CODEWITHSUNDEEP
ipethernetlanarp
user1673206
user1673206

Reputation: 1711

ARP beyond its LAN

Does someone knows why ARP cannot send messages beyond it's LAN? I have two scenarios:

  1. computer A -> router -> computer B
  2. computer A -> router -> router -> computer B

In the first scenario the ARP works, if A wants to know B's MAC address, it sends ARP to the router, who sends ARP to B (if the router also doesn't know B's MAC address).

In the second scenario it is not possible.

It will be great if someone knows the answer.

Upvotes: 1

Views: 673

Answers (1)

Kannan Mohan
Kannan Mohan

Reputation: 1850

ARP protocol is meant for fetching/resolving layer 2 address (MAC) from layer 3 address (IP). The ARP is used only for layer 2 communication and not used above it. And so if a data needs to be passed between devices within a local network then layer 2 level of communication is enough i.e communication happens with MAC and IP is used to get the destination host's MAC id.

As routers operate only on layer 3 they dont pass layer 2 broadcasts out of their networks.

Having said that, your first scenario worked based on a concept called "Proxy ARP" in which two devices which belongs to same layer 3 address (IP) but are separated by router. In such scenario router acts as a proxy and helps in resolving ARP request.

Adding more routers between devices in the same network will make things complicated and might require some specific configuration in them.

It is not a good practice to have devices in same network (IP) separated by routers. Thats a poor network design.

Upvotes: 1

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