Control traffic between switches always uses the Distributed Server Addressing model where the domain number is the last byte, with the middle byte indicates the service.

To ping the Domain DA controller the destination address is 0xfffcda.

There are no other situations that I know of where you would need to know about the domain at the end of the FCID...if you see a trace with frames like this, it's good to know how the address scheme works.

When a domain controller learns of a newly attached device on another switch, it may source a frame from 0xfffcda (da is the domain id here) to that new device as part of a discovery process. It's helpful to know that the switch that send the frame is using a for it's domain id. you may see this on the ISL between switches...or on the link to the device itself.

The only time a frame would have a destination address of 0xFFFFFC is if was a directly attached device sending a frame to the local name server. IE: registering capabilities.

Hope this helps,

Mike