Re: [PCN] RSVP and ECMP

Michael,
  RSVP tries to forward the Path exactly the same way that it would  
forward the data. Since Path messages are processed outside of the  
fast path, it is possible for the router to look at anything that is  
in the path message, including source addr, dest addr, and port  
numbers, and figure out where a data packet that had those values in  
its IP header would get forwarded. It sends the Path message out that  
interface. In practice, this takes care of the vast majority of ECMP  
algorithms. This approach is implemented today.

  If ECMP was using something from the IP or higher layer header that  
was not in the Path message, then a problem would arise.

  So, practically speaking, if the probe messages have the same  
addresses and ports as the data, they should get correct ECMP
treatment. Or at least, fare no worse than RSVP.

Bruce

On Oct 23, 2007, at 12:07 PM, Michael Menth wrote:

> Hi,
>
> I've got a question regarding RSVP. PATH messages need to be  
> carried over the same path as subsequent data packets. How is this  
> achieved in the presence of ECMP routing? In theory, PATH messages  
> can take a different route than data packets if the load balancer  
> takes arbitrary parts of the header(s) to calculate a suitable hash  
> value, which decides which route the packet will take.
>
> This issue seems to be related to the problem of how to make sure  
> that PCN probe messages take the same path as subsequent PCN data  
> packets, provided that they have the same source and destination  
> ports and addresses.
>
> I am interested in how this problem is solved in practice or  
> whether it is intentionally avoided.
>
> Regards,
>
>    Michael
>
> -- 
> Dr. Michael Menth, Assistant Professor
> University of Wuerzburg, Institute of Computer Science
> Am Hubland, D-97074 Wuerzburg, Germany, room B206
> phone: (+49)-931/888-6644, fax: (+49)-931/888-6632
> mailto:menth@informatik.uni-wuerzburg.de
> http://www3.informatik.uni-wuerzburg.de/research/ngn
>
>
>
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