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    [SOLVED] "Interface matches multiple shared networks" when I enable DHCP servers on 172.20.0.1/24 and 172.20.1.1/24

    Scheduled Pinned Locked Moved DHCP and DNS
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    • R
      rprichard
      last edited by rprichard

      Forgive me if this is a rookie mistake, but I cannot figure out what's going on here.

      I have my LAN on 172.20.1.1/24 with DHCP from 172.20.1.100-172.20.1.199, and everything works like a charm. I also had interfaces with associated DHCP servers in the 172.20.100.1/24 and 172.20.255/24 ranges, though they are currently disabled.

      I am trying to add DHCP to my DMZ interface, which is on 172.20.0.1/24 with DHCP from 172.20.0.100-172.20.0.199. Based on the ranges, it seems like this should not be a problem as the range is non-overlapping with my existing 172.20.1.1/24 interface.

      However, after a long troubleshooting process I've realized DHCP dies the second I enable the DHCP server on DMZ. The log produces an error "Interface igb0 matches multiple shared networks." LAN is on igb0; DMZ is on igb1. I can set DMZ to any other address range (e.g. 172.20.2.1/24) and it works fine. It also works fine with DMZ on 172.20.0.1/24 and with the LAN DHCP server disabled.

      Is this a bug, or am I doing something wrong? Or is there something magic about the 172.20.0.1/24 range?

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      • R
        rprichard
        last edited by

        Solved! I found another thread discussing this problem, and the original poster tracked it down to a virtual IP that was on the wrong interface. Sure enough, I had a virtual IP on the LAN interface pointing to an address on the DMZ interface.

        How bizarre!

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