Post on 03-Jan-2016
• 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?