Network operators using IS-IS on Cisco should be aware of a problem which can result in their routers reloading unexpectedly when a corrupt IS-IS packet is received. Cisco has fixed the problem in various 12.0 software trains. The problem can cascade through a single provider's network. Because IS-IS is an IGP protocol, it does not propagate between providers. This has already affected a provider. I haven't found out what is originating the bad IS-IS packet, i.e. is this an inter-vender operability issue?