Hello Azm
It all depends on the practical application. If the following criteria are met:
- If you are only using only two markings and nothing else will be marked on your network
- if no additional marked traffic will be entering your network
- if your marked packets are not entering other networks
If all of the above is true, then it doesn’t matter what markings you place on your packets. If there are two markings, you will prioritize each type in a specific way. You can have it AF11 and AF21 if you like. As long as you are reacting to each type of priority in the way which will deal with the congestion you are experiencing.
Now the best practices that are put into place are there in order to have a common method of prioritization so that in the event of the interconnection with other networks, the priorities and DSCP values being use are already normalized and compatible. If you are a completely autonomous system and there is no case where you will be sending marked packets to networks not managed by you, you can use any markings you like.
I hope this has been helpful!
Laz