override the client broadcast bit?

Marc Perea marccp at srttel.com
Tue Sep 7 17:05:03 UTC 2010

Hello list,
I have an ISP environment where I suspect my access gear is stomping out some broadcast traffic that I'd rather it didn't, but probably does so for security reasons. Our general case uses a modem that sets the broadcast bit (flag) in the Discover to 0's (false), which results in everything working fine and dandy through our relay agents. We're trying to add a new type of modem to the network, and it is this device's normal operation to set the broadcast bit true (0X800 I think in the sniff), which is a problem. When the Offer gets back to the relay agent access gear, I believe it is getting bit bucketed due to it being a broadcast at layer 2 instead of unicast to a MAC like our other modem's request.
Dhcpd clearly has no trouble honoring either a unicast or broadcast response, so my question is: can we force the server to only respond with a unicast, even if the client requested a broadcast response? Getting new firmware on the modem may or may not pan out, but we're also going down that road, FYI. Being able to force the server into unicast mode would still be a useful tool though.
Has anyone else had any experience with this - any tales to tell?

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