Proxy ARP

Proxy ARP is the technique in which one host, usually a router, answers ARP requests intended for another machine.

Topology :-

ARP Table

• In this topology you can see i have two network

1. 10.0.0.0 /24
2. 20.0.0.0 /24

• Here we have some MAC address of particular Devices 

Interface	IP address	MAC Address
R1 F0/0	10.0.0.10	c201.08fc.0000
R1 F0/1	20.0.0.10	c201.08fc.0001
R2 F0/0	10.0.0.1	c202.1f84.0000
R3 F0/0	20.0.0.1	c203.1d28.0000

• After successfully pinging from R2 to R3 when we check the ARP table we are getting this result in R2

R2 Device 

Protocol  Address          Age (min)     Hardware Addr   Type   Interface

Internet  10.0.0.1                -                c202.1f84.0000      ARPA   FastEthernet0/0

Internet  20.0.0.1                0               c201.08fc.0000       ARPA   FastEthernet0/0

• In this Output we can see the MAC address of 20.0.0.1 is c201.08fc.0000 but in actual this MAC is belong to 10.0.0.10 ip address.
• Means this MAC address is belong to Gateway IP 10.0.0.10
• Our R1 is work as a Gateway for 10.0.0.0 network and 20.0.0.0 network.
• When we are resolving arp request for 20.0.0.1 that time our Gateway say this IP's MAC address is my MAC address.
• Means Router is giving answer respect of R3.
• It's called Proxy ARP. 
• Same as for R3 device.

R3 Device

Protocol  Address          Age (min)     Hardware Addr     Type   Interface
Internet  10.0.0.1                1               c201.08fc.0001     ARPA   FastEthernet0/0
Internet  20.0.0.1                -                c203.1d28.0000    ARPA   FastEthernet0/0

• In this Output we can see the MAC address of 10.0.0.1 is c201.08fc.0001 but in actual this MAC is belong to 20.0.0.10 ip address.
• Means this MAC address is belong to Gateway IP 20.0.0.10