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 <[email protected]> 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" <[email protected]> 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 > > >
