Introduction to Inverse, Reverse and Proxy ARP- Address Resolution Protocol

Today I am going to talk about Inverse ARP, Reverse ARP and Proxy ARP. As many of you guys already knew about the ARP so called as Address Resolution Protocol. Here in this article I am going through the Inverse ARP, Reverse ARP and Proxy ARP one by one.

Inverse ARP

Let me tell you a little bit about Inverse ARP protocol. So Inverse ARP is generally used in the ATM networks and is enabled by default. It forms an ATM map entry and is required to drive unicast packets to relay agent or server on the other side of an association. Inverse ARP is maintained only for the aal5snap encapsulation type.

For multipoint interfaces, an IP address can be learned using other encapsulation types since broadcast packets are used. Though, unicast packets to the other side will stop since there is no ATM map record and thus DHCP renewals and discharges also stop.

Fig 1.1- Inverse, Reverse and Proxy ARP

Reverse ARP

Now after Inverse ARP, we can talk about Reverse ARP protocol, Reverse ARP mechanism is the same way as the Address Resolution Protocol (ARP), but that the RARP appeal packet desires an IP address instead of a media access control (MAC) address. 

RARP repeatedly is used by diskless workstations as this sort of device has no way to stock IP addresses to use when they boot. The only address that is known is the MAC address as it is burned in to the hardware.RARP needs a RARP server on the similar network segment as the device interface.

Since there are limitations with RARP, many industries use Dynamic Host Configuration Protocol (DHCP) to allocate IP addresses dynamically. DHCP is economical and needs less maintenance than RARP.

Proxy ARP

Proxy ARP is generally used to permit devices that are disconnected into physical network segments associated by a router in the same IP network or subnetwork to undertake IP-to-MAC addresses. 

When boxes are not in the identical data link layer network but are in the similar IP network, they attempt to communicate data to each other as if they were on the local network. Though, the router that divides the hardware boxes and will not direct a broadcast message since routers do not pass hardware-layer broadcasts. Therefore, the addresses cannot be resolved.

When proxy ARP is deactivated, a device replies to ARP demands received on its interface only if the target IP address is the same as its IP address or if the target IP address in the ARP appeal has a statically configured ARP alias.

Globally Disabling Proxy ARP

RouteXP_R1> enable

RouteXP_R1# configure terminal

RouteXP_R1 (config)# ip arp proxy disable

RouteXP_R1 (config)# end

Disabling Proxy ARP on an Interface

RouteXP_R1> enable

RouteXP_R1# configure terminal

RouteXP_R1 (config)# interface GigabitEthernet0/1

RouteXP_R1 (config-if) # no ip proxy-arp

RouteXP_R1 (config)# end

Clearing the ARP Cache

RouteXP_R1> enable

RouteXP_R1# clear arp interface Gigabitethernet0/1

RouteXP_R1# clear arp-cache

RouteXP_R1# exit

Configure ARP entry limit globally

RouteXP_R1> enable

RouteXP_R1# configure terminal

RouteXP_R1 (config)# arp entries interface-limit 1 log 1

RouteXP_R1 (config)# exit

Configure ARP entry limit on an interface

RouteXP_R1> enable

RouteXP_R1# configure terminal

RouteXP_R1 (config)# interface Ethernet 0/1

RouteXP_R1 (config-if) # ip address 10.10.10.1 255.255.255.0

RouteXP_R1 (config-if) # arp entries interface-limit 1 log 1

RouteXP_R1 (config-if) # exit

Verifying the ARP Configuration

RouteXP_R1# show arp

RouteXP_R1# show ip arp

RouteXP_R1# show processes cpu | include (ARP|PID)