Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

broadcast traffic on router

Does the router forward packets to all of its interfaces when it receives BOOTP DHCP, ip directed broadcast,proxy arp packets

4 REPLIES
Silver

Re: broadcast traffic on router

Yes,

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

Regards,

Dharmesh Purohit

Silver

Re: broadcast traffic on router

No. By default, routers will not forward any broadcast packets (to 255.255.255.255) 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.

New Member

Re: broadcast traffic on router

In case of directed broadcast, does it mean that the router sends the broadcast packet through a single interface until it reaches the destination network.

For proxy arp explanation does it mean that the router get's the destination ip itself by default with out forwarding the packet to all the interfaces on it?

Silver

Re: broadcast traffic on router

Suppose you have 2 networks: 172.16.2.0/24 and 172.18.2.48/24. Between these networks is a bunch of routers.

A directed broadcast would be a packet sent from 172.16.2.0 network (such as from 172.16.2.5) to 172.18.2.255. 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 172.18.2.0 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.

1050
Views
0
Helpful
4
Replies
CreatePlease to create content