From: Snow, Tim (timothy.snow@eds.com)
Date: Sun Oct 05 2003 - 22:07:29 GMT-3
Hey all. I'm working on the last test for CCIP and I have a question
regarding RFC 3032 - MPLS Label Stack Encoding
When Penultimate Hop Popping is used, the ultimate PE router will send a
label to the Penultimate router signaling that router should POP the label
and send the datagram as unlabeled IP.
My question is which one of these labels is the one that's sent to the
penultimate router, the MPLS/VPN architecture book says 3.
i. A value of 0 represents the "IPv4 Explicit NULL Label".
This label value is only legal at the bottom of the label
stack. It indicates that the label stack must be popped,
and the forwarding of the packet must then be based on the
IPv4 header.
iv. A value of 3 represents the "Implicit NULL Label". This
is a label that an LSR may assign and distribute, but
which never actually appears in the encapsulation. When
an LSR would otherwise replace the label at the top of the
stack with a new label, but the new label is "Implicit
NULL", the LSR will pop the stack instead of doing the
replacement. Although this value may never appear in the
encapsulation, it needs to be specified in the Label
Distribution Protocol, so a value is reserved.
Also, if anyone can provide some information as far as good study links for
this test, I would greatly appreciate it.
Tim
Timothy Snow
CCIE #12042
EDS - DOW Network Operations
MS 3B
1075 W. Entrance Drive
Auburn Hills, MI 48326
Phone:+1-248-754-7900
mailto:timothy.snow@eds.com
pager: 888-351-4584
www.eds.com
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