Proxy ARP is a protocol utilized in Routers by default and works towards the rule of default gateway configuration requirement on the tip hosts.
Instance State of affairs: Proxy ARP
Let’s take a lab situation instance to have clear understanding of how proxy ARP works. Under are 3 units linked in sequence i.e. R1, R2 and R3 respectively.
We’ll configure Routers R1 and R3 in several subnets and having no default gateway as under –
R1#
!
no ip routing
!
interface FastEthernet0/0
ip deal with 192.168.12.1 255.255.255.0
R2#
!
interface FastEthernet0/0
ip deal with 192.168.12.2 255.255.255.0
!
interface FastEthernet0/1
ip deal with 192.168.23.2 255.255.255.0
!
no ip routing
!
interface FastEthernet0/0
ip deal with 192.168.23.3 255.255.255.0
Now lets ping from R1 (which has no default gateway) to achieve R3.
Sort escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.23.3, timeout is 2 seconds:
!!!!!
Success price is 100% (5/5), round-trip min/avg/max = 68/100/144 ms
R1#
R1#sh arp
Protocol Handle Age (min) {Hardware} Addr Sort Interface
Web 192.168.12.1 – c200.1988.0000 ARPA FastEthernet0/0
Web 192.168.23.3 21 c201.1988.0000 ARPA FastEthernet0/0
The above output was a hit since R1 was in a position to ping R3 . Nevertheless, “Present ARP” command on R1 exhibits two IPs ie 192.168.12.1 and 192.168.23.3 having the identical mac deal with (on this case c201.1988.0000). That is fishy and now want to seek out out the place is the mac deal with truly residing.
Under , we test the mac deal with of interface fa0/0 which is linked to R1 Router.
R2#sh int fa0/0 | i bia
{Hardware} is Gt96k FE, deal with is c201.1988.0000 (bia c201.1988.0000)
Now we perceive that R2 acts as a proxy for requests coming from R1 and destined for different subnet. R2 offers its personal mac deal with within the ARP reply and therefore forwards the packets on behalf of R1 to R3 and vice versa.
Now , lets see what occurs once we disable proxy ARP on each the interfaces of R2 –
R2(config)#int fa0/0
R2(config-if)#no ip proxy-arp
R2(config-if)#int f0/1
R2(config-if)#no ip proxy-arp
After clearing the ARP cache of R1, the output is under –
R1#clear arp
R1#ping 192.168.23.3
Sort escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.23.3, timeout is 2 seconds:
…..
Success price is 0 % (0/5)R1#sh arp
Protocol Handle Age (min) {Hardware} Addr Sort Interface
Web 192.168.12.1 – c200.1988.0000 ARPA FastEthernet0/0
Web 192.168.23.3 0 Incomplete ARPA
R1#
As realized from this take a look at, after disabling proxy ARP on R2 , it has stopped performing as proxy for Interfaces Fa0/0 and Fa0/1 on which R2 and R3 are linked.
