Re: 'Faulty Router'
One faulty router brings the network down?
If it starts announcing gibberish instead of what it is supposed to announce as routing updates - why not.
There is bugger all protection at the routing protocol level for most internal gateway protocols. OSPF has none by design (no, do not talk to me about the admin weight hack in Cisco IOS the person who invented that should be shot), ISIS is not much better, iBGP is usually unfiltered as well and let's not even talk about various protos that used to be popular with with BT CTO like PBB and PBB-TE.
The solution in this case is to have good "view"/"analysis" of the routing protocol state and KILL the router from the wall switch right away to localize the failure. I am not going to comment on BT and either one of these.
Biting the hand that feeds IT
