Re: 6PE-Alt

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

Hi Vishwas,

I think I've brought up my main points in the previous message so  
will leave it at that for now.

On 31 Jan 2008, at 18:29, Vishwas Manral wrote:

> Hi Francois,
>
> As the 6PE-Alt does not require any additional functionality from
> BGP-IPv6 (yes that is the signaling required - but that is the same
> required for normal BGP IPv6. For 6PE we use a new AFI/ SAFI and send
> labels uselessly. So please do not say that the claim no signaling
> changes are required for 6PE-Alt  is a stretch), and that is why we
> have inter-operable implementations of 6PE-Alt too. It is not about
> interoperable implementations alone though. I however am surprised how
> this simple mechanism was not captured earlier in the review or coding
> process.
>
> We do not need to transport labels at all which are now being
> transported. Also as the peer decides the label I use, we may have to
> configure different labels from different peers (thus using bigger
> keys/ more memory in the tables and a lot of other overload). There is
> a lot of overhead of signaling and dataplane without any necessity.
>
> I also have issues with the 6VPE RFC too but let us tackle issues one
> at a time. Also please note 6VPE has the concept of VRF's and is used
> to give VPN services, while VPE is used for basic IPv6 connectivity
> over MPLS IPv4 coulds. So please do not confuse the 2.

I didn't really feel confused about the 2, but thanks for the advise ^)

Cheers

Francois

> Thanks,
> Vishwas
>
> On Jan 31, 2008 8:53 AM, Francois Le Faucheur IMAP  
> <flefauch@cisco.com> wrote:
> > 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