[Isis-wg] Question on TLV type 135

[Henk Smit]

> I have a question on TLV type 135 in "IS-IS extension for Traffic
> Engineering".
> 
> under the description it is told that this TLV corrects some 
> problems in existing "IP reachability TLV".
> 
> But the thing which confuses me is: Is this TLV(type 135) is aimed at
> replacing the existing IP Internal reachability TLV(type 128) and IP
> External reachability TLV(type 129).

  Yes.

> If so section 3.10.2 of RFC1195 
> "Order of Preference of Routes in the Level 2 routing" does not apply
> directly anymore because in TLV type 135 there is no bit to indicate
> "internal" and "external" routes.

  Correct.

> Also, how are we going to distinguish
> internal and external reachability.

  There is no definition of internal or external routes in the draft.
 An IP prefix is an IP prefix. If you see the same IP prefix as an
 internal and an external prefix in your IGP, you already have
 a big problem (redistribution feedback). Only doing making a
 distinction between internal/external prefixes during route
 installation is not going prevent you from problems.

  If you really want to prevent redistribution feedback, you
 need to tag the origin of your prefix. If there is a real
 interest to be able to do that, we have the sub-TLVs in TLV 135
 to do things like route coloring/tagging.

     Henk.


> I assume, extended IP reachability TLV deserves more explanation.
> 
> Regards,
> -- 
> Prashant Kumar
> Nortel Networks
> 
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