BASICS – PROXY ARP
Its very important for routing and is enabled default in IOS.
Its method by which router made himself available to the host.How ?
|——-ROuter——|
| |
PC1 PC2
IP 10.10.20.1/24 10.10.40.1/24
Consider that HostA(10.10.20.1/24) want to send traffic to HostB of diff subnet (10.10.40.1/24).
Host A neither have any default gateway configured nor it knows how to reach router.It will send arp request for 10.10.40.1,local router
when receives the request and also know how to reach subnet 10.10.40.0,will reply arp with its own hardware address.
Host A will see this reply, cache it, and send future IP packets for host B to the gateway. The gateway will forward such packets to
host B by the usual IP routing mechanisms. The gateway is acting as an agent for host B, which is why this technique is called “Proxy ARP”; we will refer to this as a transparent subnet gateway or ARP subnet gateway.
ARP cache entries generally shows multiple ip address are mapped to single hardware addresss ,It that case proxy arp is used and single hardware addresss is of router interface and multiple ip address is of hosts.
