On 10 November 2016 at 05:59, Mark Tinka <mark.tinka@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.