Hot-potato routing

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In Internet routing between autonomous systems which are interconnected in multiple locations, hot-potato routing is the practice of passing traffic off to another autonomous system as quickly as possible, thus using their network for wide-area transit. Cold-potato routing is the opposite, where the originating autonomous system internally forwards the packet until it is as near to the destination as possible. [1] [2] [3]

Contents

Behaviors

Hot-potato routing (or "closest exit routing") [2] is the normal behavior generally employed by most ISPs. [1] Like a hot potato in the hand, [2] the source of the packet tries to hand it off as quickly as possible in order to minimize the burden on its network. [1]

Cold-potato routing (or "best exit routing") [2] on the other hand, requires more work from the source network, but keeps traffic under its control for longer, allowing it to offer a higher end-to-end quality of service to its users. [1] It is prone to misconfiguration as well as poor coordination between two networks, which can result in unnecessarily circuitous paths. [1] NSFNET used cold-potato routing in the 90s. [2]

When a transit network with a hot-potato policy peers with a transit network employing cold-potato routing, traffic ratios between the two networks tend to be symmetric. [2]

Implementation

Routing behavior can be influenced using two BGP "knobs": multi-exit discriminator (MED) and local preference. [1] In hot-potato routing, the MED attached to incoming EBGP-learned routes is discarded, [2] and the IGP cost is used instead. [3] In cold-potato routing, MED [2] or BGP communities are used to signal the cost of the route, which influences IBGP local preference. [3]

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References

  1. 1 2 3 4 5 6 Subramanian, Lakshminarayanan; Padmanabhan, Venkata N.; Katz, Randy H. (2002-06-10). Geographic Properties of Internet Routing (PDF). USENIX 2002 Annual Technical Conference.
  2. 1 2 3 4 5 6 7 8 McPherson, D.; Patel, K. (January 2006). "MEDs and Potatoes". Experience with the BGP-4 Protocol. IETF. p. 5. sec. 7.1.1. doi: 10.17487/RFC4277 . RFC 4277 . Retrieved 2023-12-11.
  3. 1 2 3 Decraene, B.; Francois, P.; Pelsser, C.; Ahmad, Z.; Armengol, A.J. Elizondo; Takeda, T. (April 2011). "Routing Decisions". Requirements for the Graceful Shutdown of BGP Sessions. IETF. p. 18. sec. A.3. doi: 10.17487/RFC6198 . RFC 6198 . Retrieved 2023-12-12.
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