On Understanding of Transient Interdomain Routing Failures

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On Understanding of Transient Interdomain Routing
Failures

• Feng Wang, Lixin Gao, Jia Wang, and Jian Qiu

Department of Electrical and Computer Engineering
University of Massachusetts, Amherst MA 01002
ATT Labs-research 180 Park Ave, Florham Park NJ
07869
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Outline

• What is transient routing failures?
• When can transient routing failures occur?
• How long can transient routing failures last?
• Measurement results

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Internet Routing

• Autonomous systems (ASes)
• Internet Service Providers (ISPs)
• Companies
• Universities
• Intradomain Routing Protocols
• Static Routing, OSPF, IS-IS
• Interdomain Routing Protocol
• Border Gateway Protocol (BGP)

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Long Convergence Delay

• Long convergence delay (Labovitz et al, TON2001)
• Bringing a route back
• (Tup) ltshortest path length ? MRAI
• Disconnecting a route
• (Tdown) ltlongest path length ? MRAI
• Fail-over rerouting from Path A to Path B
• During the time for discovering Path B, routers
  might experience transient routing failures,
  i.e., no route is available

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An Example of Transient Routing Failure
AS3
AS1
W20
W20
W20
AS2
120 10
10
20
210
A10
A10
A10
losing reachability
Traffic on data plane
AS0
BGP update
d
BGP Routing table
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Our Contributions

• Identify transient routing failures
• Sufficient conditions
• Bound transient routing failure duration

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Outline

• What is transient routing failures?
• When can transient routing failures occur?
• How long can transient routing failures last?
• Measurement results

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When Transient Routing Failures can Occur?

• Two sufficient conditions for a node must
  experience a transient routing failure (transient
  routing failure for sure).
• One sufficient condition for a node may
  experience a transient routing failure (potential
  transient routing failure).

w
10
310

1
3
w
2
210 20
20
0
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When Transient Routing Failures can Occur?
(contd.)
w
310 320
320
10
310
1
3
w
A
2
210 20
20
0
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Outline

• What is transient routing failures?
• When can transient routing failures occur?
• How long can transient routing failures last?
• Measurement results

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How long Transient Routing Failures last?
MRAI timer
MRAI timer
W 2 0
W 2 0
W 2 0
120 10
10
10
210
2
1
A 10
A 10
A 10
0
d
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MRAI Timers

• Minimum Advertisement Interval timer
• Minimum amount of time that must elapse between
  routing updates
• Applied to BGP announcement or withdrawal
• Default MRAI value
• eBGP session 30 seconds
• iBGP session 5 seconds

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Upper Bound for Transient Routing Failure Duration

• Transient routing failure ? min(du? d ?u ) ?
  MRAI

du?
, d?u
?
u
u
?
v
0
0
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Transient Failures in a Typical BGP System

• A typical BGP system means that every router in
  the system applies common routing policies.
• Routing policies are guided by commercial
  relationships between ASes.
• Customer-to-provider
• Peer-to-peer
• Common routing policies
• Import policies are guided by the prefer-customer
  routing policies.
• Export policies are guided by the no-valley
  routing policies

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Occurrence of Transient failures in a typical BGP
system

• In a typical BGP system, transient failures are
  prevalent.
• Tier-1 ASes can experience transient routing
  failures, where alternate routes come from their
  edge routers.
• Non tier-1 ASes can experience transient routing
  failures, where alternate routes are obtained
  from other ASes.

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Outline

• What is transient routing failures?
• When can transient routing failures occur?
• How long can transient routing failures last?
• Measurement results

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Measuring Transient Failures within a tier-1 AS
BGP updates, BGP tables and router configuration
files are collected during July 2004
Cumulative distribution of transient Failure
Duration
Percentage of transient failures among all
routing failures that last less than 30 seconds
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Measuring Transient Failures contd.

• Transient failures in tier-2 ASes using Oregon
  RouteViews BGP updates (July 2004)

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Popularity of Prefixes Experiencing Transient
Failures

• We aggregate the Netflow data collected in the
  tier-1 AS during the week (1/2/20051/8/2005)
• Transient routing failures can impact on popular
  prefixes and unpopular prefixes

Fraction of transient routing failures
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Conclusions

• Transient routing failures are prevalent in the
  Internet, and can last for a significant period
  of time.
• Majority of transient failures occur under the
  commonly applied routing policy setting.
• Popular and unpopular prefixes can experience
  transient failures.

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Thanks