23, 2019.
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Copyright Notice
Copyright (c) 2018 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
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. MPLS Label Switching at Segmentation Points . . . . . . . 3
2.2. IP Processing at Segmentation Points . . . . . . . . . . 5
3. Specifications . . . . . . . . . . . . . . . . . . . . . . . 6
4. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Normative References . . . . . . . . . . . . . . . . . . 6
4.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Terminology
This document uses terminology from MVPN and EVPN. It is expected
that the audience is familiar with the concepts and procedures
defined in [RFC6513], [RFC6514], [RFC7524], [RFC7432], [I-D.ietf-
bess-evpn-bum-procedure-updates], and [I-D.ietf-bess-evpn-igmp-mld-
proxy]. Some terms are listed below for references.
o PMSI: P-Multicast Service Interface - a conceptual interface for a
PE to send customer multicast traffic to all or some PEs in the
same VPN. A PMSI A-D route is a BGP MVPN/EVPN auto-discovery
route that announces the PMSI and optionally the tunnel that
instantiates the PMSI.
o I-PMSI: Inclusive PMSI - to all PEs in the same VPN.
o S-PMSI: Selective PMSI - to some of the PEs in the same VPN.
o Leaf A-D routes: For explicit leaf tracking purpose. Triggered by
S-PMSI A-D routes and targeted at triggering route's originator.
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o IMET A-D route: Inclusive Multicast Ethernet Tag A-D route. The
EVPN equivalent of MVPN Intra-AS I-PMSI A-D route.
o SMET A-D route: Selective Multicast Ethernet Tag A-D route. The
EVPN equivalent of MVPN Leaf A-D route but unsolicited and
untargeted.
2. Introduction
[RFC6513] and [RFC6514] specify MVPN Inter-AS Segmentation
procedures. [RFC7524] specifies MVPN Inter-Area Segmentation
procedures. [I-D.ietf-bess-evpn-bum-procedure-updates] specifies
EVPN BUM Inter-Region Segmentation Procedures. Several other
documents also touch upon the segmentation topic.
2.1. MPLS Label Switching at Segmentation Points
It has been assumed that the forwarding across a segmentation point
is label based. The upstream segment of a PMSI tunnel is stitched to
the downstream segment via label switching and no IP processing is
done. This is true even if the segmentation point also has a VRF
with PE-CE interfaces, where IP processing is done to decide if a
packet should be forwarded out of a PE-CE interface but label
switching is used for forwarding traffic to receivers connected by
downstream segments.
This label switching is based on the assumption/requirement that each
PMSI tunnel has its own unique label (in the simpliest case - this
can be relaxed as specified in [RFC7988] in case of Ingress
Relication). The following is a breakdown of the various situations:
o If an aggregated RSVP-TE or mLDP P2MP tunnel, or BIER is used for
the upstream (or downstream) segment, the x-PMSI A-D route
received (or re-advertised, in case of downstream segment) by the
segmentation point carries a per-PMSI label in the PMSI Tunnel
Attribute (PTA). The BIER case is specified in
[I-D.ietf-bier-mvpn] and [I-D.ietf-bier-evpn].
o If a unique RSVP-TE or mLDP P2MP tunnel is used for for each
upstream segment, the segmentation point advertises a unique label
for each tunnel to the upstream node on the tunnel. Similarly, in
the downstream segment case, the segmenation point must receive a
unique tunnel label.
o If Ingress Replication is used for the upstream segment, the
segmentatation point may either simply advertise a different label
in each Leaf A-D route that it advertises, or use a more elaborate
procedure to decide how labels could be advertised while still
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allow correct label switching procedure, as specified in
Section 7.2 of [RFC7988].
Notice that in the case of P2MP tunnel, x-PMSI A-D routes are
required to advertise the tunnel identification and in case of tunnel
aggregation (BIER or aggregated P2MP tunnel) the x-PMSI A-D routes
are required to advertise the per-PMSI label. However, [I-D.ietf-
bess-mvpn-expl-track] introduces a "Leaf Information Required per
Flow" bit (LIR-pF) in the flags field of the PTA of wildcard S-PMSI
A-D routes, so that an ingress PE does not have to advertise
individual more specific S-PMSI A-D routes even if it wants to
explicitly track the leaves for more specific flows. This can be
used for RSVP-TE P2MP, Ingress Replication and BIER.
