Re: [PCN] RSVP and ECMP

The problems obviously show up if the load balancing device does not 
inspect the RSVP traffic.
Then, you cannot ensure that the signaling traffic follows the data 
traffic anymore.

Also with tunnels you need to ensure that at least one of the tunnel 
endpoints is aware of the signaling protocol. This might seem to be a 
simple requirement but I assume in reality it is not that easy. This is 
the area where complexity says HELLO to path-coupled signaling.

Ciao
Hannes

PS: When you still think that it is totally trivial then you might want 
to look at the many tunneling schemes folks use or want to use.

Georgios Karagiannis wrote:
> Hi Bruce, Hi all
>
> I agree with Bruce! If it is to use probing, then we have to ensure
> that the probes should get the similar correct ECMP treatment as the
> correct ECMP treatment achieved by RSVP.
>
> This means that the probe messages have to have the same addresses and
> ports as the data.
> I think tat this is not difficult and not complex to be achieved.
>
> Best regards,
> Georgios
>
>
>
> On 10/23/2007, "Bruce Davie" <bdavie@cisco.com> wrote:
>
>   
>> 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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