Sunday, August 10, 2008

The DHCP Bad Address Saga.

For some time now we've been working on an issue that resulted in "Bad Address" being reported in the DHCP console.

The client was getting an address successfully but this lease did not get registered in the database and hence not in the MMC. When the next client came along it was assigned an address already in use. Conflict detection was enabled and hence BAD_ADDRESS was recorded.

When the Bad Address is noted. The column that should contain the MAC address contains something different. This is the IP Address in hex and reversed. Example :

After lots of troubleshooting it was found that there two machines that had something wrong with their cable. Since removing these two cables from the sub net, the issue has gone away.

With hindsight, we could have got an idea that the issue was a rogue machine earlier. The network covered 3 class C subnets. If we'd split them, we'd have seen the issue was one just one of them. This was one of those suspicions that crossed our mind but didn't follow up.

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