implicit - explicit label values

Hi group,

I have a question regarding the implicit and explicit label values. We all
know that

-a label value of 0 stands for the ipv4 explicit null label
-a label value of 2 stands for the ipv6 explicit null label
-a label value of 3 stands for the ipv4 implicit null label

O.k., fine until now.

My question is why is there no label value for the ipv6 implicit null label?
Or with other words, why is there a special label value for the ipv6
explicit null label?

My assumption is that since with the explicit null label, the egress LSR
(PE) receives a labeled packet and if he already knows while "checking the
label" whether it is an ipv4 or an ipv6 packet after popping the label, he
already knows in which table he has to do the lookup, the operation goes
much quicker instead of just popping the label and then checking if it is
ipv4 or ipv6. A bit similar like the Ethertype in the Ethernet Frame.

On the other way, with the implicit null label, due to the PHP at the egress
LSR (PE) gets the packet unlabeled and can already do the decision between
ipv4 / ipv6. So no need to create a special label value for ipv6 implicit
null label.

Can someone bring light into this????

Roger #23543

BTW: In the example above, I was thinking about mpls labeled ip traffic, not
vpn traffic since this would require the additional vpn label.

Blogs and organic groups at http://www.ccie.net
Received on Tue Feb 09 2010 - 13:38:38 ART