Quote:
Originally Posted by derspot  U ROCK !
I have a question.
When we use the weights, limits and guarantees in QOS RULES THAT ARE UNDER A Class Of service, do these ( weights etc ) apply only to:
1. Already TOS Market Traffic.
2. Apply only to connections that match the QOS Rule that is under the QOS class but not necessarily are marked beforehand.
3. These weights are shared among all QOS Rules INCLUDING Rules that are outside THE QOS CLASS.
AS A BEST PRACTICE ARE WE SUPPOSED TO "ATTACH" THE QOS Classes Only to the External Interfaces ( Inbound and Outbound ) as found in the literature ? |
Only the second statement fits to your question. For instance, if you have one FW A and FW B. And on FW A, you have a QoS rule that labels all FTP packets with the DSCP of 100110, then on FW B the FTP packets come with the DSCP of 100110. But, if you create a QoS Rule on FW B for FTP with the sam DSCP, FW B will re-write the same DSCP into the FTP packet.
As I can tell from my experience, there is no possibility to create a QoS rule which only looks into the IP header to decide what to do with. So, already marked packets will be re-marked again. This point could be one aspect for CP developers as a "request for enhancement".
It is commonly indeed the best practice to attach the QoS class only to the external interface. Otherwise, all packets coming from I to o will be re-marked again, which could be considered as wasting performance!
Yasushi