Re: 6PE-Alt

[Francois Le Faucheur IMAP <flefauch@cisco.com>]

On 31 Jan 2008, at 15:25, Vishwas Manral wrote:

> Hi Francois,
>
> The document I have written does not use signaling

It is a bit of a stretch to claim that 6PE-Alt does not use signaling.
6PE-Alt and 6PE both use MP-BGP to signal IPv6 reachability.  6PE-Alt  
would simply save you one field (the label value) inside the same  
advertisement.

On the other hand, 6PE-Alt would restrict operations to only one of  
the options allowed in 6PE. The reasons 6PE allowed multiple label  
allocation is precisely because different PEs may want to use  
different label allocation policies.  For example, one 6PE router may  
prefer to allocate per-prefix label in order to be able to forward  
packets via label switching as opposed to performing IPv6 lookup. 6PE  
allows each PR router to use whatever label allocation scheme it sees  
best.


> and does not define
> a new AFI/SAFI functionality to achieve the 6PE.

It is a bit of a stretch to imply that 6PE defines a new AFI/SAFI.
6PE uses the IPv6 AFI and the SAFI defined in RFC3107 (which for  
memory dates back from 2001) precisely for the purpose of binding an  
MPLS label when advertising IPv6 reachability.

> The difference is obvious, we get the same functionality

my impression is that you get a restricted subset of the  
functionality (ie forcing every router to use that single label  
allocation scheme). This had been discussed before and decided that  
such a restriction was undesirable and unnecessary.

> without
> adding any new signaling mechanism.

my impression is that both use the same MP-BGP signaling mechanism  
except one would save a few bytes in the same MP-BGP advertisements.

There are multiple interoperable implementations of 6PE today and am  
not aware of significant issues with the current 6PE control plane.

Cheers

Francois