[192604] in North American Network Operators' Group
Re: OSPF vs ISIS - Which do you prefer & why?
daemon@ATHENA.MIT.EDU (Mark Tinka)
Thu Nov 10 00:59:20 2016
X-Original-To: nanog@nanog.org
To: Michael Bullut <main@kipsang.com>, nanog@nanog.org
From: Mark Tinka <mark.tinka@seacom.mu>
Date: Thu, 10 Nov 2016 07:59:12 +0200
In-Reply-To: <CAGy+NY0R+9fBSRH5RKNc7mp4aF4B3K0c+CTwVuSakHsfF8r0ng@mail.gmail.com>
Errors-To: nanog-bounces@nanog.org
On 9/Nov/16 19:12, Michael Bullut wrote:
> Greetings Team,
>
> =E2=80=8BWhile I haven't worked with IS-IS before but the only disadvan=
tage 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 w=
hile
> BGP & EGP handle the last-mile routing between PE & CE devices. BGP & E=
GP
> can run on top of OSPF. I came across this *article*
> <https://routingfreak.wordpress.com/2011/03/05/why-providers-still-pref=
er-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 o=
nly
> one who thinks its a matter of choice between the two. Although there i=
sn'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:
=20
http://www.apricot.net/apricot2009/images/lecture_files/isis_deployment.p=
df
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.
