• BGP topics to be discussed in the next few weeks:

–Excessive route update–Routing instability–BGP policy issues–BGP route slow convergence problem–Interaction between BGP/IGP and among BGP components–Anti-IP-spoofing with BGP–New EGP proposals

BGP Routing Stability of Popular Destinations

Jennifer Rexford, Jia Wang, Zhen Xiao, and Yin Zhang

• Some causes of BGP route changes:– Equipment failures.– Policy changes– Intra-domain topology changes

• Potential problems caused BGP route changes:

• One “event” triggers a long sequence of updates– CPU – Changing paths with traffic can cause congestion

• Transient loops• Make it hard to direct (engineer) the traffic

• What is the current situation:– A large fraction of prefixes have stable BGP

routes– A small fraction of prefixes are responsible for

the majority of Internet traffic

– Are prefixes receiving a large volume of traffic more or less stable than prefixes receiving a lower volume of traffic?

• Intuitively, more traffic can cause more changes

• Popular sites have well managed multiple connections to the Internet.

• How the study is done?– BGP routes and updates in RouteViews and RIPE NCC

are publicly available– This study adds one monitor in the ATT backbone– The anomalies are removed:

• Burst updates due to router failure• Redundant advertisements:

– Multiple updates for the same route– Withdraw before announce

– Updates or events• An event can cause a lot of updates• Routing stability is better reflected by events• How to get events from updates?

– Updates spaced close together in time are counted as one event– This may not be accurate.

• Grouping events: 45seconds/75seconds

• Event duration: mostly < 5 mins

• A small number of prefixes are responsible for most updates events

• Update event vs. traffic volume– Most traffic goes to a small number of prefixes

• Update event vs. traffic volume– Prefixes responsible for most update events do not

receive a lot of traffic

• Explanations:– Unstable prefixes tend to be unpopular

• Unstable BGP routes make it different for other hosts to reach the destinations. They cannot be popular.

• Popular prefixes do not experience many events

• Top websites cause very few update events

• Conclusion:– The majority of the update events are

concentrated in a few prefixes that do not receive much traffic

– Popular sites almost have no updates

– Implications: suppressing updates mostly likely will not cause disruption of the Internet.

• Who are the prefixes that cause most of the updates?• How long does the instability last?• Can we do something about it?