I have a 2851ISR with 256MB of memory using adventerpriseK9 12.4(11)XW5. 2 weeks ago I began monitoring the buffers and I have noticed buffer misses on small buffers, middle buffers, Big buffers, and Verbig buffers. I then looked at Cisco's documentation on tweaking the buffers and used their rules for each buffer. However, I'm still noticing buffer misses and failures. Fortunately, the failures are not because of memory. The CPU is always under 10% and mostly under 3%. I used the show buffers assigned command and noticed there are a lot of buffers allocated to a dot11 interface. This interface is bridged using irb. When I perform a show buffers leak, the dot11 interface has alot of entries. Is this normal for a bridged interface? And since the CPU and memory do not seem to having issues, should I worry about buffer misses and failures?
1) You need to classify the traffic
2) You need to mark that traffic
3) You need to allocate bandwidth or limit user traffic.
The problem with QoS is that you taking away from some application to give to another application. I don't have a clear picture of your network so I can't make a recommendation nor I'm planning to. QoS is one of those features where you need a full understanding of your network else something may break.
I highly suggest you take a moment and read the QoS documentation and see which method works best for your environment.