IOS - PROXY ARP - HOW WORK ?

 IOS - PROXY ARP - HOW WORK ?

Proxy ARP - "On behalf of Other means Proxy"

Proxy ARP is a technique by which a proxy server on a given network answers the Address Resolution Protocol (ARP) queries for an IP address that is not on that network. The proxy is aware of the location of the traffic's destination and offers its own MAC address as the (ostensibly final) destination.

Here, we will explain Proxy ARP with an example. For our Proxy ARP example, we will use the below topology.

PC  A /B/C/D  and PROXY ROUTER  all Configured with Static IP address , without no IP Proxy ARP 

TEST from PC A to PC C or PC D is not reachable , But all Gateway Reachable 

On Proxy Router

PROXY ARP DISABLED 

Ping is working for Own Gateway for PC but not for Other Subnet Gateway "NO ROUTING ENBALED"

DEBUG ARP Information , ARP Broadcast but no Reply for Destination MAC.

Now Let see what happen when we enable PROXY ARP on interface toward PC A and B Proxy ARP Router.

NOW AGAIN TEST SAME PINGS 

Now we can see we are able to ping after enable proxy ARP , Proxy ARP router Says PC A let me Proxy your packets to Other Subnet.

When you check the ARP , you notice MAC address for PC D and C are same as Proxy Router MAC, This means Proxy Router giving it MAC for redirect the Packet.

PROXY ROUTER MAC - 

DEBUG ARP shows First Packet hold and ARP packet send Broadcast on Layer 2 MAC and Proxy Router Respond with it Own MAC for IP 172.16.1.4 , and then Destination MAC change from Broadcast to PROXY ROUTER 

See in Packet capture Source/Destination MAC and IP 

Good to Understand the Proxy ARP ,