For EVPN, explicit tracking is based on unsolicited Selective
Multicast Ethernet Tag (SMET) A-D routes and LIR-pF is not used.
However, that is as if the LIR-pF flag was set in an implicit (C-*,
C-*) wildcard S-PMSI A-D route.
Both [I-D.ietf-bier-mvpn] and [I-D.ietf-bier-evpn] specify that the
LIR-pF flag MUST not be used with segmentation. That's because with
LIR-pF while an ingress PE can send a flow to only leaves tracked for
the flow, it does not advertise the label bound to the corresponding
PMSI for the flow (as the LIR-pF removes the need to advertise the
more specific S-PMSI routes).
The same restriction also applies if aggregated RSVP-TE P2MP tunnels
are used (the same tunnel could be used for multiple more specific
S-PMSIs but a per-PMSI label would be associated with each S-PMSI).
The LIR-pF flag removes the need for those more specific S-PMSI A-D
routes so no S-PMSI specific labels could be advertised for the
segmentation points to do label switching with.
The restriction does not apply to Ingress Replication because the
per-PMSI label is advertised in the Leaf A-D routes.
The restriction with BIER and aggregated RSVP-TE P2MP tunnel can be
lifted if the LIR-pF triggered more specific MVPN Leaf A-D routes or
the unsolicited EVPN SMET routes can trigger corresponding S-PMSI A-D
routes, so that the per-PMSI labels can be advertised. The concept
of triggering S-PMSI A-D routes by Leaf/SMET A-D routes is already
present in [RFC7524] and
[I-D.zzhang-bess-mvpn-evpn-cmcast-enhancements].
It may be argued that triggering S-PMSI A-D route from Leaf/SMET A-D
routes for mroe specific flows has the following concerns (which
leads to the consideration for forwarding option described in
Section 2.2):
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o Flooding of those extra more specific S-PMSI A-D routes
o Delay in setting up the forwarding state (as the segmentation
points now have to wait for the corresponding S-PMSI A-D route
from its upstream).
The first concern can be discounted that the burden of those extra
S-PMSI A-D routes are mainly in the control plane. The forwarding
plane does need to maintain addtional per-PMSI labels but it's much
better than the alertnative described in the following section.
The second concern can be mitigated by having the ingress PE delay
switching traffic over to the more specific S-PSMI. That way,
traffic will continue to be forwarded on the less specific PMSI (and
label switched by segmentation points) for a short period before
being moved to the more specific S-PMSI.
2.2. IP Processing at Segmentation Points
If the above mentioned discount/mitigation are not enough to address
the two concerns, IP processing can be used at segmentation points.
This will allow the use of LIR-pF with segemntation without
triggering those more specific S-PMSI A-D routes
[I-D.xie-bier-mvpn-segmented] .
Basically, a segmentation point will create an IP multicast
forwarding table for each "context", which could be for an EVPN
Broadcast Domain (BD), a L3 VPN, an L3 VPN Extranet, or even
something of smaller scope. An incoming packet on an upstream
segment is decapsulated and a corresponding IP multicat forwarding
table is identified. An IP lookup is performed and forwarded into
downstream segments accordingly.
While this does not require the S-PMSI A-D routes triggered by Leaf/
SMET routes (and corresponding label forwarding state), additional IP
forwarding tables and lookup are needed, which requires additional
memory and cycles in the forwarding path, additional code to maintain
the RIB/FIB tables, and additional OPEX to monitor them.
Nonetheless, if IP processing on a segmentation point is desired for
the reason of LIR-pF bit, the following could be done.
o Wildcard S-PMSI A-D routes with the LIR-pF flag are assigned with
different labels from those in x-PMSI routes w/o the flag, and
they lead to IP lookup. The labels can either be upstream
assigned or assigned from a Domain-wide Common Block (DCB)
[I-D.ietf-bess-mvpn-evpn-aggregation-label].
