Host A wants to send something to Host B who is in a different network. Between them is Router 1. Host A sends an ARP broadcast but Router 1 is not answering it. Why is that so?
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1Not sure what you mean. Host A would ARP to find the MAC of Router 1 and the router would reply. Host A could then encapsulate the frame and forward it towards the router. Are you saying if Host A sends a broadcast in its subnet why the router does not forward that to Host B?– Daniel DibDec 2, 2013 at 17:56
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1if you truly have host a and host b in different networks, could you check their netmasks? It sounds like the netmask on host a is wrong– Mike PenningtonDec 2, 2013 at 18:27
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1 Answer
The router will not do this by default, unless you enable Proxy ARP on that router's interface(s), but best practices dictate Proxy ARP should be disabled wherever possible.
However, host A should know by analyzing its own subnet mask (binary AND against its own subnet mask and Host B's address) that Host B is on a different network, and instead send the traffic to its default gateway (if one is configured), and if necessary, Host A will ARP for its default gateway's MAC address, which the router should respond to when appropriate.
answered Dec 2, 2013 at 17:58
