I have a network where I have three servers in the DMZ that need to talk to two servers on the LAN and visa versa. The DMZ switch is a 3750, The next hop towards the LAN servers is an ASA 5520. After that there is a Cisco 4507 and then finally we get to the LAN switch which is another 3750. So all and all, there are 4 network devices.
My very limited understanding of QoS is I need to configure all 4 devices for QoS correct?
Does having the FW in the middle change anything in my QoS strategy?
I want to keep this as simple as possible. Can I use source and destination addresses to state what should get priority on the devices?
Yes QoS is setup across the entire network, up to a QoS "boundary". The boundary is where you will setup QoS Categorizations and QoS Marking of cos(802.3 cos bits), dscp (differentiated services code point), and ip precedence (Layer 3 TOS bits), in this case the ethernet port where the server is connected. The internal parts of the network are usually set to trust all packets markings, therefore, queueing and packet switching is faster, and less configuration intensive. Attached is a document that covers the QoS strategy.
Having the Firewall in the middle has no effect on the strategy, only on the trusted state of each port (i.e. inside, outside, dmz).