From: Peter van Oene (pvo@usermail.com)
Date: Mon Oct 06 2003 - 01:35:28 GMT-3
PHP is signalled with 3.
At 09:07 PM 10/5/2003, Snow, Tim wrote:
>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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