routing Z. Zhang
Internet-Draft Juniper Networks
Intended status: Standards Track October 25, 2021
Expires: April 28, 2022
MVPN Inter/Intra-region Tunnel Segmentation
draft-zzhang-bess-mvpn-regional-segmentation-01
Abstract
RFC7524 specifies procedures for Inter-Area Point-to-Multipoint
Segmented Label Switched Paths (aka MVPN tunnel segmentation). This
document updates RFC7524 by extending the inter-area segmentation
concept to inter-region and intra-region segmentation where a region
is no longer tied to an IGP area.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Tunnel Segmentation . . . . . . . . . . . . . . . . . . . 2
1.2. Intra-region Segmentation . . . . . . . . . . . . . . . . 3
1.3. Bud Node Support . . . . . . . . . . . . . . . . . . . . 3
2. Specifications . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Inter-region Segmentation . . . . . . . . . . . . . . . . 3
2.2. Intra-region Segmentation . . . . . . . . . . . . . . . . 4
2.3. Bud Node Support . . . . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
1.1. Tunnel Segmentation
[RFC6514] specifies (among other things) inter-AS MVPN tunnel
segmentation procedures and [RFC7524] specifies inter-area MVPN
tunnel segmentation procedures. The procedures for inter-AS and
inter-area are similar in that the segmentation points - ASBRs or
ABRs - change the PMSI Tunnel Attribute (PTA) attached to I/S-PMSI
routes to specify the type and identification of tunnel to be used in
the next AS/area, when they re-advertise the PMSI routes into the
next AS/area.
This change of tunnel at the segmentation points and stitching of
upstream and downstream tunnel segments not only allows different
tunnel technology/instance to be used in different AS/area, but also
limits the replication of traffic to only PEs and segmentation points
in the local AS/area, instead of to all PEs.
The inter-area segmentation points are route reflectors and when they
re-advertise the x-PMSI routes to different downstream areas they may
use different BGP neighbor groups so that different tunnel type/
identification can be encoded in PTA for different downstream areas.
If the ABR is also responsible for reflecting the routes to PEs in
the same area, the ABR does not modify the PTA (because of that those
local PEs are also put into a different neighbor group).
As a result, a segmentation point will likely have different neighbor
groups (one group for each area) so that the PTA and Inter-Area P2MP
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Segmented Next-Hop Extended Community (referred to as Segmentation
EC) can be set accordingly when it re-advertise the x-PMSI routes.
The provisioning of a RR with these different neighbor groups for
segmentation purpose can actually be done on any router (as a
segmentation point) - not necessarily on an ABR. As a result, the
procedures in RFC7524, while specified for inter-area, can be
extended inter-regiona as well - the segmentation points can be any
border routers between arbitrarily defined "regions".
This concept is already described in Section 6 of
[I-D.ietf-bess-evpn-bum-procedure-updates], but specified formally in
this document for MVPN.
1.2. Intra-region Segmentation
Even with the inter-area segmentation extended to inter-region, when
a regional border router (RBR) reflects routes to PEs in the same
region, it does not modify the PTA or Segmentation EC. But if the
RBR also modifies the two attributes when reflecting routes to the
local PEs, tunnel segmentation is achieved even intra-region - both
the upstream and downstream tunnel segments are in the same region.
This Intra-region Segmentation is one way to achieve Assisted
Replication in MVPN: a PE sends traffic to assisting replicators who
will then relay traffic to other PEs (even in the same region).
1.3. Bud Node Support
A segmentation point may have both local receivers off a VRF and
downstream receivers off a remote PE for traffic arriving on an
upstream segment. This segmentation point is referred to a bud node,
just like that a node can be both a transit and leaf node for a P2MP
tree.
Depending on implementation, a bud node may need to receive two
copies of a packet, one for local delivery and one for remote
delivery. If so, the bud node may request the upstream PE or
segmentation point to send two copies.
2. Specifications
2.1. Inter-region Segmentation
The procedures in RFC7524 are extended to beyond IGP area-based. A
provider network can be arranged into "regions" connected by
"Regional Border Routers" (RBRs). On a segmentation point a region
MAY be defined as a BGP neighbor group - all peers in the group are
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subject to the same export policy, which can be used to control the
modification of attributes for the purpose of segmentation.
RFC7524 procedures apply as is, though "area" is replaced with
"region" and "Area Border Router" (ABR) is replaced with "Regional
Border Router" (RBR).
The concept of Per-region Aggregation, as explained in Section 6.1 of
[I-D.ietf-bess-evpn-bum-procedure-updates], is also applicable to
MVPN. A future revision of this document will specify details of
Per-region Aggregation for MVPN.
2.2. Intra-region Segmentation
The following procedures are applicable for intra-region
segmentation. One use of intra-region segmentation is for Assisted
Replication where PE-PE traffic goes through a relay point (assisting
replicator).
