The MPLS WG Archive

[Yakov Rekhter <yakov@juniper.net>]

Vach,

> I apologize if this has been discussed ad nauseam.  I looked through the
> archives before venturing out on the subject, and couldn't find an
> (explicit) answer to the question: why isn't the router ID in the ERO, and
> how come 6.3 of the rsvp-unnum draft says:
> 	"If, after processing and removing all initial subobjects in the ERO
> that refer to itself, the receiving node find a subobject of type Unnumbered
> Interface ID, it determines the next hop as follows..."
> 
> I can understand the router ID not being there makes it more concise, at the
> expense of being a little less readable, and requiring a little more
> processing at the receiving end.  In the interest of clarity and easier
> processing, I'd have eaten the 4 byte hit.  But that's something the WG can
> vote (has voted?) on.
> 
> The other aspect is the first clause of the quoted sentence above from the
> rsvp-unnum draft: "all initial subobjects that refer to itself."  Suppose
> the ERO is made up of Unnum links (1, 1, 1, 1, 1), i.e., a series of hops,
> each of which used their Interface #1 outbound.  Processing according to
> 6.2, a receiving node would strip out the first subobject, after validating
> that it received the ERO over its PHOP's interface #1.  Then, by the
> statement above, it looks at the next one which coincidentally appears to
> refer to itself also.  If I'm not missing something here, this first hop
> removes all the subobjects before it is done, which is not what is was
> intended.  With a router ID in each subobject, the ERO would look like ((r1,
> 1), (r2, 1), (r3, 1), (r4, 1), (r5, 1)), which would remove the ambiguity.
> 
> Can someone clarify?  Thanks.

The text needs to be clarified to say something like "all initial subobjects
of type other than Unnumbered Interface ID"...".

Yakov.