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Router does not send Broadcast packet. that means it does not support broadcasting. but while sending packet from computer a to computer b which is not in the same network , computer a gets the mac address of default router through arp packets. and then router will send arp packets that it broadcast packets to know computer b's mac address. in this case how come router broadcast packets??? please reply as early as possibel

  • Why do you think your router doesn't use broadcasts? A router is just another host on the layer-2 network, and layer-2 ethernet requires broadcasts. – Ron Maupin Oct 22 '16 at 18:37
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    A broadcast will not go through a Router, that does not prevent the Router from sending broadcasts. – Eddie Nov 22 '16 at 4:30
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 15 '17 at 4:54
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I think you are confusing the fact that a router will not forward broadcasts with the need for a router to use broadcasts.

If PC A and PC B are in different networks with a router in between, and PC A is sending something to PC B:

  • PC A will use ARP to discover the MAC address of the default gateway, the router.
  • PC A will create frames for the packets to PC B using the router's MAC address.
  • PC A will send frames containing the packets destined for PC B to the router's MAC address.
  • The router will strip off the frames, which contain the MAC addresses, to get to the packets.
  • The router will look at the layer-3 addresses in the packets to determine to which interface it should send the packets.
  • The router will use ARP to determine PC B's MAC address on the next network.
  • The router will build new frames for the packets using PC B's MAC address.
  • The router will send the frames to PC B on the next network.
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Actually, router doesn't forward broadcast by default, when a router receive a frame with a destination mac address ff:ff:ff:ff:ff:ff wich is a broadcast.

  1. the router will compare the destination ip address to its routing table,
    1. if the router find the corresponding network on its routing table,
    2. it will send its mac address as a destination mac address to the sending host,
    3. the sending host will send the frame to the router,
    4. the router will use arp to request the the destination mac address of the pc on the other side of the network and send the frame.
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Proxy ARP is the way ARP works if the hosts involved are separated by a router.

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  • Please consider adding more details to your answer. As it is, it does not seem to answer the question. – Teun Vink Jun 10 '19 at 11:36
  • ARP would only work when a host is directly connected to a network. In scenarios where a router is in between A & B, the concept of proxy ARP comes into play ( the router accepting the broadcast and will reply back to A with its own MAC address). This is what has been explained above as well. Just the name given to is 'proxy arp'. At this point, source mac would be that of A, source IP would be that of A, destination IP would be B and the router would again issue an ARP to get B's MAC address ( no problem as it see B directly connected to it). – user11133996 Jun 11 '19 at 13:03

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