Setup Guide
– For a port extender 10-Gigabit Ethernet interface, enter the keyword peTenGigE then the pe-id / stack-unit / port-id information.
– For a VLAN interface, enter the keyword vlan then a number between 1 and 4094.
NOTE: Transit trac may not be forwarded during the period when deleted ARP entries are resolved again and re-installed in
CAM. Use this option with extreme caution.
ARP Learning via Gratuitous ARP
Gratuitous ARP can mean an ARP request or reply.
During ARP learning via gratuitous ARP, the gratuitous ARP is a request. A gratuitous ARP request is an ARP request that is not needed
according to the ARP specication, but one that hosts may send to:
• detect IP address conicts
• inform switches of their presence on a port so that packets can be forwarded
• update the ARP table of other nodes on the network in case of an address change
In the request, the host uses its own IP address in the Sender Protocol Address and Target Protocol Address elds.
When a gratuitous ARP is received, the system installs an ARP entry on all three CPUs.
Enabling ARP Learning via Gratuitous ARP
To enable ARP learning via gratuitous ARP, use the following command.
• Enable ARP learning via gratuitous ARP.
CONFIGURATION mode
arp learn-enable
ARP Learning via ARP Request
The system learns via ARP requests only if the target IP specied in the packet matches the IP address of the receiving router interface.
This is the case when a host is attempting to resolve the gateway address.
If the target IP does not match the incoming interface, the packet is dropped. If there is an existing entry for the requesting host, it is
updated.
Figure 54. ARP Learning via ARP Request
IPv4 Routing
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