On 10 November 2016 at 05:59, Mark Tinka <mark.ti...@seacom.mu> wrote: > > > On 9/Nov/16 19:12, Michael Bullut wrote: > >> Greetings Team, >> >> While I haven't worked with IS-IS before but the only disadvantage I've >> encountered with OSPF is that it is resource intensive on the router it is >> running on which is why only one instance runs on any PE & P device on an >> ISP network. OSPF is pretty good in handling the core network routing while >> BGP & EGP handle the last-mile routing between PE & CE devices. BGP & EGP >> can run on top of OSPF. I came across this *article* >> <https://routingfreak.wordpress.com/2011/03/05/why-providers-still-prefer-is-is-over-ospf-when-designing-large-flat-topologies/> >> when >> scrolling the web a while back and I still want to find out if am the only >> one who thinks its a matter of choice between the two. Although there isn't >> distinct 1:1 argument, it's good we discuss it here and figure out why one >> prefer one over the other *(consider a huge flat network)**.* What say you >> ladies and gentlemen? > > I've given a talk about this a couple of times since 2008. But our > reasons are to choosing IS-IS are:
I don't think there is much of a debate to be had any more, the gap between them is so small now (OSPFv3 and ISIS that is, no one would deploy OSPFv2 now in greenfield right?): > * No requirement to home everything back to Area 0 (Virtual Links are > evil). This is a good point I think. > * Integrated IPv4/IPv6 protocol support in a single IGP implementation. This is in OSPv3. > * Single level (L2) deployment at scale. Single area 0 deployment at scale? Bit of a moot point unless you compare a specific device model and specific code version in two identical deployments, its not much to do with the protocol but the vendor implementation and the brute force. > * Scalable TLV structure vs. Options structure for OSPFv2. OSPFv3 > employs a TLV structure, however. OSPv3 has this. > * Inherent scaling features, e.g., iSPF, PRC, e.t.c. Some of these may > not be available on all vendor implementations. OSPF has these too. > Ultimately, router CPU's are way faster now, and I could see a case for > running a single-area OSPFv2. So I'd likely not be religious about > forcing you down the IS-IS path. Yeah this ^ I don't think there is a stronge case for either protocol. Somenoe mentioned the AOL NANOG talk about migrating from OSPF to ISIS. There was a NANOG talk recently-ish about someone migrating from OSPF to BGP. There wasn't even a need for an IGP, BGP scalled better for them (in the DC). BGP these days supports PIC and BFD etc, how much longer to IGPs have? :) James.