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After having experienced a rather malicious attack on our corporate network by someone running a rogue DHCP server, I'm wondering if there's any way to prevent this from happening again?
Ask your ethernet switch/bridge or cablemodem vendor for a method of disabling non-ARP broadcasts from being received by client machines. You can then trust your switches to direct such requests only to anything you let receive broadcasts, which should only be trusted servers. Cisco's IRB bridging has "subscriber-policy" which roughly approximates this that I use for our DSL customers. I believe their higher-end switches can take layer-2 access-lists, which could be made to work similarly. Any protocol that relies on trusting the first server to reply to a broadcast is similiarly vulnerable. I'm not sure theres a way to secure the protocol itself if the client has zero knowledge of the network its on when it starts up, which is the point of DHCP. Note that disabling broadcasts may adversely affect some already-broken protocols, such as WINS or SMB. This might only prevent shares off of "client" machines from showing up in others' Network Neighborhood, but I can't say that I've tested it. Aaron Hopkins aaron@cyberverse.com Chief Technical Officer, Cyberverse Inc. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBN5qJmUfJWHAEvsjBAQHa/QP/TnuMtu17O2wn5F15fFITHdCUDOCLUqy1 4QyfzRLdyeNFQA5o5bSoPirP3DjgPb2s5l/0IgQjJDPPMehCnFNCQ7sFq/A3/+3I 3e7XsxASmHXDsxbQP490oPbKkfMEvtAXH9pYolwnfmuhxn/VPYXqOg4A1GomukBp PQlYBTOnSL0= =77jy -----END PGP SIGNATURE-----