Interior Gateway Protocols

IGPs are historically considered to be slow in detecting and recovering from failures in the network. However, this no longer has to be the case. Sure, the default timers for Open Shortest Path First (OSPF) can cause a router to take up to 40 seconds to declare a link down, but did you know that for OSPF and Intermediate System to Intermediate System (IS-IS) you can reduce the dead interval to as low as one second?

[edit]
lab@r1# set protocols ospf area 0 interface so-0/1/0 dead-interval ?
Possible completions:
  <dead-interval>      Dead interval (seconds) (1..65535)

This capability has the potential to completely change the way networks are designed in relation to protocol failover strategies. Where previously an IGP timer might have been a hindrance, requiring reliance on other mechanisms for fast failure detection and failover, the fast timers for these IGP protocols mean they can now arguably provide high availability capabilities all on their own.

Warning

Just because you can configure extremely low IGP timers doesn’t mean you should. While the low timer settings for IGPs on JUNOS devices provide the option to use these protocols to maintain high availability networks, in practice routing protocols are no longer used as a primary means of quick failure detection and recovery. This is true to such an extent that these days it is not recommended to use extremely low timers at all. With the introduction of newer mechanisms that are purpose-built to provide extremely ...

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