Internet DRAFT - draft-ietf-grow-simple-va
draft-ietf-grow-simple-va
GROW Working Group R. Raszuk
Internet-Draft NTT MCL
Intended status: Informational J. Heitz
Expires: February 17, 2013 Ericsson
A. Lo
Arista
L. Zhang
UCLA
X. Xu
Huawei
August 16, 2012
Simple Virtual Aggregation (S-VA)
draft-ietf-grow-simple-va-12.txt
Abstract
All BGP routers in the Default Free Zone (DFZ) are required to carry
all the routes in the Default Free Routing Table (DFRT). A technique
is described that allows some BGP routers not to install all of those
routes into the Forwarding Information Base (FIB).
Some routers in an Autonomous System (AS) announce an aggregate (the
VA prefix) in addition to the routes they already announce. This
enables other routers not to install the routes covered by the VA
prefix into the FIB as long as those routes have the same next-hop as
the VA prefix.
The VA prefixes that are announced within an AS are not announced to
any other AS. Described functionality is of very low operational
complexity by proposing a confined BGP speaker solution without any
dependency on network wide configuration or requirement for any form
of intra-domain tunneling.
Status of this Memo
This Internet-Draft is submitted to IETF 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
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Drafts is at http://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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 17, 2013.
Copyright Notice
Copyright (c) 2012 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope of this Document . . . . . . . . . . . . . . . . . . 4
1.2. Requirements notation . . . . . . . . . . . . . . . . . . . 4
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Operation of S-VA . . . . . . . . . . . . . . . . . . . . . . . 5
3. Deployment considerations . . . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
A technique called Simple Virtual Aggregation (S-VA) is described.
It allows some routers not to have to store some routes in the
Forwarding Information Base (FIB) while still advertising and
receiving the full Default Free Routing Table (DFRT) in BGP.
A typical scenario is as follows. Core routers in the ISP maintain
the full DFRT in the FIB and RIB. Edge routers maintain the full
DFRT in the BGP Loc-RIB, but do not install certain routes in the RIB
and FIB. Edge routers may install a default route to core routers,
to Area Border Routers (ABR) which are installed on the Point of
Presence (POP), to core boundary routers or to Autonomous System
Border Routers (ASBR).
S-VA must be enabled on an edge router that needs to save its RIB and
FIB space. The core routers must announce a new prefix called
virtual aggregate (VA prefix).
1.1. Scope of this Document
The VA prefix is not intended to be announced from one AS into
another, only between routers of the same AS.
S-VA can be used for IPv4 and IPv6 both unicast and multicast address
families.
S-VA does not need to operate on on every router in an AS.
1.2. Requirements notation
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].
1.3. Terminology
RIB/FIB-Installing Router (FIR): A router that does not suppress any
routes and announces the VA prefix. Typically a core router, a
POP to core boundary router or an ASBR would be configured as an
FIR.
RIB/FIB-Suppressing Router (FSR): An S-VA router that installs the
VA prefix, and does not install into its FIB routes that are
covered by and have the same next-hop as the VA prefix. Typically
an edge router would be configured as an FSR.
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Suppress: Not to install a route that is covered by the VA prefix
into the global RIB or FIB.
Legacy Router: A router that does not run S-VA, and has no knowledge
of S-VA.
Global Routing Information Base (RIB): All the routing protocols in
a router install their selected routes into the RIB. The routes
in the RIB are used to resolve next-hops for other routes, to be
redistributed to other routing protocols and to be installed into
the FIB.
Local/Protocol Routing Information Base (Loc-RIB): The Loc-RIB
contains the routes that have been selected by the local BGP
speaker's Decision Process as in [RFC4271].
NLRI: Network Layer Reachability Information [RFC4271]
2. Operation of S-VA
There are three types of routers in S-VA, FIB-Installing routers
(FIR), FIB-Suppressing routers (FSR) and optionally, legacy routers.
While any router can be an FIR or an FSR, the simplest form of
deployment is for AS border routers to be configured as FIRs and for
customer facing edge routers to be configured as FSRs.
When a FIR announces a VA prefix, it sets the path attributes as
follows: The ORIGIN MUST be set to INCOMPLETE (value 2). The
NEXT_HOP MUST be set to the same as that of the routes which are
intended to be covered by the VA prefix. The ATOMIC_AGGREGATE and
AGGREGATOR attributes SHOULD NOT be included. The FIR MUST attach a
NO_EXPORT Community Attribute [RFC1997]. The NLRI SHOULD be 0/0.
A FIR SHOULD NOT FIB-suppress any routes.
An FSR must detect the VA prefix or prefixes (including 0/0) and
install them in all of Loc-RIB, RIB and FIB. The FSR MAY suppress
any more specific routes that carry the same next-hop as the VA
prefix.
Generally, any more specific route which carries the same next-hop as
the VA prefix is eligible for suppression. However, provided that
there is at least one less specific prefix with different next-hop
between the VA prefix and the suppressed prefixes then those
suppressed prefixes must be reinstalled.
An example with 3 prefixes can be considered, where the VA-prefix
(prefix 1) is the least specific and covers prefix 2 and prefix 3.
Prefix 2 is less specific than prefix 3 and covers the latter. If
all three have the same next-hop, then only the bigger one, i.e. VA-
Prefix, is announced. However, if prefix 2 has a different next-hop,
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then it will need to be announce separately. In this case, it is
important to also announce prefix 3 separately.
