[Isis-wg] IS-IS Extensions for Traffic Engineering

[Henk Smit]

> A quick query regarding draft-ietf-isis-traffic-01.
> 
> In RFC 1195 we implement the Internal and External IP reachibilty
> TLVs in LSPs for ISIS routes (Internal), Non ISIS routes (External),
> for example (depending on route propagation policies). In addition
> the TLV allows the specification of metrics as being internal or
> external as well.
> 
> In the traffic engineering draft a single TLV (135) is used to hold
> IP reachibility information. However I do not see any bit field for
> specifying External/Internal for these routes. The internal/external
> bit for metrics I can live without

  Thank you.
 One of the reasons that we didn't put this in our draft is that
 the I/E metric bit is implemented wrongly in our IOS implementation.
 No customer ever really complained about it. So it seems the I/E
 metric bit is not used at all. At least not by our customers.

> but how do I map the old scheme
> to the daft proposal? Is there an unspecified Sub-TLV for doing
> this? Is the idea to go from old world Level1 Internal, Level2
> Internal/External routes to just flat Level1 and Level2 routes?

  Yes.
 Please note that in RFC1195, paragraph 3.10.2, 2c), there is a note,
 saying:

         NOTE: Internal routes (routes to destinations announced
         in the "IP Internal Reachability Information" field),
         and external routes using internal metrics (routes to
         destinations announced in the "IP External Reachability
         Information" field, with a metric of type "internal")
         are treated identically for the purpose of the order of
         preference of routes, and the Dijkstra calculation.

  So why do you want to see the difference between internal prefixes
 and external prefixes ? It doesn't matter for route selection.
 So I assume you want to use this to prevent "redistribution
 feedback" when doing mutual redistributing with another IGP
 at two or more places ? Or do you have another reason ?

  draft-ietf-isis-traffic-01 allows us to specify sub-TLVs for
 IP prefixes. One thing we plan to do is define a sub-TLV to
 tag or color IP prefixes. Those tags/colors can be used to
 distinquish between internal and external routes. Then you
 can use those tags/colors to control redistribution. We could
 even define one or more "well-known colors", like well-known
 BGP communities like no-advertise, etc.

    Hope this helps,

             Henk.



> Regards,
> 
> 
> Grant.
> 
> 
> -- 
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