If it is known that the local PEs are only peered with the RBRs (as
RRs and segmentation points), the PEs and RBRs follow the procedures
in RFC7524. In addition, the local RBRs modify the PTA and
Segmentation EC even when they re-advertise x-PMSI routes to PEs in
the ingress region, thus achieving Intra-region Segmentation.
Otherwise (i.e., if a local PE may import BGP-MVPN routes directly
unless with the modified procedures specified below), the following
modified procedures apply:
o When an ingress PE advertises an x-PMSI route, it attaches an
Extended Community (EC) derived from the Route Target for the VPN
(RT-VPN) [I-D.zzhang-idr-rt-derived-community] but not the RT-VPN
itself. Call this EC as EC-VPN. The route also carry a
Segmentation EC as specified in RFC7524.
o When the local RBRs (as RRs and segmentation points) receive this
route, it replaces the EC-VPN with the corresponding RT-VPN (the
EC-VPN and RT-VPN can be derived from each other), and then re-
advertise the route to its peers, with the Segmentation EC and PTA
modified as specified in RFC7524. The modification applies even
when re-advertising to peers in the same ingress region.
This is to ensure that local egress PEs will only import the routes
re-advertised by the RBRs after the modification of PTA and
Segmentation EC.
Additionally, if there are intermediate RRs between the ingress PE
and local RBRs, and Route Target Constrain [RFC4684] is in use, the
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ingress PE MUST also attach a Route Target (referred to as RT-RBR)
and the local RBRs MUST be provisioned to import routes with RT-RBR
(otherwise the intermediate RRs will not re-advertise the routes
towards the RBRs because the routes carry only EC-VPN but not RT-
VPN). The local RBRs MUST remove the RT-RBR when they re-advertise
the routes.
2.3. Bud Node Support
This section applies only if the segmentation point can not both
route traffic arriving on the upstream segment to local receivers and
label switch the traffic to downstream segments due to implementation
limitation.
If a segmentation point is a bud node for a segmented x-PMSI tunnel
with the above mentioned limitation, it SHOULD request an additional
copy to be sent by the upstream RSVP neighbor if the upstream segment
is a RSVP-TE P2MP tunnel, or by the upstream PE/RBR when the upstream
segment is an IR or mLDP tunnel.
The RSVP-TE P2MP case is outside the scope of this document (though
there are known implementations). For the IR/mLDP case, it is done
by including a Tunnel Encapsulation Attribute (TEA) [RFC9012] in the
Leaf A-D route in response to the x-PMSI route for the upstream
segment. Note that the leaf A-D route is sent for this purpose even
if the Leaf Information Required (LIR) flag is not set in the x-PMSI
route (e.g. for mLDP tunnel).
The TEA includes one tunnel of a desired type (e.g. MPLS or Any
Encapsulation [I-D.ietf-bess-bgp-multicast-controller]) that is used
for the upstream PE/RBR to send the additional copy to this bud node.
The tunnel MUST include a Tunnel Egress Endpoint sub-TLV set to a
loal address on the bud node, and MUST include a Tree Label Stack
sub-TLV that includes a single label. The node MUST program a label
forwarding entry to pop the label and forward packet based on IP
lookup in a VRF identified by the label (while the tunnel label for
the upstream segment or the label in the PTA of the x-PMSI/Leaf route
for the upstream segment is used to stitch the upstream and
downstream segments together).
When the upstream PE/RBR decodes the TEA in the Leaf A-D route in
response to an x-PMSI A-D route that it (re-)advertises (even if it
did set the LIR flag in the x-PMSI A-D route), it SHOULD send an
extra copy via unicast tunneling with the label encoded in the Tree
Label Stack sub-TLV. If the extra copy is not sent the downstream
bud node segmentation point will not be able to send traffic to its
local receivers.
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3. Security Considerations
No additional security considerations are needed beyond what are
discussed in RFC7524.
4. IANA Considerations
This document requests the IANA to create a "PMSI Tunnel Attribute
Extension sub-TLV Type Registry". Allocation from the registry is
First Come First Serve, with an initial allocation for "Additional
Label".
5. Acknowledgements
The author thanks Sanoj Vivekanandan for his review and comments.
6. References
6.1. Normative References
[I-D.ietf-bess-bgp-multicast-controller]
Zhang, Z., Raszuk, R., Pacella, D., and A. Gulko,
"Controller Based BGP Multicast Signaling", draft-ietf-
bess-bgp-multicast-controller-07 (work in progress), July
2021.
[]
Zhang, Z., "Extended Communities Derived from Route
Targets", draft-zzhang-idr-rt-derived-community-01 (work
in progress), March 2021.
[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>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
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6.2. Informative 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-11 (work in progress),
October 2021.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
Author's Address
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
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