Gateway Auto-Discovery and Route Advertisement for Segment Routing Enabled Data Center Interconnection
draft-drake-bess-datacenter-gateway-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | John Drake , Adrian Farrel , Eric C. Rosen | ||
| Last updated | 2016-06-16 | ||
| Replaced by | draft-ietf-bess-datacenter-gateway, draft-ietf-bess-datacenter-gateway, RFC 9125 | ||
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draft-drake-bess-datacenter-gateway-01
BESS Working Group J. Drake
Internet-Draft A. Farrel
Intended status: Informational E. Rosen
Expires: December 18, 2016 Juniper Networks
June 16, 2016
Gateway Auto-Discovery and Route Advertisement for Segment Routing
Enabled Data Center Interconnection
draft-drake-bess-datacenter-gateway-01
Abstract
Data centers have become critical components of the infrastructure
used by network operators to provide services to their customers.
Data centers are attached to the Internet or a backbone network by
gateway routers and one data center typically has more than one
gateway for commercial, load balancing, and resiliency reasons.
Segment routing is a popular protocol mechanism for operating within
a data center, but also for steering traffic that flows between two
data center sites. In order that one data center site may load
balance the traffic it sends to another data center site it needs to
know the complete set of gateway routers at the remote data center,
the points of connection from those gateways to the backbone network,
and the connectivity across the backbone network.
This document defines a mechanism using the BGP Tunnel Encapsulation
attribute to allow each gateway router to advertise the routes to the
prefixes in the data center site to which it provides access, and
also to advertise on behalf of each other gateway to the same data
center site.
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 RFC 2119 [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 http://datatracker.ietf.org/drafts/current/.
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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
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This Internet-Draft will expire on December 18, 2016.
Copyright Notice
Copyright (c) 2016 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. DC Gateway Auto-Discovery . . . . . . . . . . . . . . . . . . 4
3. Relationship to BGP Link State and Egress Peer Engineering . 5
4. Advertising a DC Route Externally . . . . . . . . . . . . . . 6
5. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Manageability Considerations . . . . . . . . . . . . . . . . 7
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Data centers (DCs) have become critical components of the
infrastructure used by network operators to provide services to their
customers. DCs are attached to the Internet or a backbone network by
gateway routers (GWs) and one DC typically has more than one GW for
various reasons including commercial preferences, load balancing, and
resiliency against connection of device failure.
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Segment routing (SR) [I-D.ietf-spring-segment-routing] is a popular
protocol mechanism for operating within a DC, but also for steering
traffic that flows between two DC sites. In order for an ingress DC
that uses SR to load balance the flows it sends to an egress DC, it
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
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)
instance ([RFC7752] and [I-D.ietf-idr-bgpls-segment-routing-epe]) so
that traffic engineering using SR may be used for these flows.
Suppose that there are two gateways, GW1 and GW2 as shown in
Figure 1, for a given egress DC and they both advertise a route to
prefix X which is located within that DC with 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 both routes do not get
distributed across the backbone, rather only the best route, as
selected by BGP, is distributed. This precludes load balancing flows
across both GWs.
----------------- --------------------
| Ingress | | Egress ------ |
| DC Site | | DC Site |Prefix| |
| | | | X | |
| | | ------ |
| -- | | --- --- |
| |GW| | | |GW1| |GW2| |
-------++--------- ----+----------+-+--
| \ | / |
| \ | / |
| -+------------- --------+-------+-- |
| ||PE| ----| |---- |PE| |PE| | |
| | -- |ASBR+------+ASBR| -- -- | |
| | ----| |---- | |
| | | | | |
| | ----| |---- | |
| | AS1 |ASBR+------+ASBR| AS2 | |
| | ----| |---- | |
| --------------- ------------------- |
--+----------------------------------------------+--
| |PE| |PE| |
| -- AS3 -- |
| |
----------------------------------------------------
Figure 1: Example Data Center Interconnection
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The obvious solution to this problem is to use add-paths
[I-D.ietf-idr-add-paths] to ensure that all routes to X get
advertised by 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 System Border Router (ASBR) that will set itself to be the
next hop. And if there are multiple Autonomous Systems (ASes) in the
backbone, not only will the next hop change several times, but the
add-paths technique will experience scaling issues. This all means
that this approach is limited to DC sites connected over a single AS.
This document defines a solution that overcomes this limitation and
works equally well with a backbone constructed from one or more AS.
This solution uses the Tunnel Encapsulation attribute
[I-D.ietf-idr-tunnel-encaps] as follows:
We define a new tunnel type, "SR tunnel", and when the GWs to a
given DC advertise a route to a prefix X within the DC, they will
each include a Tunnel Encapsulation attribute with multiple tunnel
instances each of type "SR tunnel", one for each GW and each
containing a Remote Endpoint sub-TLV with that GW's address.
In other words, each route advertised by any GW identifies all of the
GWs to the same DC (see Section 2 for a discussion of how GWs
discover each other). Therefore, even if only one of the routes is
distributed to other ASes, it will not matter how many times the next
hop changes, as the Tunnel Encapsulation attribute (and its remote
endpoint sub-TLVs) will remain unchanged.
To put this in the context of Figure 1, GW1 and GW2 discover each
other as gateways for the egress data center site. Both GW1 and GW2
advertise themselves as having routes to prefix X. Furthermore, GW1
includes a Tunnel Encapsulation attribute with a tunnel instance of
type "SR tunnel" for itself and another for GW2. Similarly, GW2
includes a Tunnel Encapsulation for itself and another for GW1. The
gateway in the ingress data center site can now see the possible
paths to the egress data center site and choose one or balance
traffic flows as it sees fit.
