broadcast traffic on router

Unanswered Question
purohit_810 Thu, 08/09/2007 - 11:19


Also you can use DHCP Relay agent. What relay agent does.... It convert broadcast into unicast and forwards to DHCP server.


Dharmesh Purohit

wochanda Thu, 08/09/2007 - 11:46

No. By default, routers will not forward any broadcast packets (to on any segment is connected to. You have the option of configuring ip helper-address on your interface to forward broadcast DHCP/BOOTP packets to a particular host via unicast, but we wont flood out all of our interfaces.

In the case of directed broadcast, the router doesn't necessarily know that the packet is destined for a broadcast address. Usually this packet will be forwarded across the network until it gets to the destination segment, where it is broadcasted at the routers discretion (only on that segment).

As for proxy-arp packets, these are usually originated by routers. If we did get one, though, we would process it and not forward it.

wochanda Thu, 08/09/2007 - 19:27

Suppose you have 2 networks: and Between these networks is a bunch of routers.

A directed broadcast would be a packet sent from network (such as from to This is a 'directed broadcast' because the destination subnets information is in the destination IP, but it points to the broadcast address. In this case, the packet would be forwarded as any other unicast packet until it gets to the router with the network. This last router can then decide whether to send the packet out its interface as a broadcast, or drop it.

Since proxy-arp is an ARP packet, it is never forwarded from one interface to another on a router.


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