Serving Multiple Subnets on one NIC, and two vNICs

Adam Wolfe kadamwolfe at
Wed Aug 1 08:43:15 UTC 2012

I am in the middle of setting up a new dhcp server between 3 subnets, 
using ubuntu 10.04.

The subnet that eth0 is connected to is and will not use dhcp 
at all.

The subnet that eth0:26 is connected to is, eth0:37 is on

I see dhcp discover, request, ack and offer all happening in 
/var/log/syslog, but the client never picks up an address.  It simply 
sits there doing it's dhcp discover.  I'm fairly certain this has to do 
with the routing as I am able to ping the address on eth0, but not 
eth0:1 eth0:2

My routing table is:

Kernel IP routing table
Destination     Gateway        Genmask         Flags   MSS Window irtt Iface     U         0 0          
0 eth0     U         0 0          
0 eth0
10.8..26.0     U         0 0          
0 eth0               UG        0 
0          0 eth0               UG        0 
0          0 eth0               UG        0 
0          0 eth0

Does anyone have some experience or expertise on what routes should be 
in place?  I'm practically positive on my dhcp.conf, it was copied from 
another, already working, server.  It just seems like it doesn't know 
where it should be sending the info to, but it is trying.  It also 
cannot ping other devices on the 26 and 37 subnets.

I was also wondering how to overcome the 'not configured to listen on 
any interfaces' caused by adding "INTERFACES="eth0 eth0:26 eth0:37" " to 
/etc/default/dhcp-server.  I don't necessarily need this option added, 
but it might be nice for future growth to eliminate chatter.

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