draft-ietf-rtgwg-bgp-pic-01.txt   draft-ietf-rtgwg-bgp-pic-02.txt 
Network Working Group A. Bashandy, Ed. Network Working Group A. Bashandy, Ed.
Internet Draft C. Filsfils Internet Draft C. Filsfils
Intended status: Informational Cisco Systems Intended status: Informational Cisco Systems
Expires: December 2016 P. Mohapatra Expires: February 2017 P. Mohapatra
Sproute Networks Sproute Networks
June 20, 2016 August 1, 2016
BGP Prefix Independent Convergence BGP Prefix Independent Convergence
draft-ietf-rtgwg-bgp-pic-01.txt draft-ietf-rtgwg-bgp-pic-02.txt
Abstract Abstract
In the network comprising thousands of iBGP peers exchanging millions In the network comprising thousands of iBGP peers exchanging millions
of routes, many routes are reachable via more than one next-hop. of routes, many routes are reachable via more than one next-hop.
Given the large scaling targets, it is desirable to restore traffic Given the large scaling targets, it is desirable to restore traffic
after failure in a time period that does not depend on the number of after failure in a time period that does not depend on the number of
BGP prefixes. In this document we proposed an architecture by which BGP prefixes. In this document we proposed an architecture by which
traffic can be re-routed to ECMP or pre-calculated backup paths in a traffic can be re-routed to ECMP or pre-calculated backup paths in a
timeframe that does not depend on the number of BGP prefixes. The timeframe that does not depend on the number of BGP prefixes. The
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documents at any time. It is inappropriate to use Internet-Drafts documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in as reference material or to cite them other than as "work in
progress." progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html http://www.ietf.org/shadow.html
This Internet-Draft will expire on December 20, 2016. This Internet-Draft will expire on December 1, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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speaker has a path for. speaker has a path for.
o IGP prefix: It is a prefix P/m (of any AFI/SAFI) that is learnt o IGP prefix: It is a prefix P/m (of any AFI/SAFI) that is learnt
via an Interior Gateway Protocol, such as OSPF and ISIS, has a via an Interior Gateway Protocol, such as OSPF and ISIS, has a
path for. The prefix may be learnt directly through the IGP or path for. The prefix may be learnt directly through the IGP or
redistributed from other protocol(s) redistributed from other protocol(s)
o CE: It is an external router through which an egress PE can o CE: It is an external router through which an egress PE can
reach a prefix P/m. reach a prefix P/m.
o Ingress PE, "iPE": t is a BGP speaker that learns about a prefix o Ingress PE, "iPE": It is a BGP speaker that learns about a prefix
through a IBGP peer and chooses an egress PE as the next-hop for through a IBGP peer and chooses an egress PE as the next-hop for
the prefix.. the prefix..
o Path: It is the next-hop in a sequence of unique connected o Path: It is the next-hop in a sequence of unique connected
nodes starting from the current node and ending with the nodes starting from the current node and ending with the
destination node or network identified by the prefix. destination node or network identified by the prefix.
o Recursive path: It is a path consisting only of the IP address o Recursive path: It is a path consisting only of the IP address
of the next-hop without the outgoing interface. Subsequent of the next-hop without the outgoing interface. Subsequent
lookups are needed to determine the outgoing interface. lookups are needed to determine the outgoing interface.
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longer a dependent/child of object Y longer a dependent/child of object Y
o Route: It is a prefix with one or more paths associated with o Route: It is a prefix with one or more paths associated with
it. Hence the minimum set of objects needed to construct a it. Hence the minimum set of objects needed to construct a
route is a leaf and a pathlist. route is a leaf and a pathlist.
2. Overview 2. Overview
The idea of BGP-PIC is based on two pillars The idea of BGP-PIC is based on two pillars
o A shared hierarchal Forwarding Chain o A shared hierarchical Forwarding Chain
o A forwarding plane that supports multiple levels of indirection o A forwarding plane that supports multiple levels of indirection
To illustrate the two pillars above, we will use an example of a To illustrate the two pillars above, we will use an example of a
simple multihomed L3VPN [8] prefix in a BGP-free core running LDP simple multihomed L3VPN [8] prefix in a BGP-free core running LDP
[5] or segment routing over MPLS forwarding plane [14]. [5] or segment routing over MPLS forwarding plane [14].
+--------------------------------+ +--------------------------------+
| | | |
| ePE2 | ePE2
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|VPN-L12 (VPN-IP1, NH2)| |IGP-L12 (IGP-IP1, NH2)| |VPN-L12 (VPN-IP1, NH2)| |IGP-L12 (IGP-IP1, NH2)|
+----------------------+ +----------------------+ +----------------------+ +----------------------+
Figure 2 Shared Hierarchical Forwarding Chain at iPE Figure 2 Shared Hierarchical Forwarding Chain at iPE
The forwarding chain depicted in Figure 2 illustrates the first The forwarding chain depicted in Figure 2 illustrates the first
pillar, which is sharing and hierarchy. We can see that the BGP pillar, which is sharing and hierarchy. We can see that the BGP
pathlist consisting of BGP-NH1 and BGP-NH2 is shared by all NLRIs pathlist consisting of BGP-NH1 and BGP-NH2 is shared by all NLRIs
reachable via ePE1 and ePE2. As such, it is possible to make changes reachable via ePE1 and ePE2. As such, it is possible to make changes
to the pathlist without having to make changes to the NLRIs. For to the pathlist without having to make changes to the NLRIs. For
example, if BGP-NH2 becomes unreacreachable, there is no need to example, if BGP-NH2 becomes unreachable, there is no need to modify
modify any of the possibly large number of NLRIs. Instead only the any of the possibly large number of NLRIs. Instead only the shared
shared pathlist needs to be modified. Likewise, due to the pathlist needs to be modified. Likewise, due to the hierarchical
hierarchical structure of the forwarding chain, it is possible to structure of the forwarding chain, it is possible to make
make modifications to the IGP routes without having to make any modifications to the IGP routes without having to make any changes
changes to the BGP NLRIs. For example, if the interface "I2" goes to the BGP NLRIs. For example, if the interface "I2" goes down, only
down, only the shared IGP pathlist needs to be updated, but none of the shared IGP pathlist needs to be updated, but none of the IGP
the IGP prefixes sharing the IGP pathlist nor the BGP NLRIs using prefixes sharing the IGP pathlist nor the BGP NLRIs using the IGP
the IGP prefixes for resolution need to be modified. prefixes for resolution need to be modified.
Figure 2 can also be used to illustrate the second BGP-PIC pillar. Figure 2 can also be used to illustrate the second BGP-PIC pillar.
Having a deep forwarding chain such as the one illustrated in Figure Having a deep forwarding chain such as the one illustrated in Figure
2 requires a forwarding plane that is capable of accessing multiple 2 requires a forwarding plane that is capable of accessing multiple
levels of indirection in order to calculate the outgoing levels of indirection in order to calculate the outgoing
interface(s) and next-hops(s). While a deeper forwarding chain interface(s) and next-hops(s). While a deeper forwarding chain
minimizes the re-convergence time on topology change, there will minimizes the re-convergence time on topology change, there will
always exist platforms with limited capabilities and hence imposing always exist platforms with limited capabilities and hence imposing
a limit on the depth of the forwarding chain. The example in Section a limit on the depth of the forwarding chain. The example in Section
3.2 illustrates how to gracefully trade off convergence speed with 3.2 illustrates how to gracefully trade off convergence speed with
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