BGP Path exploration

1
A Variation of Route Flap Damping to Improve BGP
Routing Convergence
Wang Lijun, Wu Jianping, Xu Ke Department of
Computer Science and Technology, Tsinghua
University
Simulation Results
Neighboring nodes suppression
Problems of Inter-domain routing convergence

• BRITE generated, heavy- tailed topology

• Useless RFD operation on remote nodes

• BGP Path exploration

• Convergence time comparision

• Neighboring nodes insert a Mark after apply RFD
  to a route change, remote nodes do not need to
  apply RFD to the route change.

• BGP is a path vector protocol

• After fail down event, BGP speaker explores
  invalid routes

• Suppression Mark does not solve instable BGP
  session

• Communication overhead comparision

• Interaction of RFD with path exploration

• Apply RFD to route change resulting from broken
  BGP session

• Partial deployment

Multiple invalid routes make RFD suppress
relative route falsely

• General design goal

• Relative stable routes converge immediately
• Flapping routes undergo suppression and converge
  fast after being released
• Reduce communication overhead during routing
  convergence
• Compatible with traditional Route Flap Damping
  mechanism

2 flap
Invalid routes suppression

• Characteristics of invalid routes

• The interval between successive invalid routes is
  MRAI
• Maximal duration of path exploration is MRAIn, n
  is the longest AS path
• Route attributes, especially AS_PATH, are changed
• LOCAL_PREF of successive invalid routes decrease
  monotonously

Main idea of design
4 flap

• Classify route change according different causes
• Network event, e.g. link/interface down
• Resulting from BGP protocol behavior
• Apply different mechanism
• How to differentiate route change of different
  causes ? ? ?

• Processing of Invalid routes

• Coexist with traditional RFD

Overview of the design

• Penalize attribute change more than Withdrawal
• The penalty of routes which are not suppressed
  decays exponentially, with half life is MRAI
• If a suppressed route keeps stable for kMRAI,
  release the route
• if suppressed routes changes, just reset the
  reuse timer

2 flap


Receive Update
Judge cause
Algorithm of modified RFD
BGP session broken ?
BGP protocol behavior ?
Suppression Mark ?
4 flap

Apply RFD

Invalid routes suppression

• Add Suppression Mark in BGP Update as an
  attribute
• Apply Invalid routes suppression to Update arise
  from BGP protocol behavior