Similarly, when IBGP multipath is enabled and when multiple VA
prefixes form a multipath, only those more specific prefixes of which
the set of next-hops are identical to the set of next-hops of the VA
prefix multipath are subject to suppression.
The expected behavior is illustrated in Figure 1. This figure shows
an autonomous system with a FIR FIR1 and an FSR FSR1. FSR1 is an
ASBR and is connected to two external ASBRs, EP1 and EP2.
+------------------------------------------+
| Autonomous System | +----+
| | |EP1 |
| /---+---| |
| To ----\ +----+ +----+ / | +----+
| Other \|FIR1|----------|FSR1|/ |
|Routers /| | | |\ |
| ----/ +----+ +----+ \ | +----+
| \---+---|EP2 |
| | | |
| | +----+
+------------------------------------------+
Figure 1
Suppose that FSR1 has been enabled to perform S-VA. Originally it
receives all routes from FIR1 (doing next-hop-self) as well as from
EP1 and EP2. FIR1 now will advertise a VA prefix 0/0 with next-hop
set to itself. That will cause FSR1 to suppress all routes with the
same next-hop as the VA prefix. However, FSR1 will not suppress any
routes received from EP1 and EP2, because their next-hops are
different from that of the VA prefix.
Several FIRs may announce different S-VA prefixes. For example, in a
POP, each edge router can announce into the POP an S-VA prefix that
covers the addresses of the customers it services.
Several FIRs may announce the same S-VA prefix. In this case an FSR
must choose to install only one of them. For example, two redundant
ASBRs, both of which announce the complete DFRT may each also
announce the default route as an S-VA prefix into the AS.
S-VA may be used to split traffic among redundant exit routers. For
example, referring to Figure 1, suppose EP1 and EP2 are two redundant
ASBRs that announce the complete DFRT. Each may also announce two
S-VA prefixes into the AS: 0/1 and 128/1. EP1 might announce 0/1
with higher preference and EP2 might announce 128/1 with higher
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preference. FIR1 will now install into its FIB 0/1 pointing to EP1
and 128/1 pointing to EP2. If either one of EP1 or EP2 were to fail,
then FSR1 would switch the traffic to the other exit router with a
single FIB installation of one S-VA prefix.
3. Deployment considerations
BGP routes may be used to resolve next-hops for static routes or
other BGP routes. Because the default route does not imply
reachability of any destination, a router can be configured not to
resolve next-hops using the default route. In this case, S-VA should
not suppress from installation into the RIB a route that may be used
to resolve a next-hop for another route. It may still suppress it
from installation into the FIB.
Selected BGP routes in the RIB may be redistributed to other
protocols. If they no longer exist in the RIB, they will not be
redistributed. This is especially important when the conditional
redistribution is taking place based on the length of the prefix,
community value etc. In those cases where redistribution policy is
in place S-VA implementation should refrain from suppressing
installation into the RIB routes matching such policy. It may still
suppress them from installation into the FIB.
A router may originate a network route or an aggregate route into
BGP. Some addresses covered by such a route may not exist. If this
router were to receive a packet for an unreachable address within an
originated route, it must not send that packet to the VA prefix
route. There are several ways to achieve this. One is to have the
FIR aggregate the routes instead of the FSR. Another is to install a
blackhole route for the nonexistent addresses on the originating
router. This issue is not specific to S-VA, but applicable to the
general use of default routes.
Like any aggregate, an S-VA prefix may include more address space
than the sum of the prefixes it covers. As such, the S-VA prefix may
provide a route for a packet for which no real destination exists.
An FSR will forward such a packet to the FIR.
If an S-VA prefix changes its next-hop or is removed, then many
routes may need to be downloaded into the FIB to achieve convergence.
4. IANA Considerations
There are no IANA considerations.
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5. Security Considerations
The authors are not aware of any new security considerations due to
S-VA. The local nature of the proposed optimization eliminates any
external exposure of the functionality. The presence of more
specifics which are used as VA prefixes is also a normal BGP
behaviour in current networks.
6. Acknowledgements
The concept for Virtual Aggregation comes from Paul Francis. In this
document authors only simplified some aspects of its behavior to
allow simpler adoption by some operators.
Authors would like to thank Clarence Filsfils, Nick Hilliard, S.
Moonesamy and Tom Petch for their review and valuable input.
7. Normative References
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
Authors' Addresses
Robert Raszuk
NTT MCL
101 S Ellsworth Avenue Suite 350
San Mateo, CA 94401
US
Email: robert@raszuk.net
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Jakob Heitz
Ericsson
300 Holger Way
San Jose, CA 95135
USA
Phone:
Email: jakob.heitz@ericsson.com
Alton Lo
Arista Networks
5470 Great America Parkway
Santa Clara, CA 95054
USA
Phone:
Email: altonlo@aristanetworks.com
Lixia Zhang
UCLA
3713 Boelter Hall
Los Angeles, CA 90095
US
Phone:
Email: lixia@cs.ucla.edu
Xiaohu Xu
Huawei Technologies
No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District
Beijing, Beijing 100085
P.R.China
Phone: +86 10 82836073
Email: xuxh@huawei.com
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