Why this work?

1. A Comparative Study of Architectural Impact on BGP Next-hop Diversity15th IEEE Global Symposium, March 2012 Jong Han Park1, Pei-chunCheng2, Shane Amante3, Dorian Kim4, Danny McPherson5, Lixia Zhang2 1AT&T Labs 2University of California, Los Angeles 3Level-3 Communications Inc. 4NTT Communications Inc. 5Verisign Inc.

2. Why this work? • Large ISPs have deployed i-BGP Route Reflections for scalability • Hierarchical Route Reflection has a common perception for reducing path diversity • Is the perception correct? • What factors have most impact on path diversity? • This measurement study aims to answer the above two questions

3. Next-Hop Diversity: Definitions POP1 • Next-hop POP: the city in which the next-hop router is located for a given destination prefix • Next-hop AS: the neighboring AS used to reach a given destination prefix NH Router1 ASX AS1 NH Router2 POP2 ASO Prefix p NH Router3 POP3 AS2 AS3

4. But not all existing paths visible

5. Data collection settings • Data collected from 2 large ISPs with different i-BGP architectures • ISPFM: full-mesh i-BGP backbone • ISPRR: hierarchical Route Reflection i-BGP backbone BGP data collection POPs ISPRR ISPFM Backbone sub-AS (full-mesh) sub-AS sub-AS sub-AS iBGP node type: iBGP router iBGP node type: 1st level reflector 2nd level reflector BGP confederation 3rd level reflector Peer Reflector to Client

6. Next-hop diversity of the 2 ISPs • Dataset: routing table snapshot on June 03, 2010 • ISPFM (ISPRR) has ~66% (50%) prefixes with next-hop POP diversity >=9 (7) • ISPFM (ISPRR) has ~10% (34%) of all prefixes with only one next-hop POP • ISPFM has higher overall next-hop diversity than ISPRR ISPFM ISPRR

7. Investigating the causes for the differences • Estimating available paths based on BGP dynamics [Oliveira’09] • Identify prefixes with at least one route flap (i.e., becoming completely unreachable from all routers and becoming reachable again) • Record all paths with associated BGP attribute values • Simulate BGP best path selection at the AS level • IN: available paths to reach a given prefix • OUT: amount of eliminated paths at each step of BGP best path selection **[Oliveira’09] Quantifying Path Exploration in the Internet by Oliveira et al, Transactions on Networking 2009

8. Examples of path elimination in simulation BGP best path selection 1. Highest Local preference PATH 1 AS1 2. Shortest AS_PATH length PATH 2 ASO Prefix p ASX 3. Lowest Origin PATH 3 4. Lowest MED PATH 4 5. Lowest IGP cost AS3 AS2 6. More … Path diversity loss due to Topology dependent factors -ASPathLen, Next-hop POP = 2 -Local_Pref, Next-hop POP = 3 Available Next-hop POP = 4 -Origin, Next-hop POP = 2 -MED, Next-hop POP = 1

9. Simulation results • Dataset: updates from all backbone routers during the 1st week of June 2010 • Both ISPs suffer a significant next-hop diversity reduction • The first 2 criteria reduces up to 42% • Only minor reduction (less than 2.9%) due to topology dependent factors

10. Well-engineered RR placement  min. diversity loss Tier-1 backbone RRs (continent) • Not all regions (or mega-POPs) are equal • Place more backbone RRs in the regions with higher prefix injection density • In case of ISPRR • For more than 50% of prefixes, RRs exist in the nearest POPs • The current RR placement is nearest for more than 85% of prefixes after eliminating paths using the top 4 BGP path selection criteria Available Tier-2 backbone RRs (regions or mega-POPs) B1 B3 B2 Tier-3 RRs (POPs) PEs Prefix p

11. Summary • Engineering efforts going on aiming to increase path diversity • Lack of quantitative study on existing path diversity and impacting factors • Our measurement/simulation results based on iBGP data from 2 large ISPs shed new insights: • Routing policies: main factor • Impact of different iBGP architectures insignificant • Can be further mitigated by well-engineered i-BGP topology

12. Questions?Thank you!