InformationDisable proxy ARP on all interfaces.
Address Resolution Protocol (ARP) provides resolution between IP and MAC Addresses (or other Network and Link Layer addresses on none IP networks) within a Layer 2 network.
Proxy ARP is a service where a device connected to one network (in this case the Cisco router) answers ARP Requests which are addressed to a host on another network, replying with its own MAC Address and forwarding the traffic on to the intended host.
Sometimes used for extending broadcast domains across WAN links, in most cases Proxy ARP on enterprise networks is used to enable communication for hosts with mis-configured subnet masks, a situation which should no longer be a common problem. Proxy ARP effectively breaks the LAN Security Perimeter, extending a network across multiple Layer 2 segments. Using Proxy ARP can also allow other security controls such as PVLAN to be bypassed.
Organizations should plan and implement network policies to ensure unnecessary services are explicitly disabled. The 'ip proxy-arp' feature effectively breaks the LAN security perimeter and should be disabled.
SolutionDisable proxy ARP on all interfaces.
hostname(config-if)#no ip proxy-arp