This generally supports my own view that it depends on the topology and the real or potential scale/scope. In my experience, IS-IS is just all around better in a flat, highly interconnected environment such as an ISP or other broadly scaled network. If you have a very (almost exclusively) heirarchical structure and pretty good control over IP addressing and can use summarization effectively, then OSPF can make your core networking much simpler. On a small network that doesn't look to grow at leaps and bounds, I'd favor OSPF. On a large, complex network or a network that has the potential to grow without any sort of predefined structure (ie, more demand based), then IS-IS is probably your win. Note that this doesn't factor in multiple IS-IS levels, something I don't have a great deal of experience with. Mostly, networks I've been associated with just run one great big, gigantic level 0, though they did also experiment with other configurations.
-Wayne On Thu, Nov 10, 2016 at 07:59:12AM +0200, Mark Tinka 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: > > * No requirement to home everything back to Area 0 (Virtual Links are > evil). > > * Integrated IPv4/IPv6 protocol support in a single IGP implementation. > > * Single level (L2) deployment at scale. > > * Scalable TLV structure vs. Options structure for OSPFv2. OSPFv3 > employs a TLV structure, however. > > * Inherent scaling features, e.g., iSPF, PRC, e.t.c. Some of these may > not be available on all vendor implementations. > > If you're interested in reviewing the talk I gave on this, a lot more > details is in there at: > > > http://www.apricot.net/apricot2009/images/lecture_files/isis_deployment.pdf > > 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. > > Mark. > --- Wayne Bouchard [email protected] Network Dude http://www.typo.org/~web/
