Check for Duplicate IP Addresses

It is common to get an IP address that is not the correct one. A sign of a duplicate IP address is seeing a DECLINE message from the client to the server.

For example:

10.40.0.0.337 > 10.42.0.58.67: BOOTP/DHCP, Request from b4:2e:99:be:1a:d3, length 301, hops 1, xid 0x9d1210d, Flags [none]
     Gateway-IP 10.252.0.2
     Client-Ethernet-Address b4:2e:99:be:1a:d3
     Vendor-rfc1048 Extensions
       Magic Cookie 0x63825363
       DHCP-Message Option 53, length 1: Decline
       Client-ID Option 61, length 19: hardware-type 255, 99:be:1a:d3:00:01:00:01:26:c8:55:c3:b4:2e:99:be:1a:d3
       Server-ID Option 54, length 4: 10.42.0.58
       Requested-IP Option 50, length 4: 10.252.0.26
       Agent-Information Option 82, length 22:
         Circuit-ID SubOption 1, length 20: vlan2-ethernet1/1/12

To test for duplicate IP addresses, ping the suspected address while turning off the node. If there continues to be responses, then there is a duplicate IP address.

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