Hi Ken, generally network convergence is composed of many components: 1) failure detection 2) propagation time of failure information 3) path recalculation timers All three of them can be the major component. As for 1): with static routing in place the time could even be infinity, if no link down event occurs. If "active testing" is involved, i.e. some keepalive mechanism, then the interval and dead timers determine the contribution to convergence. Today IGPs like OSPF or also spanning-tree (rstp) can be tuned to have hello/dead timers in the few second range (sometimes even subsecond). One should be careful though, as trying to convert a Toyota station waggon into a top fuel dragster by just fueling it with Nitro might break the thing ... ;-) In other words: there are limitations with respect to CPU load, memory and bandwidth, which need to be taken into account. As for 2): this depends on IGP or EGP update timers. Generally link-state protocolls are faster, BGP might be the slowest. There are also throtteling timers involved (to save the Toyota ;-) All the timers can usually be adjusted though to speed up the process. As for 3): There are also throtteling timers for path recalculation and the available CPU ressources are also of some importance. In addition the complexity of the recalculation is important. F.e. RIP will just insert an Update into the IP routing table whereas OSPF recalculates the topology in some cases. Final statement: the default timers are usually choosen conservatively, there is room for improovement in most cases. To lower convergence time in a complete network you need detailed knowledge on a protocoll and device feature level as well as on network specifics (like average CPU load in a router). Regards, Martin For further reading: Caveats in Testing Routing Protocol Convergence http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_8-4/testing_routing.html High Availability White Papers http://www.cisco.com/en/US/products/ps6550/prod_white_papers_list.html
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