The MPLS WG Archive

[Vach Kompella <vkompella@JasmineNetworks.com>]

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.

-Vach