preventing the unnecessary propagation of bgp withdraws · v. van den schrieck - networking 2009...
TRANSCRIPT
Networking 2009, May 13th
Preventing the unnecessary propagation
of BGP withdraws
V. Van den Schrieck, P. François, C. Pelsser, O.Bonaventurehttp://inl.info.ucl.ac.be
V. Van den Schrieck - Networking 2009
Agenda
• Introduction
• Presentation and evaluation of iBGP-caused withdraws
• Preventing iBGP-caused withdraws
✓ Advertising more than one path in iBGP (IETF)
✓ Our proposal : Advertising the availability of alternate paths in iBGP
2
V. Van den Schrieck - Networking 2009
Agenda
• Introduction
• Presentation and evaluation of iBGP-caused withdraws
• Preventing iBGP-caused withdraws
✓ Advertising more than one path in iBGP (IETF)
✓ Our proposal : Advertising the availability of alternate paths in iBGP
3
V. Van den Schrieck - Networking 2009
BGP, the glue of the Internet
• Border Gateway Protocol - Interdomain routing protocol used in the Internet
• Exchange paths to destinations between Autonomous Systems (AS)
✓ Each router advertises its best path to its BGP peers
✓ Selection process : Several rules
• A path is described by the AS Path, i.e. the sequence of AS that leads to the path destination
4
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6> P : local
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6
P : 1
P : 1
> P : local
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6> P : local
> P : 1
> P : 1
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6> P : local
P : 3 1 > P : 1
> P : 1
P : 2 1
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6> P : local
> P : 3 1> P : 1
> P : 1
> P : 2 1
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6> P : local
> P : 3 1> P : 1
> P : 1
> P : 2 1 P : 4 3 1
P : 5 2 1
P : 5 2 1
V. Van den Schrieck - Networking 2009
BGP
5
P
AS1
AS3
AS4
AS2
AS5
AS6> P : local
> P : 3 1> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 3 1 P : 5 4 3 1
V. Van den Schrieck - Networking 2009
iBGP vs eBGP
• An Autonomous System has several routers
• All routers of an AS need to learn the paths to all destination advertised to the AS
✓ BGP sessions between routers of the AS : iBGP
- Specific iBGP rule : Do not advertise an iBGP-received path on an iBGP session
- Exception : Route Reflectors
✓ BGP sessions between routers of different AS : eBGP
6
V. Van den Schrieck - Networking 2009
iBGP vs eBGP
7
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
V. Van den Schrieck - Networking 2009
Agenda
• Introduction
• Presentation and evaluation of iBGP-caused withdraws
• Preventing iBGP-caused withdraws
✓ Advertising more than one path in iBGP (IETF)
✓ Our proposal : Advertising the availability of alternate paths in iBGP
8
V. Van den Schrieck - Networking 2009
BGP Churn
• Churn is one of today’s BGP issues
• Churn : High number of unnecessary BGP messages
✓ Unnecessary : Do not impact the final routing state
• Consequences :
✓ Load on router’s CPU
✓ Transient losses of reachability
9
V. Van den Schrieck - Networking 2009
BGP Churn
10
http://bgpupdates.potaroo.net/instability/bgpupd.html
• Average daily number of BGP updates : 400.000
V. Van den Schrieck - Networking 2009
Origin of BGP churn
• Path exploration during BGP convergence
• Flapping prefixes
• Bad iBGP propagation
✓ Routers without path diversity could send unnecessary BGP withdraws in case of failure
✓ Even tough alternate paths exist in the AS
11
V. Van den Schrieck - Networking 2009
Bad iBGP propagation
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
2 paths
1 path
V. Van den Schrieck - Networking 2009
Origins of bad iBGP propagation
• Only best path announced on iBGP sessions
• One path preferred over all others => alternate paths are never propagated
✓ Path quality (AS path length)
✓ BGP policies (Local preference)