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o Labels in x-PMSI routes w/o the LIR-pF flag, which are different
from those in routes with the flag, lead to label switching.
o A Leaf A-D route with LIR-pF flag triggers corresponding (C-S,
C-G) or (C-*, C-G) routes used for IP lookup, if there is no
corresponding S-PMSI A-D route with LIR-pF flag.
o Upstream PE/ABR uses the label advertised in the matching x-PMSI
routes to send traffic (so the packets will either be label
switched or ip forwarded by segmentation points).
On a PE, there are already VRFs or BDs configured so the IP RIBs/FIBs
are just in those VRFs/BDs. On a segmentation point, most likely
there are no VRFs/BDs. How IP RIBs/FIBs are managed is local
behavior and implementation dependent. While it is outside the scope
of this document, one method could be to maintain one IP RIB/FIB for
each label carried in a wildcard S-PMSI A-D route with the LIR-pF
flag. .
3. Specifications
Detail specification for the above summary will be added in upcoming
revisions.
4. References
4.1. Normative References
[I-D.ietf-bess-evpn-bum-procedure-updates]
Zhang, Z., Lin, W., Rabadan, J., Patel, K., and A.
Sajassi, "Updates on EVPN BUM Procedures", draft-ietf-
bess-evpn-bum-procedure-updates-05 (work in progress),
December 2018.
[I-D.ietf-bess-evpn-igmp-mld-proxy]
Sajassi, A., Thoria, S., Patel, K., Yeung, D., Drake, J.,
and W. Lin, "IGMP and MLD Proxy for EVPN", draft-ietf-
bess-evpn-igmp-mld-proxy-02 (work in progress), June 2018.
[I-D.ietf-bess-mvpn-expl-track]
Dolganow, A., Kotalwar, J., Rosen, E., and Z. Zhang,
"Explicit Tracking with Wild Card Routes in Multicast
VPN", draft-ietf-bess-mvpn-expl-track-13 (work in
progress), November 2018.
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[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>.
[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>.
[RFC7524] Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T.,
Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area
Point-to-Multipoint (P2MP) Segmented Label Switched Paths
(LSPs)", RFC 7524, DOI 10.17487/RFC7524, May 2015,
<https://www.rfc-editor.org/info/rfc7524>.
4.2. Informative References
[I-D.ietf-bess-mvpn-evpn-aggregation-label]
Zhang, Z., Rosen, E., Lin, W., Li, Z., and I. Wijnands,
"MVPN/EVPN Tunnel Aggregation with Common Labels", draft-
ietf-bess-mvpn-evpn-aggregation-label-02 (work in
progress), December 2018.
[I-D.ietf-bier-evpn]
Zhang, Z., Przygienda, T., Sajassi, A., and J. Rabadan,
"EVPN BUM Using BIER", draft-ietf-bier-evpn-01 (work in
progress), April 2018.
[I-D.ietf-bier-mvpn]
Rosen, E., Sivakumar, M., Aldrin, S., Dolganow, A., and T.
Przygienda, "Multicast VPN Using BIER", draft-ietf-bier-
mvpn-11 (work in progress), March 2018.
[I-D.xie-bier-mvpn-segmented]
Xie, J., Geng, L., Wang, L., McBride, M., and G. Yan,
"Segmented MVPN Using IP Lookup for BIER", draft-xie-bier-
mvpn-segmented-06 (work in progress), October 2018.
[I-D.zzhang-bess-mvpn-evpn-cmcast-enhancements]
Zhang, Z., Kebler, R., Lin, W., and E. Rosen, "MVPN/EVPN
C-Multicast Routes Enhancements", draft-zzhang-bess-mvpn-
evpn-cmcast-enhancements-00 (work in progress), July 2016.
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[RFC7988] Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress
Replication Tunnels in Multicast VPN", RFC 7988,
DOI 10.17487/RFC7988, October 2016,
<https://www.rfc-editor.org/info/rfc7988>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
Jingrong Xie
Huawei
EMail: xiejingrong@huawei.com
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