ISIS and OSPF together

Glen Kent glen.kent at gmail.com
Sun May 12 18:43:38 UTC 2013


Victor,

Folks could, at least theoretically, use ISIS or OSPF multi instance/multi
topology extensions to support IPv4 and IPv6 topologies. This way they
would only need to run a single protocol and thereby requiring expertise in
handling only one protocol.

With whatever i remember, OSPFv3 can be used to support IPv4 as well - so
folks could also use OSPFv3 when they want to support both IPv4 and IPv6.

Glen

On Sun, May 12, 2013 at 6:17 PM, Victor Kuarsingh <victor at jvknet.com> wrote:

> Glen,
>
> One transition scenario you noted below is often a use case.  I have seen
> networks move from OSPF to IS-IS (more cases then the reverse).
>
> In those cases, the overlap period may not be very short (years vs.
> weeks/months).
>
> I have also seen some use one protocol (which I think was mentioned in
> another response) used for IPv4 and another used for IPv6.  The cases I am
> familiar, tended to be IPv6 with IS-IS and IPv4 with OSPFv2.
> I guess the reasoning here was that if you are running dual stack, with
> OSPF you will need to run two protocols anyway, so running OSPFv2(IPv3)
> and OSPFv3(IPv6) may not be that different then running OSPFv2(IPv4) with
> IS-IS(IPv6).  This dual stack option has run longer or is semi-permanent
> at times.
>
> A sub-case to the above may also be that one (operator) may want to
> leverage some of capabilities of IS-IS and may not be willing to get off
> OSPF for some reason.  The Multi-topology option in IS-IS may be quite
> useful if you have some functions which are non-congruent in your network
> and you want to maintain topology variations (multicast being one, or
> in-band management which I believe was alluded to in your OOB use case)
>
> Regards,
>
> Victor K
>
>
>
> On 2013-05-12 4:41 AM, "Glen Kent" <glen.kent at gmail.com> wrote:
>
> >Hi,
> >
> >I would like to understand the scenarios wherein the service
> >provider/network admin might run both ISIS and OSPF together inside their
> >network. Is this something that really happens out there?
> >
> >One scenario that i can think of when somebody might run the 2 protocols
> >ISIS and OSPF together for a brief period is when the admin is migrating
> >from one IGP to the other. This, i understand never happens in steady
> >state. The only time this can happen is if an AS gets merged into another
> >AS (due to mergers and acquisitions) and the two ASes happen to run ISIS
> >and OSPF respectively. In such instances, there is a brief period when two
> >protocols might run together before one gets turned off and there is only
> >one left.
> >
> >The other instance would be when say OSPF is used to manage the OOB
> >network
> >and the ISIS is used for network reachability.
> >
> >Is there any other scenario?
> >
> >Glen
>
>
>


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