Re: [OSPF] draft-chen-ospf-transition-to-ospfv3-00.txt

Hi Karsten,
We wil add Ran's suggested text to the next revision.
Thanks,
Acee

From: Karsten Thomann <karsten_thomann@linfre.de<mailto:karsten_thomann@linfre.de>>
Date: Saturday, February 15, 2014 4:22 AM
To: OSPF - OSPF WG List <ospf@ietf.org<mailto:ospf@ietf.org>>
Subject: Re: [OSPF] draft-chen-ospf-transition-to-ospfv3-00.txt

Am Montag, 10. Februar 2014, 14:33:05 schrieb RJ Atkinson:

> Earlier, Karsten Thomann wrote, in part:

> > I don't know if i have missed that part, but what would happen if OSPFv3

> > is running over IPv4 and there are two (or more) IPv6 Islands already

> > deployed within the network, should there be any LSA flooding checks,

> > like do not flood LSA with IPv6 networks over IPv4 only links, or should

> > the route

> > calculation/installation of the information simply fail

> > as there is no valid path?

>

> The OSPF deployments I am familiar with did not "auto deploy"

> or "self deploy". Instead, all of the OSPF deployments that I am

> familiar with had engineers making deliberate decisions about how

> to configure the OSPF deployment, and also how to configure the

> OSPF routers in that deployment.

I know that such deployments are normally well planned, but as there is already a draft about ospfv3 autoconfig, even if it is not designed to be used in company networks.

> One deployment option, already deployed in some places, is to run

> "ships in the night". In this model, the IPv4 topology exclusively

> uses OSPFv2 over IPv4 and the IPv6 topology exclusively uses OSPFv3

> over IPv6. For some sites, that is a good option. A number of my

> clients are very interested in this new I-D because it optimises

> their IPv6 transition strategy.

>

> For some sites, IPv6 transition is simplified, optimised, and also

> cost-reduced by using OSPFv3 over IPv4 initially, and carrying both

> IPv4 prefixes and IPv6 prefixes inside that one OSPFv3 deployment

> (i.e. using the Address Family extension to keep the prefixes clearly

> differentiated within a single OSPFv3 deployment). This can lower

> operational costs because one can get by with managing only OSPFv3,

> rather than having to manage both OSPFv2 and OSPFv3.

>

> If one's "IPv6 islands" (to use your term) are really dual-stack

> (aside: having dual-stack rather than IPv6-only would be expected

> and normal if another part of one's OSPF deployment is using

> OSPF over IPv4), then EITHER the whole deployment should be configured

> to run over IPv4 XOR the whole deployment should be configured

> to run over IPv6.

>

> Having different "IPv4 islands" and "IPv6 islands" is an explicit choice

> of a configuration engineer or design engineer. That probably is not

> the optimal deployment choice for an engineer to make. It definitely

> is NOT a choice that I would make or that I would recommend to my clients.

I would not do it either, but I have already seen some strange ospf designs..., and as mentioned it is a case which can happen with ospf autoconfiguration, but we don't need to discuss it further as it is for homenetworks

> From the descriptions and definitions in the draft, it would not be

> "normal" or "expected" to mix IPv6 transport with IPv4 transport

> within a single OSPFv3 deployment.

>

> > Is there any explicit preference over which version the adjacency

> > is build if v4 and v6 is available in that specific part of the network?

>

> The choice of preferred OSPF transport really is something that the

> configuration engineer ought to configure. As the details of configuring

> any IP router are outside the scope of the IETF, I am not sure that

> this I-D properly can or should say very more than it already says.

>

> Perhaps the I-D could add clarifying text along these lines

> somewhere in Section 2:

>

> "Implementers of OSPFv3 over IPv4 SHOULD add a configuration

> knob to let the router administrator select whether a given

> OSPFv3-enabled interface should use OSPFv3 over IPv4 or

> OSPFv3 over IPv6. Except when an OSPFv3 deployment is being

> transitioned from using IPv4 transmission to using IPv6

> transmission, it is RECOMMENDED that all routers within an

> OSPFv3 deployment use the same IP version for OSPFv3 packet

> transmission."

>

> > What should happen when an IPv4 Link gets v6 added, graceful reestablish

> > the adjacency over IPv6, or wait until forced protocol switch?

>

> See my answer just above.

>

> I would expect that any router that implements this I-D also would implement

> a configuration knob to indicate whether IPv4 transmission or IPv6

> transmission is preferred. Over time, a configuration engineer might

> change this (e.g. manually change from IPv4 transmission to IPv6

> transmission AFTER an entire IPv4 network has been

> deployed-with/converted-to dual-stack IPv4 and IPv6).

>

> Yours,

>

> Ran Atkinson

Thanks for the detailed anwsers, I'm satisfied with the addition.

Kind regards,

Karsten

>

>

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