The MPLS WG Archive

[Curtis Villamizar <curtis@fictitious.org>]

In message <C77B73BC1A3ED4118C2000508BAD8A7C085AC057@ma8117exch001u.inse.lucent
.com>, "Muthukrishnan, Karthik (Karthik)" writes:
> Curtis:
> 
> For the ignorant, does AFAIK stand for "As Far As I Know" ?

It has since USENET in the 1980s.

> And ".. probably.. " imply these LSRs may or may not be capable of matching
> IGP info with waiting-to-be-notified-of-failure LSPs ?

No.  "Probably" just meant that I have less confidence in the ATM
switch vendors in this area.

> Maybe a good question to ask is "which IP routers that implement
> OSPF/TE or ISIS/TE and use the flooded IGP information as a hint
> that some of the LSPs are down?". We could then take lack of an answer
> seriously.

OK.  I know for a fact that Avici does this.  Anyone else?

Since we've never explicitly tested for this, just assumed this
behaviour, it is possible that some other routers don't do this, but
this topic on the MPLS list dates back at least 5 years.

Both positive and negative responses welcome.

> John: to answer your question, pre-standard [proprietary] implementations
> such as VNN have supported this for the last decade. For more details,
> please feel free to unicast your questions to me.

Note that deployed LSRs are carrying over 1,000 MPLS/TE LSP per
direction on an interface (someone can chime in with a bigger number
if they like) so on failure, one OSPF LSA or ISIS LSPDU fragment needs
to be advertised and over 1,000 path tears on the ingress side, plus
resv tears since the same interface is the egress side of other LSPs.
Its more efficient to flood the one IGP packet upstream to the
multiple ingress that are affected than 2,000 other messages.

There is nothing magic about using the link state information to
deduce that a path is no longer feasible.  A good implementatio,
having chosen a path can add an LSP to the linked list of LSPs
dependent on each link.  When the link goes down, figuring out which
LSPs are affected amounts to walking a linked list.  Adds about 16
bytes of overhead per link in the path, but saves time on failure when
saving time matters.

> -Karthik

Curtis


> -----Original Message-----
> From: Curtis Villamizar [mailto:curtis@fictitious.org]
> Sent: Wednesday, March 12, 2003 4:21 PM
> To: Nair, Girish (Girish)
> Cc: 'john151@libero.it'; mpls
> Subject: Re: Between OSPF RSVP... 
> 
> 
> 
> In message
> <C77B73BC1A3ED4118C2000508BAD8A7C0651F476@ma8117exch001u.inse.lucent
> .com>, "Nair, Girish (Girish)" writes:
> > Giovanni,
> > 
> > I agree. Link down LSP rerouting can be done a little more efficiently
> > using the IGP. This has been done in some proprietary signaling
> > implementations
> > and works well. It involves tighter coupling between the IGP and signaling
> > though.
> > 
> > Girish
> 
> 
> There is nothing proprietary about this.  ***All*** IP routers that
> implement OSPF/TE and/or ISIS/TE do this AFAIK and probably all LSR
> that implement OSPF/TE and/or ISIS/TE (the remaining subset is mostly
> ATM switches).
> 
> I welcome corrections from anyone that knows of an LSR that implements
> OSPF/TE or ISIS/TE that doesn't use the flooded information as a hint
> that some of the LSPs are down.
> 
> Curtis
>