Hot-potato routing
{{Short description|Conventions regarding Internet routing policy}}
{{for|the packet-switching technique|deflection routing}}
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.{{cite conference |url=http://sahara.cs.berkeley.edu/papers/SPK02.pdf |title=Geographic Properties of Internet Routing |first1=Lakshminarayanan |last1=Subramanian |first2=Venkata N. |last2=Padmanabhan |first3=Randy H. |last3=Katz |date=2002-06-10 |conference=USENIX 2002 Annual Technical Conference }}{{Cite IETF |title=Experience with the BGP-4 Protocol |rfc=4277 |section=7.1.1 |sectionname=MEDs and Potatoes |page=5 |last1=McPherson |first1=D. |last2=Patel |first2=K. |date=January 2006 |publisher=IETF |access-date=2023-12-11 |doi=10.17487/RFC4277 }}{{Cite IETF |title=Requirements for the Graceful Shutdown of BGP Sessions |rfc=6198 |appendix=A.3 |sectionname=Routing Decisions |page=18 |last1=Decraene |first1=B. |last2=Francois |first2=P. |last3=Pelsser |first3=C. |last4=Ahmad |first4=Z. |last5=Armengol |first5=A.J. Elizondo |last6=Takeda |first6=T. |date=April 2011 |publisher=IETF |access-date=2023-12-12 |doi=10.17487/RFC6198 }}
Behaviors
Hot-potato routing (or "closest exit routing") is the normal behavior generally employed by most ISPs. Like a hot potato in the hand, the source of the packet tries to hand it off as quickly as possible in order to minimize the burden on its network.
Cold-potato routing (or "best exit routing") 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. It is prone to misconfiguration as well as poor coordination between two networks, which can result in unnecessarily circuitous paths. NSFNET used cold-potato routing in the 90s.
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.
Implementation
Routing behavior can be influenced using two BGP "knobs": multi-exit discriminator (MED) and local preference. In hot-potato routing, the MED attached to incoming {{abbr|EBGP|Exterior Border Gateway Protocol}}-learned routes is discarded, and the IGP cost is used instead. In cold-potato routing, MED or BGP communities are used to signal the cost of the route, which influences {{abbr|IBGP|Interior Border Gateway Protocol}} local preference.