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Providing scalable NH-diverse iBGP route redistribution to achieve sub-second switch-over time
Citation key PUTQS-PSNIRRASST-10
Author Pelsser, Cristel and Uhlig, Steve and Takeda, Tomonori and Quoitin, Bruno and Shiomoto, Kohei
Pages 2492–2505
Year 2010
ISSN 1389-1286
DOI http://dx.doi.org/10.1016/j.comnet.2010.04.007
Journal Computer Networks
Volume 54
Number 14
Month October
Publisher Elsevier
Abstract The role of BGP inside an AS is to disseminate the routes learned from external peers to all routers of the AS. A straightforward, but not scalable, solution, is to resort to a full-mesh of iBGP sessions between the routers of the domain. Achieving scalability in the number of iBGP sessions is possible by using Route Reflectors (RR). Relying on a sparse iBGP graph using RRs however has a negative impact on routers' ability to quickly switch to an alternate route in case of a failure. This stems from the fact that routers do not often know routes towards distinct next-hops, for any given prefix. In this paper, we propose a solution to build sparse iBGP topologies, where each BGP router learns two routes with distinct next-hops (NH) for each prefix. We qualify such iBGP topologies as NH-diverse. We propose to leverage the ``best-external'' option available on routers. By activating this option, and adding a limited number of iBGP sessions to the existing iBGP topology, we obtain NH-diverse iBGP topologies that scale, both in number of sessions and routing table sizes. We show that NH diversity enables to achieve sub-second switch-over time upon the failure of an ASBR or interdomain link. The scalability of our approach is confirmed by an evaluation on a research and a Service Provider network.
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