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RE: doubt in RFC 3031

  • From: "Alexander Marhold" <alexander@marhold.at>
  • Date: Mon, 30 Apr 2001 12:49:05 +0200
  • Cc: <mpls-ops@mplsrc.com>
  • Importance: Normal
  • Resent-Date: Mon, 30 Apr 2001 07:46:50 -0400
  • To: "Bhupesh Bajaj" <mpls@indiatimes.com>, <prabhu_b@in.huawei.com>, <asheeshj@in.huawei.com>, <srinivasch@in.huawei.com>

IMHO you are right with your statement, that normally a P-router (the
penultimate hop) does only label swapping based on the outermost label and
this a single lookup.

the sentence maybe could be better phrased in that way:
" This technique allows the egress to do a single lookup, without requiring
any additional lookup by the penultimate node "

But I think, that by reading the whole chapter the meaning of PHP is clear
and that this single sentence in his original wording put into the context
does not do any harm.

regards

Alexander Marhold
Senior Consultant
PRO IN

-----Original Message-----
From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of Bhupesh
Bajaj
Sent: Monday, April 30, 2001 12:12 PM
To: prabhu_b@in.huawei.com; asheeshj@in.huawei.com;
srinivasch@in.huawei.com
Cc: mpls-ops@mplsrc.com
Subject: doubt in RFC 3031


hi all.
while going thru RFC 3031 , in Page 18 , second paragraph says...

" This technique allows the egress to do a single lookup, and also requires
only a single lookup by the penultimate node "


isnt the penultimate node going to do a single lookup anyway...? or i have
got it all wrong..?

according to what i perceived...the penultimate node is going to look into
the label which it received and then sends the packet to the next hop
according to the information in the label it received with packet...which
means ...single lookup....

when would it do a second lookup..?

is it referring to the second lookup that the penultimate node will have to
do when it wouldnt find the label in the stack which it is expecting ...and
it will go for network layer information...?

kindly let me know.
thanks and regards,

bhupesh.
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