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==Count to infinity problem==
The [[Bellman–Ford algorithm]] does not prevent [[routing loop]]s from happening and suffers from the '''count to infinity problem'''. The core of the count- to- infinity problem is that if A tells B that it has a path somewhere, there is no way for B to know if the path has B as a part of it. To see the problem, imagine a subnet connected like A–B–C–D–E–F, and let the metric between the routers be "number of jumps". Now suppose that A is taken offline. In the vector-update-process B notices that the route to A, which was distance 1, is down – B does not receive the vector update from A. The problem is, B also gets an update from C, and C is still not aware of the fact that A is down – so it tells B that A is only two jumps from C (C to B to A). Since B doesn't know that the path from C to A is through itself (B), it updates its table with the new value "B to A = 2 + 1". Later on, B forwards the update to C and due to the fact that A is reachable through B (From C's point of view), C decides to update its table to "C to A = 3 + 1". This slowly propagates through the network until it becomes infinity (in which case the algorithm corrects itself, due to the relaxation property of Bellman-Ford).
===Workarounds and solutions===
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==Further reading==
* [http://docwiki.cisco.com/wiki/Routing_Basics#Link-State_Versus_Distance_Vector Section "Link-State Versus Distance Vector"] {{Webarchive|url=https://web.archive.org/web/20101214043441/http://docwiki.cisco.com/wiki/Routing_Basics#Link-State_Versus_Distance_Vector |date=2010-12-14 }} in the Chapter "Routing Basics" in the [[Cisco Systems|Cisco]] "Internetworking Technology Handbook"
* [httphttps://authorscsc-knu.phptrgithub.comio/tanenbaumcn4sys-prog/books/Andrew%20S.%20Tanenbaum%20-%20Computer%20Networks.pdf Section 5.2 "Routing Algorithms"] in Chapter "5 THE NETWORK LAYER" from "Computer Networks" 4th.5th Edition by Andrew S. Tanenbaum and David J. Wetherall
