North American Network Operators Group

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Re: [nsp] IS-IS over IP?

  • From: Tony Li
  • Date: Wed Apr 05 05:51:14 2000

> > I wasn't in Adelaide, but in earlier meetings, I had the impression
> > that there were at least some implementations using IPv4 as a
> > workaround both to lower layer specific problems (e.g., AAL SNAP/MUX)
> > as well as the hard MTU size limit due to lack of fragmentation
> > capability at the data link layer.

The specific problem that certain people were trying to address was the need to run
a multiprotocol encapsulation on top of ATM, thereby (further) lowering the
efficiency of ATM while still running IS-IS in their networks.

> I don't believe there were any meetings of the ISIS WG in Adelaide.


> I'm not aware of any implementations of ISIS over IPv4, much less in production
> networks.

Neither am I.  However, there is at least one obvious person that you should
consult directly.

>  As for the MTU issue, most use maximum LSP size of 1492 bytes and
> even stop Hello padding after initialization.

There is no hard MTU issue.  The problem that the spec both created and tried to
address was that in running IS-IS over IP, it would be necessary to perform IP
fragmentation to deal with IS-IS packets that would otherwise fit in the CLNP MTU.