{{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.<ref name="spk">{{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 }}</ref><ref name="rfc4277">{{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 }}</ref><ref name="rfc6198">{{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 }}</ref>
== Behaviors ==
Hot-potato routing (or "closest exit routing")<ref name="rfc4277"/> is the normal behavior generally employed by most ISPs.<ref name="spk"/> Like a hot potato in the hand,<ref name="rfc4277"/> the source of the packet tries to hand it off as quickly as possible in order to minimize the burden on its network.<ref name="spk"/> Hot-potato routing offers operational advantages such as reduced infrastructure costs, as traffic is handed off at the nearest exit point, avoiding the need for overseas POPs or dedicated submarine-cable capacity.<ref name="axclusive">{{cite web |title=Beyond Singapore’s Borders: How Axclusive’s International Network Delivers True End-to-End Connectivity |url=https://www.axclusive.com.sg/beyond-singapores-borders-how-axclusives-international-network-delivers-true-end-to-end-connectivity/ |website=Axclusive |access-date=2025-12-01 }}</ref>
Cold-potato routing (or "best exit routing")<ref name="rfc4277"/> 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.<ref name="spk"/> It is prone to misconfiguration as well as poor coordination between two networks, which can result in unnecessarily circuitous paths.<ref name="spk"/> NSFNET used cold-potato routing in the 90s.<ref name="rfc4277"/> Cold-potato routing enables providers to optimize paths based on real-time network conditions, troubleshoot issues without relying on third parties, and maintain more predictable delivery times. It also reduces the risk of packet loss due to congestion or oversubscription in external networks. <ref name="axclusive" />
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.<ref name="rfc4277"/>
== Implementation ==
Routing behavior can be influenced using two BGP "knobs": multi-exit discriminator (MED) and local preference.<ref name="spk"/> In hot-potato routing, the MED attached to incoming {{abbr|EBGP|Exterior Border Gateway Protocol}}-learned routes is discarded,<ref name="rfc4277"/> and the IGP cost is used instead.<ref name="rfc6198"/> In cold-potato routing, MED<ref name="rfc4277"/> or BGP communities are used to signal the cost of the route, which influences {{abbr|IBGP|Interior Border Gateway Protocol}} local preference.<ref name="rfc6198"/>
== References == {{reflist}}
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Category:Internet architecture *