If you are seeing drops and flushes on a physical interface, sniff the VLAN in which you have the interface or the interface itself. If you are seeing drops/flushes on the VLAN interfaces, you will need to sniff the MSFC internal port. However, unlike Sup2/MSFC2, in a Native IOS Sup720, you cannot SPAN the MSFC3 internal port but there is a way to capture the packets hitting the CPU using built in Packet buffer tool(This feature is like having an internal packet sniffer built into the switch. It allows you to save to memory a copy of the packets contained in an asic’s buffer so that they can be analyzed). Here is how you do it.
1) Enable “service internal” mode
switch# config t
switch(config)#service internal
switch(config)#exit
2) Set up the what you want to monitor. Say the Sup720 is in slot 5.
switch# show platform capture buffer asic pinnacle slot 5 port 4 direction out priority lo
switch# show platform capture buffer asic <---- used to verify the config
3) Start capturing traffic. In this example we will capture for the next 10 seconds:
switch# show platform capture buffer collect for 10
switch# show platform capture buffer status <---- used to verify the config
4) After waiting 10 seconds use the next 2 commands to view the packets saved to memory:
switch# show platform capture buffer data filtered <----- gives a one line summary for each packet saved
switch# show platform capture buffer data sample [sample#] <------ gives the detail (vlan, mac & IP addresses, etc) of each sample packet
After you are done, disable service internal
switch# config t
switch(config)#no service internal
switch(config)#exit
Hope this helps