• Complex iBGP organizations
✓ Paths hidden by Route Reflectors
13
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
> P : 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
W(P)
> P : 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
W(P)
W(P)
> P : 2 1
> P : 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
W(P)
W(P)
> P : 2 1
> P : 1> P : 5 2 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1> P : 5 2 1
> P : 2 1 P : 4 3 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1> P : 5 2 1
> P : 2 1 P : 4 3 1 P : 2 1 > P : 4 3 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1> P : 5 2 1
> P : 2 1 P : 4 3 1 P : 2 1 > P : 4 3 1
P : 4 3 1
W(P)
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1> P : 5 2 1
> P : 2 1 P : 4 3 1 P : 2 1 > P : 4 3 1
P : 2 1> P : 4 3 1
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1> P : 5 2 1
> P : 2 1 P : 4 3 1 P : 2 1 > P : 4 3 1
P : 2 1> P : 4 3 1
P : 5 4 3 1
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009
Withdraw Propagation when alternate path exists
14
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1
> P : 1> P : 5 2 1
> P : 2 1 P : 4 3 1 P : 2 1 > P : 4 3 1
P : 2 1> P : 4 3 1
P : 5 4 3 1
> P : 5 4 3 1
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009
Quantification of unnecessary iBGP-caused Withdraws
• RouteViews Dataset : BGP feeds of parallel sessions (2 sessions with the same AS)
• Withdraw defined as iBGP-caused if the destination is withdrawn on one session, but stay stable on the other during 30 seconds before and after
• Withdraw is unnecessary because an alternate path exists in the AS
AS X
RouteView Collector
W (D)
15
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2 W(P)
W(P)
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2 W(P)
W(P)
Withdraw detected=> start timer
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2
Withdraw detected
P : 2> P : 3 4
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2
Withdraw detected
P : 2> P : 3 4
P : 1 3 4
P : 3 4
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2
Withdraw detected
P : 2> P : 3 4 P : 2
> P : 3 4
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2
Withdraw detected
P : 2> P : 3 4 P : 2
> P : 3 4
P : 1 3 4
V. Van den Schrieck - Networking 2009
Detecting unnecessary iBGP-caused withdraws
16
RouteView Collector
R2R1
AS2
AS1
AS3
AS4
> P : 2 P : 3 4> P : 2> P : 2
Withdraw detected
P : 2> P : 3 4 P : 2
> P : 3 4
P : 1 3 4
Timer expiredNo withdraw from R2
MATCH
V. Van den Schrieck - Networking 2009
Quantification of iBGP-caused withdraws on RouteViews sessions
17
0
5000
10000
15000
20000
25000
30000
35000
40000
01-10-2008
02-10-2008
03-10-2008
04-10-2008
05-10-2008
06-10-2008
07-10-2008
08-10-2008
09-10-2008
10-10-2008
11-10-2008
12-10-2008
13-10-2008
14-10-2008
Num
ber
of w
ithdra
ws
Days
V. Van den Schrieck - Networking 2009
Agenda
• Introduction
• Presentation and evaluation of iBGP-caused withdraws
• Preventing iBGP-caused withdraws
✓ Advertising more than one path in iBGP (IETF)
✓ Our proposal : Advertising the availability of alternate paths in iBGP
18
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
P : 2 1P : 4 3 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1 P : 4 3 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1 P : 4 3 1
> P : 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1 P : 4 3 1
W(P)
> P : 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1 P : 4 3 1
P : 5 4 3 1
P : 2 1 > P : 4 3 1
W(P)
> P : 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
19
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1> P : 2 1 P : 4 3 1
P : 5 4 3 1
P : 2 1 > P : 4 3 1
W(P)
> P : 5 4 3 1
P : 2 1 > P : 4 3 1
> P : 1
V. Van den Schrieck - Networking 2009
Advertising multiple paths in iBGP
• Very promising solution, but :
