Download griffin-BGPConvTime

An Experimental Analysis of
BGP Convergence Time
Timothy Griffin AT&T Research
& Brian Premore Dartmouth College
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The problem
• There is a considerable delay in BGP
convergence after a route change.
• The configurations on the
autonomous system (AS) routers
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Solution
• By simulating a set of different
router configurations,
– find the optimal configuration in which
the convergence time is minimal.
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Importance
• There is a considerable convergence
delay after a route change
• Before the network converges
– packet loss
– packet delay
– disruption of connectivity
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Roadmap
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BGP routing & reasons for long
convergence time
Some configurable options in BGP level
routers
Simulation network settings
Analysis options vs. convergence time
Summary
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BGP routing

How BGP routing work


distance-vector algorithm
Two types of update messages
 Advertisements
 withdrawals
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Long convergence time

Nature of BGP path selection
 Routers
enumerate multiple paths
 Eliminate and replacing other choices

Minimum Route Advertisement Interval
 MRAI,
usually 30 seconds (hardcode)
 Add delays

Not guaranteed converge!!
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Roadmap





BGP routing & reasons for long
convergence time
Some configurable options in BGP level
routers
Simulation network settings
Analysis options vs. convergence time
Summary
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Router configurations

MRAI
–
–
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SSLD
–
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Sender side loop detection
WRATE
–
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Too high: longer delay between update message
Too low: oscillation of update message among
routers  more update messages
Withdrawal rate limiting
Observations

Depend on the network …
–
–
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The affects of not using optimal value of MRAI
–

Very similar for all networks
The affect of using SLLD and WRITE
–
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There is an optimal value of MRAI to minimize the number
of update messages needed to be sent
There is another optimal value of MRAI to minimize the
convergence time
Good and bad depends on the networks
optimal values of MRAI

number of update/withdrawal messages sent
–
–

the convergence time
–
–
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MRAI small, oscillation
MRAI large …
MRAI small …
MRAI large, longer to wait between messages
using non-optimal MRAI


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Increase rapidly for MRAI < optimal
Increase linearly for MRAI > optimal
Roadmap





BGP routing & reasons for long
convergence time
Some configurable options in BGP level
routers
Simulation network settings
Analysis options vs. convergence time
Summary
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Simulation setting

SSFNet
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

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Networks

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
Java-based simulation package
IP-level
BGP-4 supported natively
Simple topology
 CLIQUE, CHAIN, RING, FOCUS, P-CLIQUE
Limited size (5-20 nodes)
Combinations of MRAI values, SSLD & WRATE

Perl script, >200,000 runs, >1 week
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More on simulation setting
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One AS is one node in the network
Only a single link update or withdrawal each time
All routers have the same configurations
No commercial extension
Using network which guaranteed converge
Random delays on processing route updates
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Roadmap





BGP routing & reasons for long
convergence time
Some configurable options in BGP level
routers
Simulation network settings
Analysis options vs. convergence time
Summary
16
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Roadmap





BGP routing & reasons for long
convergence time
Some configurable options in BGP level
routers
Simulation network settings
Analysis options vs. convergence time
Summary
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Conclusion
 We can configure the MRAI on BGP
level routers to minimize convergence
time.
 The optimal value depends on the
network
 Having a higher MRAI value tends to
be safer
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Future work
 We know there is a optimal settings
 It depends on topology, link changes, …
 How can we configure the routers so the
convergence time is close to the optimal
value?
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