Sufficient Conditions to Guarantee Path Visibility

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Sufficient Conditions to Guarantee Path Visibility
Akeel ur Rehman Faridee 2005-03-0021
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The Internet (General Picture)
End-hosts
Routers
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The Internet (Original Picture)
Internet is actually divided into different
Autonomous Systems (ASs), governed by different
organization entities.
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Autonomous Systems (ASes)
An autonomous system is a region of the Internet
that is administered by a single entity and that
has a unified routing policy
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Interdomain vs Intradomain
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What Problem is BGP Solving?
Reachability Information
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BGP
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Two Flavors of BGP

• External BGP (eBGP) exchanging routes between
  ASes
• Internal BGP (iBGP) disseminating routes to
  external destinations among the routers within an
  AS

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Two flavors?

• Most ASes have more than one border router that
  talks to other peers
• Must disseminate information inside the AS and
  through the AS.
• Must have complete visibility.

COMPLETE VISIBILITY For every external
destination, each router picks the same route
that it would have picked had it seen the best
routes from each eBGP router in the AS.
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iBGP
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iBGP Mesh Does Not Scale
eBGP update

• N border routers means N(N-1)/2 peering sessions
• Each router must have N-1 iBGP sessions
  configured
• Size of iBGP routing table can be order N larger
  than number of best routes (remember alternate
  routes!)
• Each router has to listen to update noise from
  each neighbor

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Problems with Route Reflectors
Lack of complete visibility every router is not
guaranteed to see its best available route.
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Route Reflectors
RR

• Route reflectors can pass on iBGP updates to
  clients
• Each RR passes along ONLY best routes
• ORIGINATOR_ID and CLUSTER_LIST attributes are
  needed to avoid loops

RR
RR
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BGP Blackhole
A missing iBGP session can create network
partition even the underlying IP topology is
connected.
A missing iBGP session might keep one router from
receiving route information for some prefixes,
making it a blackhole for that prefix.
Knowing the sufficient conditions to gaurantee
the VISIBILITY of all available path to prevent
the blackhole, both in case of partitions and
common case, is of greater interset.
Blackhole A router that drops all the packets of
a particular prefix (because it doesnt have the
reachability information for this prefix) is
called the black hole for this prefix.
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Selected BGP RFCs
http//www.ietf.org
Internet Engineering Task Force (IETF)

• IDR http//www.ietf.org/html.charters/idr-charte
  r.html
• RFC 1771 A Border Gateway Protocol 4 (BGP-4)
• RFC 1772 Application of the Border Gateway
  Protocol in the Internet
• RFC 1773 Experience with the BGP-4 protocol
• RFC 1774 BGP-4 Protocol Analysis
• RFC 2796 BGP Route Reflection An alternative to
  full mesh IBGP
• RFC 3065 Autonomous System Confederations for BGP
  

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Acknowledgements
Some of the slides/figures are taken from Hari
Balakrishnan and Nick Feamster website.
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References
1 Hari Balakrishnan, 2001-2005, and Nick
Feamster, Chapter 4 Interdomain Internet
Routing, 2005, http//nms.csail.mit.edu/6.829-
f05/lectures/L4-routing.pdf 2 M Vutukuru, P
Valiant, S Kopparty, Hari Balakrishnan How to
Construct a correct and Scalable iBGP
Confuguration, Proceedings of IEEE INFOCOM,
2006 3 T. Bates, R. Chandra, and E. H. Chen.
BGP Route Reflection An Alternative to
Full Mesh iBGP, April 2000 4 Timothy Griffin
and Gordon T. Wilfong. On the Correctness of iBGP
Configuration. In Proc. ACM SIGCOM, pages
17-29, Pittsburgh, PA, August 2002 5 FEAMSTER,
N., AND BALAKRISHNAN, H. Verifying the
correctness of wide- area Internet routing.
Tech. Rep. MIT-LCS-TR-948, Massachusetts Inst. of
Tech., May 2004 6 Nick Feamster, Jared
Winick, and Jennifer Rexford. A Model of BGP
Routing for Network Engineering. In ACM
Sigmetrics - Performance 2004, New York, NY,
June 2004.