On 10/Nov/16 04:45, RT Parrish wrote:
1) Network Topology support - The differences between a single OSPF backbone area and a contiguous set of Level-2 adjacencies will occasionally be a deciding factor.
L2 IS-IS can be as chatty as single-area OSPF. That said, IS-IS has native tools to reduce that chatter (like PRC, and iSPF), but to be honest, I'm not sure it makes much of a difference given today's faster router CPU's.
2) Feature Support on a per vendor basis - Some vendors will roll new features out in one or the other protocols prior to the other. Segment Routing and some of its enhancements come to mind as being in ISIS first.
I've noticed that the delay between when IS-IS and/or OSPF pick up a feature the other already has is reasonable. By the time an OSPF has completed evaluating whether they need LFA, it would have been implemented in the IGP. I suppose back then, there was a much bigger between when features made it between both protocols, but things seem to be on par nowadays.
3) Layer 2 adjacencies - I think someone already mentioned that you form adjacencies at layer 2 which also means that with a single adj you can support multiple protocols (v4/v6). OSPF would require two different instances to support both. Maybe good, maybe not. Depends on your desired level of isolation between the two.
OSPFv3 can support the advertisement of IPv4 prefixes. But you'd still need an IPv6 link layer.
4) CPU performance is academic at this point - The SPF calculations in most networks would require next to no difference between the two protocols even if running both IPv4 and v6.
Agree.
End of the day, use the right tool/vendor/technology for the right job.
Agree. Mark.