OSPF vs ISIS - Which do you prefer & why?

Mark Tinka mark.tinka at seacom.mu
Thu Nov 10 14:33:27 UTC 2016

On 10/Nov/16 12:17, James Bensley wrote:

> 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?):

Most networks that I know are greenfielding an IGP will deploy both
OSPFv2 and OSPFv3. Worst case, just OSPFv2.

> This is in OSPv3.

Right, but if a network does not yet want to run IPv6 (2016, anyone),
then this becomes an issue as IPv6 NLRI is carried over the IPv6 transport.

This could also come down to implementation. I looked at this for the
first time back in Junos 9.0 (when it was still an IETF draft), and no
other vendor had it yet. It has since matured and I know both Juniper
and Cisco have decent code.

I can't speak for other vendors, particularly if you multi-vendor.

> 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.

Like I said to Randy, if I did deploy OSPF ever (quite unlikely), there
is enough CPU in today's router to, I think, run a single Area 0 for the
whole thing.

> OSPv3 has this.

Yep, as I did mention.

> OSPF has these too.

More of them in OSPFv3 than OSPFv2. But then again, vendor-specific
knobs can be had here for cheap.

> 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? :)

Sounds like you're talking about BGP-LS.

If you are, then BGP-LS still requires an IGP. It's just that the IGP
has a much more micro view of the network, while BGP-LS is tasked with
the macro side of things.


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