[192607] in North American Network Operators' Group
Re: OSPF vs ISIS - Which do you prefer & why?
daemon@ATHENA.MIT.EDU (Mark Tinka)
Thu Nov 10 01:12:12 2016
X-Original-To: nanog@nanog.org
To: RT Parrish <routetarget@gmail.com>, Michael Bullut <main@kipsang.com>
From: Mark Tinka <mark.tinka@seacom.mu>
Date: Thu, 10 Nov 2016 08:12:05 +0200
In-Reply-To: <CAO-ok8Rfq5WDHzLFGfgvmrhE9A14Ztw0waaxhM8Coo_fj=buvg@mail.gmail.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces@nanog.org
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 occasion=
ally
> 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 firs=
t.
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 for=
m
> 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 desir=
ed
> 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.
