Subject: ILM mappings

From: "Trilok Chand" <[email-masked]>
Date: Mon, 8 May 2000 15:55:02 +0530

Hi,
        Can anybody tell where can i get information about choosing an ILM mapping when there are multiple NHLFEs existing for an incoming label?

Thanks in advance,
TrilokChand

---

From: Eric Gray <[email-masked]>
Date: Mon, 8 May 2000 09:50:57 -0700

TrilokChand,
 
    An interesting question.  How did there get to be multiple
NHLFEs for a single incoming label?  Suspending disbelief
on this for a moment, however, and supposing there was a
reason for this to happen - the implementer must have had
some plan for demultiplexing the single label to determine
which NHLFE would be used.  One way might be to pop the
label and look at what comes after it - but a pop instruction
should be a single NHLFE (with - in this case - a next hop 
of "self").  Is there a useful application for this scenario?
 
    It seems to me that there would not be multiple NHLFE
entries for a single label as this will defeat the purpose for 
having a label.  But, even if there was a reason to do this,
the implementation that causes this to happen is the same
implementation that has to deal with the outcome.
 
    If you shoot yourself in the foot, it will hurt. :-)
 
--
Eric Gray

-----Original Message-----
From: Trilok Chand [mailto:[email-masked]]
Sent: Monday, May 08, 2000 3:25 AM
To: [email-masked]
Subject: ILM mappings

Hi,
        Can anybody tell where can i get information about choosing an ILM
mapping when there are multiple NHLFEs existing for an incoming label? 
 
Thanks in advance,
TrilokChand

---

From: Eric Gray <[email-masked]>
Date: Mon, 8 May 2000 11:22:40 -0700

Shahram,

	I guess I should have said -

	"If you shoot yourself in the foot, it will hurt -
	but as long as you don't miss, it isn't my problem."

	See comments in line.  In general, however, as soon
as you have an application, you have the answer to the 
original question.  Clearly, you can have a reason to shoot
yourself in the foot. :-)

> From: Shahram Davari [mailto:[email-masked]]
> Sent: Monday, May 08, 2000 10:53 AM
> To: 'Eric Gray'; 'Trilok Chand'
> Cc: [email-masked]
> Subject: RE: ILM mappings
> 
> 
> Hi Eric,
>  
> There are two scenarios that a single label may correspond to multiple
> NHLFEs:
>  
> 1) Some part of an LSP is E-LSP and another part is L-LSP

I think you would have to have at least two labels - one for 
(each) L-LSP and one for a corresponding E-LSP.  It's quite
reasonable to use the same NHLFE for all packets using the
same label in an E-LSP as long as the next hop information 
would be the same - since the E-bits are used to determine
the queuing behavior relative to forwarding these packets to
the next hop.  It is also quite reasonable to treat the EXP
bits as part of the label (in the E-LSP case) for the purpose
of determining the NHLFE that applies.

But that's quibbling.  I concede that this may be a use for
having multiple NHLFEs corresponding to a single incoming 
label.

> 2) In case of Multicast.

Conceded.

However, in both of these cases, the resolution to be used
is built right into the application it is used for.  In the
first case, the EXP bits are used to differentiate one NHLFE
from another.  In the second case, all NHLFEs are used.  It
could be argued that a combination scenario may also occur.
This application also has its own built in answer.

>  
> Regards,
> Shahram Davari 
> Product Research 
> PMC-Sierra Inc. 
> 555 Legget drive, 
> Suit 834, Tower B, 
> Ottawa, ON K2K 2X3, Canada 
> Phone: +1 (613) 271-4018 
> Fax  : +1 (613) 271-7007 
>     
> 
> From: Eric Gray [mailto:[email-masked]]
> Sent: Monday, May 08, 2000 12:51 PM
> To: 'Trilok Chand'
> Cc: [email-masked]
> Subject: RE: ILM mappings
> 
> 
> TrilokChand,
>