CoS QoS

Coolhandluke

Hi,

Im sure quite a few people on the QoS exams can help but there must be some CCNP folk that can answer this too. When a frame is marked with a CoS value and then transferred across a trunk link, everything that I read implies that the 802.1Q info is stripped from the frame on receipt, this must include the CoS marking. I realise QoS settings could dictate how QoS information is handled but in a plain no QoS environment simply passing frames from trunk to trunk between switches, would a frame marked by a phone as CoS 5 go from switch A->B->C->D and maintain that CoS 5 Marking ?

The target environment is not cisco but am curious as to the process.

I assume that it depends on the order that the switch strips the information from a frame, i.e remove the .1q info only for ports that are untagged.

Any information is appreciated !

drkat

As far as I know the cos value on a trunk link is not stripped but only on a port that is untagged. If your target vendor isn't cisco you may have to retag the values. Generally cos/qos will match each of the link so if we're sending cos 5 out a trunk and it's received on a trunk the cos 5 will stay but if it's an access port then it will be stripped and either tagged or untagged depending on the port configuration.