Re: implicit - explicit label values

The implict null specification is not specfic to ipv4.

The corrected descriptions:

-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 implicit null label

-- 
<ruhann>
CCIE (R&S)
blog.ru.co.za
On Tue, Feb 9, 2010 at 2:38 PM, Roger Pfaeffli <rpf23543_at_gmail.com> wrote:
> 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.
>
>
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