The MPLS WG Archive

[Bora Akyol <akyol@pluris.com>]

John

When we implemented our fast reroute algorithm, we had to deal with 
both numbered and unnumbered interfaces, numbered interfaces were 
much easier to deal with as you avoided two of the steps that I 
explained below. Basically, when you calculate the exclusion list, 
the numbered interfaces make it trivial, whereas unnumbered 
interfaces require judicious use of the TE database as I describe 
below.

How did you implement the fast reroute algorithm when you had 
unnumbered interfaces?

Bora

At 5:46 PM -0800 2/27/01, John Drake wrote:
>Bora,
>
>Without trying to be difficult, your response to Bala sounds suspiciously
>like an assertion.  Wouldn't the intermediate node processing, with respect
>to accesses of the TE database, be the same whether dealing with unnumbered
>or numbered links?  So if we don't need router ID for numbered links, why do
>we need it for unnumbered links?   
>
>Thanks,
>
>John 
>
>-----Original Message-----
>From: Bora Akyol [mailto:akyol@pluris.com]
>Sent: Tuesday, February 27, 2001 4:30 PM
>To: Bala Rajagopalan
>Cc: 'Bora Akyol'; mpls@UU.NET
>Subject: RE: New Internet Draft on ERO
>
>
>At 5:41 PM -0500 2/27/01, Bala Rajagopalan wrote:
>>   >
>>>   Think of an unnumbered ERO of the form <1,1,1,1,1,1,1,1>
>>>
>>>   Now somewhere in the middle, an LSR wants to calculate a fast reroute
>>>   LSP. Normally, one would ask the TE database the simple question of
>>>   avoid my next hop and would give the router ID of the next hop, but
>>>   in this case, first you have to find out who the router at the end of
>>>   the egress interface is. This is not hard, then you need to find out
>>>   who the router that is right after the immediate hop. This second one
>>>   is harder since you have to make a query into the TE database, to
>>>   find that. Then you have to make a third query into TED, to calculate
>>>   an LSP that avoids the immediate next hop but merges as soon as
>>>   possible with the main LSP. And finally, you calculate an ERO that
>>>   now is a mixture of both numbered and unnumbered interfaces possibly
>>>   and initiate signaling. As I describe here, this is not undoable, but
>>>   at what cost.
>>>
>>>   If one adds the extra four bytes of router ID as part of the ERO (as
>>>   we did in the EERO) this whole thing becomes trivial to implement.
>>>
>>
>>Just curious, to implement this type of fast reroute, can't intermediate
>>nodes
>>get downstream information from record route?
>>
>>Bala
>
>Bala
>
>As I wrote in my previous email, there are other ways of getting this
>info. The point that I was trying to make is that when you add the
>router ID, things become clearer and simpler.
>
>Bora