• 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?