Hi, I just came across an issue with DHCP. I am running an all-in-one-box setup with Neutron, ML2 and Linux Bridge. The box has a single NIC. I noticed my instances are not getting IP addresses via DHCP but when I set the IP and default gateway manually all works.

I managed to debug this issue pretty far and could find this in tcpdump:

13:23:13.458128 IP (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 308)
    0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok] BOOTP/DHCP, Request from fa:16:3e:0e:04:32 (oui Unknown), length 280, xid 0x930ba16d, secs 3, Flags [none] (0x0000)
      Client-Ethernet-Address fa:16:3e:0e:04:32 (oui Unknown)
      Vendor-rfc1048 Extensions
        Magic Cookie 0x63825363
        DHCP-Message Option 53, length 1: Discover
        Client-ID Option 61, length 7: ether fa:16:3e:0e:04:32
        MSZ Option 57, length 2: 576
        Parameter-Request Option 55, length 7: 
          Subnet-Mask, Default-Gateway, Domain-Name-Server, Hostname
          Domain-Name, BR, NTP
        Vendor-Class Option 60, length 12: "udhcp 1.20.1"
        END Option 255, length 0
13:23:13.458445 IP (tos 0xc0, ttl 64, id 18146, offset 0, flags [none], proto UDP (17), length 351)
    10.0.0.3.bootps > 10.0.0.2.bootpc: [bad udp cksum 0x1561 -> 0x00f9!] BOOTP/DHCP, Reply, length 323, xid 0x930ba16d, secs 3, Flags [none] (0x0000)
      Your-IP 10.0.0.2
      Server-IP 10.0.0.3
      Client-Ethernet-Address fa:16:3e:0e:04:32 (oui Unknown)
      Vendor-rfc1048 Extensions
        Magic Cookie 0x63825363
        DHCP-Message Option 53, length 1: Offer
        Server-ID Option 54, length 4: 10.0.0.3
        Lease-Time Option 51, length 4: 86400
        RN Option 58, length 4: 43200
        RB Option 59, length 4: 75600
        Subnet-Mask Option 1, length 4: 255.255.255.0
        BR Option 28, length 4: 10.0.0.255
        Domain-Name-Server Option 6, length 4: 10.0.0.3
        Domain-Name Option 15, length 14: "openstacklocal"
        Hostname Option 12, length 13: "host-10-0-0-2"
        Default-Gateway Option 3, length 4: 10.0.0.1
        END Option 255, length 0

You can see that the instance properly sends the DHCP Request and DNSMasq also returns a Reply but that reply shows "bad udp chksum". I googled and found the solution suggested on https://openstack.redhat.com/forum/di... working for me.

The real question is: Bug or misconfiguration?

The what I believe to be the most important config files regarding this issue can be found here: http://pastebin.com/zg5P7sxP

cheers Mathias