Re: [OSPF] OSPFv3 LSA Extendibility - draft-acee-ospfv3-lsa-extend-00.txt

Anton Smirnov <asmirnov@cisco.com> Fri, 28 June 2013 08:01 UTC

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Date: Fri, 28 Jun 2013 10:00:22 +0200
From: Anton Smirnov <asmirnov@cisco.com>
Organization: Cisco Systems
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To: Acee Lindem <acee.lindem@ericsson.com>
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Cc: "OSPF@ietf.org" <OSPF@ietf.org>
Subject: Re: [OSPF] OSPFv3 LSA Extendibility - draft-acee-ospfv3-lsa-extend-00.txt
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    Hi Acee,
    while I appreciate developer's simplicity of option 1 this approach 
is good only for greenfield deployment. For any existing sizable OSPFv3 
network its migration limitation may become an insurmountable obstacle.
    My preference is combination of options: start migration as option 2 
and when migration is completed lock on 1.
    Benefits are that migration is possible; LSDB is doubled only for 
period of migration; and once migration is completed there is no need to 
worry about dynamics of old-style router entering the domain.
    Downside is relative complexity of implementation but that's the 
price to pay for simplicity of OSPFv3. BTW, entering and exiting 
migration may be manual (via configuration), so this mixed approach may 
be simpler to implement than 'pure' option 3.
    Said all that, individual products targeting greenfield deployment 
scenario may skip implementation of migration. Say, homenet may require 
support of extended LSAs from day 1. That would mean that homenet 
products will not be deployable in existing old-style-LSA networks - but 
that probably is not the intent anyway.

Anton


On 06/27/2013 10:18 PM, Acee Lindem wrote:
> I don't think there is much disagreement that we need a direct way to
> extend the base OSPFv3 LSAs and I will be presenting this draft at IETF
> 87 in Berlin. Where there appears to be some amount of disagreement is
> in the backward compatibility mechanisms. There are basically 3 options
> (as well as subtle variants)
>
>
>          1. The approach in the draft, only allow adjacencies between
> routers supporting the extended encodings. Backward compatibility would
> have to be provided with separate instances and topology.
>
>         2. Both the current and extended versions of the LSAs are
> originated as long as there are routers not supporting the new extended
> encodings at the respective flooding scope. This was the approach taken
> in "Multi-toplogy routing in OSPFv3 (MT-OSPFV3)",
> draft-ietf-ospf-mt-ospfv3-04.txt. However, it has the undesirable
> property of roughly doubling the size of the LSDB.
>
>        3. Switch to the extended format only after all the routers at
> the flooding scope support it. Use OSPF demand circuit-like (RFC 1793)
> signaling to determine whether or not all routers in the flooding scope
> support the new format. The only potential problem with this approach is
> a dynamics when a router not supporting the extended format successively
> leaves and enters the routing domain.
>
> What is the WG preference? I'm still in favor of the approach in the
> draft (#1) given the simplicity and stability properties. What we'd lose
> in slowed deployment would be more than made up standardization and
> availability. Also, it would satisfy the homenet requirements we
> desperately need to satisfy.
>
> Thanks,
> Acee
>
>
>
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