Backplane Utilization

Bolton07

Indicators that a loop is present in a network include:

1 'High switch backplane utilization as compared to the baseline utilization'

2 Syslog messages indicating packet looping, constant address relearning, or MAC address flapping messages

3 Increasing number of output drops on many interfaces

What do these three points mean?

Thanks


Adam

pham0329

Indicators that a loop is present in a network include:

1 'High switch backplane utilization as compared to the baseline utilization'

As it says. If the cpu on the switch is churning at 100% constantly, chances are you have a loop.

2 Syslog messages indicating packet looping, constant address relearning, or MAC address flapping messages

When there's a loop in the network, the CAM can get corrupted because it's constantly updating the mac address. For example, SW1 is connected to SW2 via fa 0/1 and fa 0/2

When Host A on Sw1 sends a broadcast

• SW1 forwards the broadcast out both port fa 0/1 and fa 0/2
• SW2 receives the frame on fa 0/1 first, and it records the source MAC address of host A in its CAM table, and associate it with port fa 0/1
• SW2 then receives the 2nd frame, now on port fa 0/2. SW2 sees that it already has an entry in its CAM table for host a's MAC address so it update the entry to associate host a with fa 0/2
• both frames are forwarded back out to SW1
• SW1 receives the frame and does the same thing and this continues

3 Increasing number of output drops on many interfaces

I'm not sure about this one. Maybe because the switch is too busy processing the broadcast, it's doesn't have enough resource for anything else?