ARP Local Proxy Configuration
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28. ARP Local Proxy Configuration
28.1
Introduction to ARP Local Proxy function
In a real application environment, the switches in the aggregation layer are required
to implement local ARP proxy function to avoid ARP cheating. This function will restrict the
forwarding of ARP messages in the same vlan and thus direct the L3 forwarding of the
data flow through the switch.
As shown in the figure above, PC1 wants to send an IP message to PC2, the overall
procedure goes as follows (some non-arp details are ignored)
1. Since PC1 does not have the ARP of PC2, it sends and broadcasts ARP request.
2. Receiving the ARP message, the switch hardware will send the ARP request to
CPU instead of forwarding this message via hardware, according to new ARP handling
rules.
3. With local ARP proxy enabled, the switch will send ARP reply message to PC1 (to
fill up its mac address)
4. After receiving the ARP reply, PC1 will create ARP, send an IP message, and set
the destination MAC of the Ethernet head as the MAC of the switch.
5. After receiving the ip message, the switch will search the router table (to create
router cache) and distribute hardware entries.
6. If the switch has the ARP of PC2, it will directly encapsulate the Ethernet head and
send the message (the destination MAC is that of PC2)
7. If the switch does not have the ARP of PC2, it will request it and then send the ip
message.
This function should cooperate with other security functions. When users configure