Subject: Re: Scaling hierarchical LDP/PW stitching

From: Mustapha Aissaoui <[email-masked]>
Date: Mon, 02 Aug 2004 18:15:57 -0400

Richard and Dimitri,
this issue is in my view one of the critical issues. I believe a
workable solution should have the following characteristics:

1. State how stitching nodes are discovered. I do not agree with
Peter that a stiching node is just another LSP switching node. There
are PW specific operations to be performed in the data, control, and
management (OAM) planes on a PW segment.

2. State how routing of PW control messages are performed once the
stitching nodes have been discovered. It seems to me that a solution
that mandates the use of FA-LSPs is too restrictive.

3. Avoid if possible making the PW label routable. Not that I have
anything against that but if a solution turns PWs into routable
entities on their own, then we should discuss it in that wider
context. In that case, the use of tunnel LSPs becomes a convenience
as opposed to a requirement of the architecture.

Regards,
Mustapha.  
----------
[email-masked] wrote:
> 
> Dimitri,
> 
> > > b. FA-LSP are mandated to connect SNs. This is restrictive in my
> > > view. It is not clear to me how non FA-LSPs could be used as tunnel
> > > LSPs.
> >
> > the questions turns out to be if i have a set of FA-LSPs and a set of
> > tunnels LSPs, the former being advertized as FA links but not
> > the latter
> > how does the global mechanism work ?
> >
> > the response is be setting up a routing adjacency on top of
> > the tunnels
> > LSPs that can not be advertized as FA LSPs
> >
> > so, on one side, advertize these LSPs as simple IP/MPLS links so that
> > the non-FA capable nodes see these links (also i assume here
> > that a FA
> > capable node is also "non-FA" capable)
> >
> > and on the other side, for non-FA capable nodes to see established FA
> > LSPs, mandate that FA link advertisement are beforehand
> > translated into
> > common IP/MPLS link advertisement
> >
> > note: as we're at the bottom of the stack here there is also
> > no level issue
> 
> Please can you elaborate as to how this solves the problem Mustapha raises? If I understand correctly, Mustapha is raising the issue that if non FA-LSPs (e.g. LDP LSPs) are used then they are not advertised via the IGP as tunnels (P2P links), and therefore can not be used in the same way that FA-LSPs can be used to establish MH-PWs. This would be the case if a provider only used LDP LSPs or used LDP LSPs in conjunction with TE LSPs for different traffic types. In the latter case, some PWs will need to be tunnelled over the FA-LSPs, and some of the PWs will need to be tunnelled over the LDP LSPs, i.e. they will follow separate paths.
> 
> Your solution appears to just mandate that FA link advertisements are advertised as common IP/MPLS link advertisements so that they can be processed by non-FA capable nodes. This still requires FA-LSPs to be provisioned and therefore does not address the issue of using non-FA LSPs for tunnelling PWs.
> 
> Thanks,
> Richard

---

From: dimitri papadimitriou <[email-masked]>
Date: Tue, 03 Aug 2004 00:49:07 +0200

richard,

[email-masked] wrote:

>>>  view. It is not clear to me how non FA-LSPs could be used as
>>> tunnel LSPs.
>> 
>> the questions turns out to be if i have a set of FA-LSPs and a set
>> of tunnels LSPs, the former being advertized as FA links but not 
>> the latter how does the global mechanism work ?
>> 
>> the response is be setting up a routing adjacency on top of the
>> tunnels LSPs that can not be advertized as FA LSPs
>> 
>> so, on one side, advertize these LSPs as simple IP/MPLS links so
>> that the non-FA capable nodes see these links (also i assume here 
>> that a FA capable node is also "non-FA" capable)
>> 
>> and on the other side, for non-FA capable nodes to see established
>> FA LSPs, mandate that FA link advertisement are beforehand 
>> translated into common IP/MPLS link advertisement
>> 
>> note: as we're at the bottom of the stack here there is also no
>> level issue
> 
> 
> Please can you elaborate as to how this solves the problem Mustapha
> raises? If I understand correctly, Mustapha is raising the issue that
> if non FA-LSPs (e.g. LDP LSPs) are used then they are not advertised
> via the IGP as tunnels (P2P links), and therefore can not be used in
> the same way that FA-LSPs can be used to establish MH-PWs. This would
> be the case if a provider only used LDP LSPs or used LDP LSPs in
> conjunction with TE LSPs for different traffic types. In the latter
> case, some PWs will need to be tunnelled over the FA-LSPs, and some
> of the PWs will need to be tunnelled over the LDP LSPs, i.e. they
> will follow separate paths.
> 
> Your solution appears to just mandate that FA link advertisements are
> advertised as common IP/MPLS link advertisements so that they can be
> processed by non-FA capable nodes. This still requires FA-LSPs to be
> provisioned and therefore does not address the issue of using non-FA
> LSPs for tunnelling PWs.

there are several point to clarify from the above, in particular re - 
stating the question that was "how non FA-LSPs could be used as tunnel 
LSPs." the question boils down to "how a set of FA-LSPs and a set of 
tunnel LSPs (i.e. non FA-LSPs), the former being advertized as FA links 
but not the latter how does the global mechanism work ?" on the other 
side the question turns out to be having established a FA-LSP how do i 
make the existence of the correspond link information to nodes that do 
not under stand "FA links" - you're making another distinction which is 
for the non-FA LSPs are they "TE LSPs" or "LSPs" and the response is 
that it only dependent on the PE capability to advertize the corr. link 
that can further be used by other nodes to tunnel PWs

coming to your last statement, it boils down to what you do today, more 
precisely, the fact that FA-LSPs are provisioned or triggered doesn't 
impact the non-FA LSPs are used for tunneling PWs

thanks,
- dimitri.

> Thanks, Richard
> .