✓ Need to modify the BGP protocol to support advertisement of multiple paths for a prefix
✓ All the routers of an AS need to be upgraded accordingly
20
V. Van den Schrieck - Networking 2009
Agenda
• Introduction
• Presentation and evaluation of iBGP-caused withdraws
• Preventing iBGP-caused withdraws
✓ Advertising more than one path in iBGP (IETF)
✓ Our proposal : Advertising the availability of alternate paths in iBGP
21
V. Van den Schrieck - Networking 2009
How to prevent iBGP-caused withdraws? (2)
• Instead of advertising alternate paths, advertise the availability of alternate paths
• BGP Community attribute used to tag this information to the path : DIVERSITY_AVAILABLE
• Lighter solution than the previous one, can be incrementally deployed
✓ No modification to BGP protocol
✓ DIVERSITY_AVAILABLE BGP community is simply not considered by legacy routers
22
V. Van den Schrieck - Networking 2009
Advertising the availability of alternate paths
• Principle :
✓ A router knowing an alternate path
- Tags the community DIVERSITY_AVAILABLE to the primary path
- Then, it re-advertises the primary path to all its iBGP peers
23
V. Van den Schrieck - Networking 2009 24
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
Advertising the availability of alternate paths
V. Van den Schrieck - Networking 2009 24
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1
P : 2 1 - DIV_AV
Advertising the availability of alternate paths
V. Van den Schrieck - Networking 2009 24
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1 P : 5 2 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
P : 2 1 - DIV_AV
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
V. Van den Schrieck - Networking 2009
Advertising the availability of alternate paths
25
• When the primary path fails :
• Routers without an alternate path check the community
✓ If present : Wait for the alternate path before sending withdraws on eBGP
✓ Otherwise : send the withdraw on eBGP sessions immediately
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
W(P)
> P : 1
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
No eBGP WithdrawWait alternate path
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
W(P)No eBGP WithdrawWait alternate path
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
P : 2 1 > P : 4 3 1
No eBGP WithdrawWait alternate path
> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
P : 2 1 > P : 4 3 1
P : 4 3 1
No eBGP WithdrawWait alternate path
> P : 3 1 P : 5 2 1
W(P)
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
P : 2 1 > P : 4 3 1
P : 4 3 1
P : 2 1 - DIV_AV> P : 4 3 1
No eBGP WithdrawWait alternate path
> P : 3 1 P : 5 2 1
W(P)> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
P : 2 1 > P : 4 3 1
P : 2 1 - DIV_AV> P : 4 3 1
P : 5 4 3 1
> P : 3 1 P : 5 2 1> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009 2619
12
AS1
AS3
AS4
AS2AS6
AS5R1
R2
eBGP sessioniBGP session
> P : local
> P : 3 1
> P : 1
> P : 1
> P : 2 1 P : 4 3 1
> P : 5 2 1
> P : 2 1 - DIV_AV
Advertising the availability of alternate paths
> P : 1
> P : 2 1 - DIV_AV
P : 2 1 > P : 4 3 1
P : 2 1 - DIV_AV> P : 4 3 1
P : 5 4 3 1
> P : 5 4 3 1
> P : 3 1 P : 5 2 1> P : 3 1 P : 5 2 1
V. Van den Schrieck - Networking 2009
Policy-equivalent paths
• In practice : due to policies, alternate paths can still trigger eBGP withdraws
✓ Use two communities instead of one
27
V. Van den Schrieck - Networking 2009
Conclusion
• We highlighted the contribution of iBGP-caused withdraws to BGP churn
• Two solutions to prevent this unnecessary withdraw propagation :
✓ Add-Paths (IETF)
✓ Our proposal : Diversity communities
• Work in progress : Evaluate the reduction of churn resulting from using our solution
✓ Simulations on generated Internet topologies
28
V. Van den Schrieck - Networking 2009
Questions?
• More information on : http://inl.info.ucl.ac.be
29