[162974] in North American Network Operators' Group
Re: ISIS and OSPF together
daemon@ATHENA.MIT.EDU (Victor Kuarsingh)
Sun May 12 15:57:55 2013
Date: Sun, 12 May 2013 15:57:34 -0400
From: Victor Kuarsingh <victor@jvknet.com>
To: Glen Kent <glen.kent@gmail.com>
In-Reply-To: <CAPLq3UM3wrUQ8cwY9QcKihc7ijL+jSfUgPPFeWxb6SguzSaPgA@mail.gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Glen,
Yes, if you are referring to RFC5838 like functionality in OSPFv3 (AF
support) that is correct. I personally don't have experience with that mod=
e
of operation (as the networks I had experience with went dual stack a while
back).
I guess someone looking to dual stack now may want to consider that option.
I am personally biased towards IS-IS when looking to do both, but to each
their own.
To further my early points (not saying it's a good option, but adding some
context). The rationale for keeping OSPFv2 was due to legacy tools and
operational procedures. Adding a second IGP (years ago) for IPv6 was
considered (to some) a way of not specifically impacting the "bread and
butter" IPv4 service while turning up IPv6.
I guess all of that reasoning has likely changed for new IPv6 turn-ups as
there is much more operational experience with running multiple AFs now.
I should have highlighted the context before =AD sorry.
Regards,
Victor K
From: Glen Kent <glen.kent@gmail.com>
Date: Mon, 13 May 2013 00:13:38 +0530
To: Victor Kuarsingh <victor@jvknet.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Subject: Re: ISIS and OSPF together
Victor,
Folks could, at least theoretically, use ISIS or OSPF multi instance/multi
topology extensions to support IPv4 and IPv6 topologies. This way they woul=
d
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@jvknet.com> wrote=
:
> Glen,
>=20
> 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).
>=20
> In those cases, the overlap period may not be very short (years vs.
> weeks/months).
>=20
> 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 a=
m
> 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.
>=20
> 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)
>=20
> Regards,
>=20
> Victor K
>=20
>=20
>=20
> On 2013-05-12 4:41 AM, "Glen Kent" <glen.kent@gmail.com> wrote:
>=20
>> >Hi,
>> >
>> >I would like to understand the scenarios wherein the service
>> >provider/network admin might run both ISIS and OSPF together inside the=
ir
>> >network. Is this something that really happens out there?
>> >
>> >One scenario that i can think of when somebody might run the 2 protocol=
s
>> >ISIS and OSPF together for a brief period is when the admin is migratin=
g
>> >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 anoth=
er
>> >AS (due to mergers and acquisitions) and the two ASes happen to run ISI=
S
>> >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 on=
ly
>> >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
>=20
>=20
