Subject: Re: OSPFv3 Applications Support

From: "Naidu, Venkata" <[email-masked]>
Date: Wed, 12 Mar 2003 15:47:46 -0500

[1]
-> run OSPFv3 separately from
-> OSPFv2 wherever both ipv4 and ipv6 were needed.
[2]
-> In one implementation, OSPFv3 and OSPFv2 share more than
-> 80 percent of the code. The less than 20 % comes from the
-> differences between the 2 protocols,

  Don't you think above [1] & [2] statements are contradictory.
  If 80% of the code is same, then why should any
  customer prefer to run different instances when the
  code is almost same.

  In other words, if integrated-ISIS can handle both ISO
  and IPv4 address, will you prefer to run two ISIS instances
  (one for ISO and one IPv4) when a single ISIS instance can
  handle both addresses independently.

  I would like to know the "technical" & "operational"
  advantages of running two different instances of the
  (almost) same protocol(s).

Venkata.

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From: Dave Katz <[email-masked]>
Date: Wed, 12 Mar 2003 13:35:25 -0800

Code commonality is entirely orthogonal to the issue of whether you
run integrated or SIN.  As an extreme example, cisco's ISIS and NLSP
share about 98% of the code, but they are most decidedly run
independently.

Customer acceptance and compatibility is a biggie; until everybody has
a *stable* OSPFv3, nobody in their right mind will bet their IPv4
network on it (and can't in any case if the code's not there.)

SIN is usually going to be more flexible, as you can have totally
independent configurations and topologies.

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From: Quaizar Vohra <[email-masked]>
Date: Wed, 12 Mar 2003 14:13:19 -0800

Admittedly the protocols aren't exactly the same. My last
mail did highlight the main differences. One being the
change in LSA formats. And that is obviously the
reason for running 2 instances of a similar protocol.
But that doesn't still mean that the protocols are different.
I was trying to argue against complete redesign of how IPv4
prefixes are carried in OSPFv3. That is a much farther
stretch than carrying OSPFv2 LSAs as it is in OSPFv3 with
just new LSA types. The former will also require
code to be written for translation of OSPFv2 LSAS to
OSPFv3 LSAs. Isn't addtional code complexity enough
of a technical reason.

As things stand, i.e. seperate protocols for IPv4 and
IPv6, work well enough currently. What's your techical
reason for modiyfing OSPFv3 to carry IPv4 prefixes. I
think my objections in the last mail were technical enough.
I don't see any merits in modifying a protocol (a complete
redesign, let alone just a simple change) just to be able to
run one instance of the protocol.

Your ISIS argument holds if that was the case with OSPF
from the start. That is not the case. People already
have deployed OSPFv2. They will have to run OSPFv2
for a long time no matter what.

I fail to see the configuration complexity argument as
there are other ways of solving that problem. I also
fail to see the control traffic overhead or more
burden on the control plane argument.

Quaizar

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From: Erblichs <[email-masked]>
Date: Sun, 16 Mar 2003 17:25:40 -0800

I think people are missing the big picture.

The question is not how much code is the same, but
how much should it differ in the future.

I see that IPv4 / OSPFv2 is a somewhat stable version
with a certain number of legacy routers that will never
have new functionality code added to their "firmware".

With this is mid it will be very difficult not to
support some level of ships in the night (SIN) approach.

Mitchell Erblich
Sr Software Engineer
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