forward of packets destined to 255.255.255.255

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Jul 3rd, 2003
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Hi,


I'm a CCIE but I'm still dump. :)

Under which conditions does a router forward a packet destined for 255.255.255.255?


Regards

Alex


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thisisshanky Thu, 07/03/2003 - 06:38
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Alex,


By default every router blocks or drops broadcasts. If you configure a helper address, That should help forwarding broadcasts received on a particular interface to another network.

glen.grant Thu, 07/03/2003 - 09:38
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Or apparently in some earlier versions of IOS the router would forward these packets by mistake due to a bug , just saw this the other day on 11.0.17 code where a device was answering to broadcast yet the traffic was able to get off the subnet to it's destination .

7rbowenii Mon, 07/07/2003 - 11:43
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Alex,

There are such things as directed and undirected broadcasts. a message sent to 255.255.255.255 should not traverse the subnet it's on. However, this is not so with a bad IOS or an IP Helper statement (it gets a little more complicated but, we'll save that.). A directed broadcast is one that is sent to a different subnet, but the subnet is specified. I'm sure the guys will correct me if this is incorrect. So a directed broadcast would be such that subnet A is 10.0.1.0/24 and subnet B is 10.0.2.0. A client on subnet A sends a broadcast to the IP 10.0.2.255 it should be forwarded. I hope this helps.



-Bo

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