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I'm trying to do a network install of Ubuntu 12.04 on Cisco UCS C240 rack-mounted servers, using Cobbler for the provisioning. Cobbler is managing my DHCP server (ISC), which is configured to hand out fixed IP addresses based on the MAC address of the server. Here's a relevant section from /etc/dhcp/dhcpd.conf that cobbler auto-generates:

group {
    host generic4 {
        hardware ethernet 2a:2c:b2:b4:f7:1a;
        option host-name "compute-3";
        option subnet-mask;
        option routers;
        filename "/pxelinux.0";

The machine (compute-3) is able to PXE-boot successfully and start the Ubuntu installation process. However, when the installer reaches the part where it tries to acquire an IP address via DHCP, it fails. (At this point, if I manually configure the networking with the same IP address/netmask and gateway, the installation completes sucessfully).

When I examine /var/log/syslog on the cobbler node that runs the DHCP server, I see that the server offers an IP address, but it is declined by the client:

Mar 11 21:51:03 compute-1 dhcpd: DHCPDISCOVER from 2a:2c:b2:b4:f7:1a via eth2
Mar 11 21:51:03 compute-1 dhcpd: DHCPOFFER on to 2a:2c:b2:b4:f7:1a via eth2
Mar 11 21:51:03 compute-1 dhcpd: DHCPREQUEST for ( from 2a:2c:b2:b4:f7:1a via eth2
Mar 11 21:51:03 compute-1 dhcpd: DHCPACK on to 2a:2c:b2:b4:f7:1a via eth2
Mar 11 21:51:03 compute-1 dhcpd: DHCPDECLINE of from 2a:2c:b2:b4:f7:1a via eth2: not found

From what I have read, a client will send a DHCPDECLINE after doing an ARP probe to see if another machine on the network already has the offered IP address. I think Ubuntu's installer uses udhcpc from BusyBox, and from looking at the code, that seems to be what udhcpc does.

However, when I use arping from the cobbler node, I cannot locate any other machines on that network which have That is, until the DHCP process starts for the install, after which time I do see that compute-3's MAC address, 2a:2c:b2:b4:f7:1a, is associated with that IP address.

# arping
60 bytes from 2a:2c:b2:b4:f7:1a ( index=0 time=118.017 usec
60 bytes from 2a:2c:b2:b4:f7:1a ( index=1 time=74.148 usec
60 bytes from 2a:2c:b2:b4:f7:1a ( index=2 time=48.876 usec

What are the possible failure modes that could lead to this behavior? Why would the client think somebody else has that IP address? Or, why else it might it be declining the address?

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Do you have a firewall on dhcp server ? Do you have other logs ? – Dom Mar 12 '13 at 7:54
Nope, confirmed that there's no firewall. Can you suggest what other logs I should be examining for this, other than the DHCP server logs that are shown above? – Lorin Hochstein Mar 12 '13 at 14:36
up vote 3 down vote accepted

I found in Google a similary problem :

You have an error in your router option : it is not in the same subnet, so it can't be discovered.

option routers instead of option routers

Hope this help !

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