ARP Throttling
ARP throttling is a tool to limit ARPs into a VLAN. ARPs, you may recall,
are sent as broadcast. Once an ARP is sent for a given IP, the switch prevents
repetitive ARPs for a short period of time:
�¡ First packet to destination forwarded to Route Processor.
�¡ Subsequent traffic dropped until MAC is resolved.
�¡ It prevents overwhelming the Route Processor (RP) with redundant
ARP requests.
�¡ It helps during Denial of Service attacks.
�¡ It is removed when MAC is resolved in two seconds.
Configuring and Troubleshooting CEF
By default, CEF is on and supports per destination load sharing.
To disable CEF:
�¡ 4500.Use (config)#no ip cef.
�¡ 3500/3700.On each interface, use (config)#no ip routecache
cef.
�¡ 6550 with policy feature card, distributed FC, and multilayer switch
FC.Cannot be disabled.
View CEF information with the following:
#show interface fastethernet 2/2 | begin L3
View switching statistics with the following:
#show interface fastethernet 2/2 | include switched
View FIB with the following:
#show ip cef
View detailed CEF FIB entry with the following:
#show ip cef fastethernet 2/2 10.0.0.1 detail
Troubleshoot CEF drops with the following:
#debug ip cef drops
Troubleshoot packets not forwarded by CEF with the following:
#debug ip cef receive
Troubleshoot CEF events with the following:
#debug ip cef events