draft-ietf-bess-datacenter-gateway-06.txt   draft-ietf-bess-datacenter-gateway-07.txt 
BESS Working Group A. Farrel BESS Working Group A. Farrel
Internet-Draft Old Dog Consulting Internet-Draft Old Dog Consulting
Intended status: Standards Track J. Drake Intended status: Standards Track J. Drake
Expires: December 3, 2020 E. Rosen Expires: December 6, 2020 E. Rosen
Juniper Networks Juniper Networks
K. Patel K. Patel
Arrcus, Inc. Arrcus, Inc.
L. Jalil L. Jalil
Verizon Verizon
June 1, 2020 June 4, 2020
Gateway Auto-Discovery and Route Advertisement for Segment Routing Gateway Auto-Discovery and Route Advertisement for Segment Routing
Enabled Domain Interconnection Enabled Domain Interconnection
draft-ietf-bess-datacenter-gateway-06 draft-ietf-bess-datacenter-gateway-07
Abstract Abstract
Data centers are critical components of the infrastructure used by Data centers are critical components of the infrastructure used by
network operators to provide services to their customers. Data network operators to provide services to their customers. Data
centers are attached to the Internet or a backbone network by gateway centers are attached to the Internet or a backbone network by gateway
routers. One data center typically has more than one gateway for routers. One data center typically has more than one gateway for
commercial, load balancing, and resiliency reasons. commercial, load balancing, and resiliency reasons.
Segment Routing is a protocol mechanism that can be used within a Segment Routing is a protocol mechanism that can be used within a
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 3, 2020. This Internet-Draft will expire on December 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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load balance the flows it sends to a destination (egress) DC, it load balance the flows it sends to a destination (egress) DC, it
needs to know the complete set of entry nodes (i.e., GWs) for that needs to know the complete set of entry nodes (i.e., GWs) for that
egress DC from the backbone network connecting the two DCs. Note egress DC from the backbone network connecting the two DCs. Note
that it is assumed that the connected set of DCs and the backbone that it is assumed that the connected set of DCs and the backbone
network connecting them are part of the same SR BGP Link State (LS) network connecting them are part of the same SR BGP Link State (LS)
instance ([RFC7752] and [I-D.ietf-idr-bgpls-segment-routing-epe]) so instance ([RFC7752] and [I-D.ietf-idr-bgpls-segment-routing-epe]) so
that traffic engineering using SR may be used for these flows. that traffic engineering using SR may be used for these flows.
SR may also be operated in other domains, such as access networks. SR may also be operated in other domains, such as access networks.
Those domains also need to be connected across backbone networks Those domains also need to be connected across backbone networks
through gateways. through gateways. For illustrative purposes, consider the Ingress
and Egress SR Domains shown in Figure 1 as spearate ASes.
Suppose that there are two gateways, GW1 and GW2 as shown in Suppose that there are two gateways, GW1 and GW2 as shown in
Figure 1, for a given egress SR domain and that they each advertise a Figure 1, for a given egress SR domain and that they each advertise a
route to prefix X which is located within the egress SR domain with route to prefix X which is located within the egress SR domain with
each setting itself as next hop. One might think that the GWs for X each setting itself as next hop. One might think that the GWs for X
could be inferred from the routes' next hop fields, but typically it could be inferred from the routes' next hop fields, but typically it
is not the case that both routes get distributed across the backbone: is not the case that both routes get distributed across the backbone:
rather only the best route, as selected by BGP, is distributed. This rather only the best route, as selected by BGP, is distributed. This
precludes load balancing flows across both GWs. precludes load balancing flows across both GWs.
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| Ingress | | Egress ------ | | Ingress | | Egress ------ |
| SR Domain | | SR Domain |Prefix| | | SR Domain | | SR Domain |Prefix| |
| | | | X | | | | | | X | |
| | | ------ | | | | ------ |
| -- | | --- --- | | -- | | --- --- |
| |GW| | | |GW1| |GW2| | | |GW| | | |GW1| |GW2| |
-------++-------- ----+-----------+-+-- -------++-------- ----+-----------+-+--
| \ | / | | \ | / |
| \ | / | | \ | / |
| -+------------- --------+--------+-- | | -+------------- --------+--------+-- |
| ||PE| ----| |---- |PE| |PE| | | | ||ASBR| ----| |---- |ASBR| |ASBR| | |
| | -- |ASBR+------+ASBR| -- -- | | | | ---- |ASBR+------+ASBR| ---- ---- | |
| | ----| |---- | | | | ----| |---- | |
| | | | | | | | | | | |
| | ----| |---- | | | | ----| |---- | |
| | AS1 |ASBR+------+ASBR| AS2 | | | | AS1 |ASBR+------+ASBR| AS2 | |
| | ----| |---- | | | | ----| |---- | |
| --------------- -------------------- | | --------------- -------------------- |
--+-----------------------------------------------+-- --+-----------------------------------------------+--
| |PE| |PE| | | |ASBR| |ASBR| |
| -- AS3 -- | | ---- AS3 ---- |
| | | |
----------------------------------------------------- -----------------------------------------------------
Figure 1: Example Segment Routing Domain Interconnection Figure 1: Example Segment Routing Domain Interconnection
The obvious solution to this problem is to use the BGP feature that The obvious solution to this problem is to use the BGP feature that
allows the advertisement of multiple paths in BGP (known as Add- allows the advertisement of multiple paths in BGP (known as Add-
Paths) [RFC7911] to ensure that all routes to X get advertised by Paths) [RFC7911] to ensure that all routes to X get advertised by
BGP. However, even if this is done, the identity of the GWs will be BGP. However, even if this is done, the identity of the GWs will be
lost as soon as the routes get distributed through an Autonomous lost as soon as the routes get distributed through an Autonomous
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