Type of Service (TOS)

Iljitsch van Beijnum iljitsch at muada.com
Mon May 10 21:57:33 UTC 2004


On 10-mei-04, at 18:57, Vicky Rode wrote:

> Say if I had a qos appliance installed on networks between a lan and a 
> wan box would the qos policies be carried across wan end points (point 
> to point connection)? In other words, will the router retain the TOS 
> bits across to the other side of the wan connection to provide 
> QoS-style priority for the packets or will it clear the TOS bits?

First of all, most routers that apply quality of service mechanisms 
don't set the type of service in the process. However, many can use the 
type of service as input for their QoS decisions.

Second, routers generally pass these bits unmodified, unless 
specifically instructed to change them.

Third, these bits are often interpreted as a diffserv code point rather 
than the original type of service meaning.

One setup I've used myself is set the type of service selectively using 
a rate limit on a Cisco router, and then do traffic shaping for packets 
matching this type of service on another router. AFAIK this isn't a 
particular common setup, though.




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