Reverse ARP protocol and proxy

I have learned a lot about ARP, but I don't know what you know. Now let's take a look at the reverse and proxy content about the ARP protocol. First, we need to understand these two concepts.

Reverse ARP Protocol

Reverse ARPReverse ARP, RARP) is used to convert the MAC address of the physical address to the corresponding IP address. For example, when a diskless workstation is started, it cannot obtain its own IP Address Configuration information from its operating system. In this case, the diskless workstation can send a broadcast request to obtain its own IP address information, while the RARP server responds to the IP request message-assign an unused IP address to the diskless workstation by sending an RARP response packet ).

Reverse ARPRARP) has been replaced by BOOTP and DHCP to a large extent. The later two protocols improve RARP by providing more information besides IP addresses, such as the IP address of the default gateway and DNS server.

Proxy ARP Protocol

Proxy arpproxy arp) is also known as the hybrid ARPPromiscuous ARP) RFC 925 and 1027) is generally used by devices like routers to answer ARP requests from hosts in another network segment.

The following is an application of proxy ARP. The host pc1190000000066/24) needs to send packets to the host pc2192.168.000020/24, because the host PC1 does not know the existence of the subnet and is in the same network segment as the target host pc2. therefore, host PC1 sends an ARP request to broadcast packets to the MAC address of 192.168.20.20. In this case, the vro identifies the destination address of the packet as another subnet. Note that the IP address of the router interface is configured with a 28-bit mask. Therefore, the vro returns its hardware address 0004 to the requesting host. dd9e. cca0 ).

Then, PC1 sends the packets sent to PC2 to the interface E0/0 of the MAC address 0004. dd9e. cca0 router. The router forwards the packets to the target host pc2. Next, the router will send data packets to pc2 ). This ARP Protocol makes the subnet network topology transparent to the host, or it can be said that the router spoofs the source host PC1 with an invalid PC2 MAC address ).

Proxy ARP