BGP route propagation between neighboring domains Renata Teixeira Laboratoire LIP6 – CNRS University Pierre et Marie Curie – Paris 6 with Steve Uhlig (Delft University of Technology) Christophe Diot (Thomson)

1 Propagation of routing changes LIP6 DT AS 1 AS 3 AS 2 Lip6 down eBGP iBGP Which routing changes propagate between domains? How long does it take? Which factors determine propagation delay?

2 Why understand route propagation?  Improve protocol convergence – Which components have greater impact in convergence time?  Root-cause analysis – When did a routing change happen at the origin network?

3 Previous studies  Detailed data from one AS – Full routing information from one network BGP, intra-domain routing, router configs – No propagation between ASes  Few vantage points at multiple ASes – Publicly-available BGP feeds RIPE, RouteViews – Limited visibility and knowledge of networks

4 Our approach  Full routing data from two neighbor ASes – Abilene: US research network – GEANT: European research network  Correlate routing changes – From Abilene to GEANT and vice-versa

5 Abilene and GEANT Abilene GEANT Internet NY WA AM FR

6 Challenges  Monitoring infrastructure and data semantics depends on the network – Pre-process data  A single event may cause multiple messages – Group related routing messages in time (70 secs)  Timing depends on network and router configs – Examine router configurations and BGP

7 Measurement infrastructure Abilene GEANT BGP mon ATL BGP mon NY WA AM FR Abilene: - Monitors act as clients of operational router - Receive all BGP changes GEANT: - Monitor is a BGP peer - Only receive routes learned externally

8 Measuring route propagation Abilene GEANT ATL BGP mon Univ t1, ATL withdrawal Univ t2, AM withdrawal Univ NY WA AM FR Propagation time = t2 – t1 t3, FR withdrawal Univ

9 Components of route propagation Abilene GEANT ATL BGP mon Univ NY WA AM FR 1. ATL to NY and WA: iBGP out delay and propagation delay load to transfer all routes 2. NY to AM and WA to FR eBGP out delay Route-flap damping (depends on the prefix) 3. AM or FR to BGP mon iBGP out delay and propagation delay load to transfer all routes 1 2 3

10 Configuration of Abilene and GEANT  Abilene: – iBGP/eBGP out delay=0 – No route-flap damping – Low load: Few prefixes and BGP sessions  GEANT: – iBGP out delay=0 – eBGP out delay=10s and 30s – Route-flap damping – High load: Full BGP tables (180K prefixes)

11 Propagation of BGP updates From Abilene to GEANT From GEANT to Abilene propagation time fraction of correlated routing changes ~36% of route changes from Abilene to GEANT propagate immediately Other route changes depend on route-flap damping

12 Propagation of BGP updates From Abilene to GEANT From GEANT to Abilene propagation time fraction of correlated routing changes out delay from GEANT to Abilene depends on the peering point Most routing changes (over 60%) depend on the load to transfer multiple routes

13 Summary  Methodology to correlate BGP changes from neighbor ASes  Components of route propagation – Router configuration Out delay, route-flap damping – Network connectivity Prefixes per session and number of sessions