2. DC Gateway Auto-Discovery
To allow a given DC's GWs to auto-discover each other and to
coordinate their operations, the following procedures are
implemented:
o Each GW is configured with an identifier for the DC that is common
across all GWs to the DC (i.e., all GWs to all DC sites that are
connected) and unique across all DCs that are connected.
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o A route target ([RFC4360]) is attached to each GW's auto-discovery
route and has its value set to the DC identifier.
o Each GW constructs an import filtering rule to import any route
that carries a route target with the same DC identifier that the
GW itself uses. This means that only these GWs will import those
routes and that all GWs to the same DC will import each other's
routes and will learn (auto- discover) the current set of active
GWs for the DC.
The auto-discovery route each GW advertises consists of the
following:
o An IPv4 or IPv6 NLRI containing one of the GW's loopback addresses
(that is, with AFI/SAFI that is one of 1/1, 2/1, 1/4, 2/4)
o A Tunnel Encapsulation attribute containing the GW's encapsulation
information, which at a minimum consists of an SR tunnel TLV (type
to be allocated by IANA) with a Remote Endpoint sub-TLV as
specified in [I-D.ietf-idr-tunnel-encaps].
To avoid the side effect of applying the Tunnel Encapsulation
attribute to any packet that is addressed to the GW, the GW SHOULD
use a different loopback address.
As described in Section 1, each GW will include a Tunnel
Encapsulation attribute for each GW that is active for the DC site
(including itself), and will include these in every route advertised
externally to the DC site by each GW. As the current set of active
GWs changes (due to the addition of a new GW or the failure/removal
of an existing GW) each externally advertised route will be re-
advertised with the set of SR tunnel instances reflecting the current
set of active GWs.
If a gateway becomes disconnected from the backbone network, or if
the DC operator decides to terminate the gateway's activity, it
withdraws the advertisements described above. This means that remote
gateways at other sites will stop seeing advertisements from this
gateway. It also means that other local gateways at this site will
"unlearn" the removed gateway and stop including a Tunnel
Encapsulation attribute for the removed gateway in their
advertisements.
3. Relationship to BGP Link State and Egress Peer Engineering
When a remote GW receives a route to a prefix X it can use the SR
tunnel instances within the contained Tunnel Encapsulation attribute
to identify the GWs through which X can be reached. It uses this
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information to compute SR TE paths across the backbone network
looking at the information advertised to it in SR BGP Link State
(BGP-LS) [I-D.gredler-idr-bgp-ls-segment-routing-ext] and correlated
using the DC identity. SR Egress Peer Engineering (EPE)
[I-D.ietf-idr-bgpls-segment-routing-epe] can be used to supplement
the information advertised in the BGP-LS.
4. Advertising a DC Route Externally
When a packet destined for prefix X is sent on an SR TE path to a GW
for the DC site containing X, it needs to carry the receiving GW's
label for X such that this label rises to the top of the stack before
the GW complete its processing of the packet. To achieve this we
place a prefix-SID sub-TLV for X in each SR tunnel instance in the
Tunnel Encapsulation attribute in the externally advertised route for
X.
Alternatively, if the GWs for a given DC are configured to allow
remote GWs to perform SR TE through that DC for a prefix X, then each
GW computes an SR TE path through that DC to X from each of the
current active GWs and places each in an MPLS label stack sub-TLV
[I-D.ietf-idr-tunnel-encaps] in the SR tunnel instance for that GW.
5. Encapsulation
If the GWs for a given DC are configured to allow remote GWs send
them a packet in that DC's native encapsulation, then each GW will
also include multiple instances of a tunnel TLV for that native
encapsulation, one for each GW and each containing a remote endpoint
sub-TLV with that GW's address, in externally advertised routes. A
remote GW may then encapsulate a packet according to the rules
defined via the sub-TLVs included in each of the tunnel TLV
instances.
6. IANA Considerations
IANA maintains a registry called "BGP parameters" with a sub-registry
called "BGP Tunnel Encapsulation Tunnel Types." The registration
policy for this registry is First-Come First-Served.
IANA is requested to assign a codepoint from this sub-registry for
"SR Tunnel". The next available value may be used and reference
should be made to this document.
[[Note: This text is likely to be replaced with a specific code point
value once FCFS allocation has been made.]]
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7. Security Considerations
TBD
8. Manageability Considerations
TBD
9. Contributors
The following people contributed to discussions that led to the
development of this document:
TBD
name
Email: email
10. Acknowledgements
Thanks to Bruno Rijsman for review comments, and to Robert Raszuk for
useful discussions.
11. References
11.1. Normative References
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Filsfils, C., Ray, S., Patel, K., Dong, J.,
and M. Chen, "Segment Routing BGP Egress Peer Engineering
BGP-LS Extensions", draft-ietf-idr-bgpls-segment-routing-
epe-05 (work in progress), May 2016.
[I-D.ietf-idr-tunnel-encaps]
Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel
Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-02
(work in progress), May 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<http://www.rfc-editor.org/info/rfc7752>.
11.2. Informative References
[I-D.gredler-idr-bgp-ls-segment-routing-ext]
Previdi, S., Psenak, P., Filsfils, C., Gredler, H., Chen,
M., and j. jefftant@gmail.com, "BGP Link-State extensions
for Segment Routing", draft-gredler-idr-bgp-ls-segment-
routing-ext-02 (work in progress), June 2016.
[I-D.ietf-idr-add-paths]
Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", draft-ietf-idr-
add-paths-15 (work in progress), May 2016.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-08 (work in progress), May 2016.
Authors' Addresses
John Drake
Juniper Networks
Email: jdrake@juniper.net
Adrian Farrel
Juniper Networks
Email: adrian@olddog.co.uk
Eric Rosen
Juniper Networks
Email: erosen@juniper.net
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