Ethernet experts,
I have basic question. I'm now studying VLAN tag for Ethernet. One field of the VLAN tag is PCP(Priority Code Point), which is 3 bit field and indicates the frame priority.
How about the priority between frame with VLAN tag and frame without VLAN tag ? I keep investigating and try to find out the description on IEEE standard (IEEE802.1Q and IEEE802.1D), however can not find out the definition yet.
Any input is highly appreciated.
John
Frames without a 802.1Q tag don't have an inherent CoS priority. If you don't assign a priority on the receiving end (by VLAN, protocol, IP, port, ...) they are handled with the default priority.
However, IP's DSCP priority has largely superseded CoS. The diffserve priority field sits in the IP header, not in the frame tag. Depending on your network equipment, DSCP values need to be mapped to CoS or vice versa for both of them to work.