dhcp server will not start on "dummy" interface

[cwahlin]

I am tring to set up a central DHCP server for a large WLAN network. All client requests are forwarded b routers around the network, so there are no broadcast requests.

Anyway, we like to set up our servers with a physical address, and then dummy addresses behind it for the services that the server runs (easier to move services around between servers). So, this is what I have:

dummy0 Link encap:Ethernet HWaddr 32:45:59:F1:07:87
inet6 addr: fe80::3045:59ff:fef1:787/64 Scope:Link
UP BROADCAST RUNNING NOARP MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:210 (210.0 b)

dummy0:4 Link encap:Ethernet HWaddr 32:45:59:F1:07:87
inet addr:172.21.127.4 Bcast:172.21.127.4 Mask:255.255.255.255
UP BROADCAST RUNNING NOARP MTU:1500 Metric:1

dummy0:14 Link encap:Ethernet HWaddr 32:45:59:F1:07:87
inet addr:172.21.127.14 Bcast:172.21.127.14 Mask:255.255.255.255
UP BROADCAST RUNNING NOARP MTU:1500 Metric:1

eth0 Link encap:Ethernet HWaddr 00:08:74:92:AE:7B
inet addr:172.21.127.34 Bcast:172.21.127.47 Mask:255.255.255.240
inet6 addr: fe80::208:74ff:fe92:ae7b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:36496 errors:0 dropped:0 overruns:0 frame:0
TX packets:86 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2569172 (2.4 MiB) TX bytes:12817 (12.5 KiB)
Interrupt:18 Base address:0x8c00

The DHCP server does not want to start on the dummy interfaces!! Why is this? I can send dhcp requests to the dummy address, but the server replies with the eth0 address.

The ifcfg for the dummy interface looks like this:

DEVICE=dummy0:14
IPADDR=172.21.127.14
NETMASK=255.255.255.255
ONBOOT=yes

I have also tried to force the DHCP server to start on the dummy interface with DHCPDARGS set to dummy0:14 but I get the following error:

No subnet declaration for dummy0:14 (no IPv4 addresses).

But I do have it declared in the conf!

subnet 172.21.127.14 netmask 255.255.255.255 {
}

Anyone? I have googled but found no answer...

/Carl

[zackf]

Call me a layman but if your subnet mask is 255.255.255.255 in dhcpd.conf what addresses is it supposed to assign?

[cwahlin]

We are relaying dhcp requests from other subnets to this DHCP server. This is what one of the subnets might look like:

subnet 10.140.137.0 netmask 255.255.255.0 {
range 10.140.137.5 10.140.137.250;
option routers 10.140.137.1;
option broadcast-address 10.140.137.255;
option subnet-mask 255.255.255.0;
option domain-name-servers 172.21.127.4;
}

This works fine. But since I am relaying DHCP requests to the dummy0:14 interface, I would like the server to reply with this address instead of the eth0 interface like it is doing now. Just makes firewall rules much cleaner, and if we ever move the dhcp service to a different machine, we will not have to change the firewall rules, just move the dummy0:14 interface.

/Carl

[jrummy27]

I had this same problem a year or so ago and I don't think I ever got past it. Try adding the interface to /etc/sysconfig/dhcpd like so

DHCPDARGS="dummy0:14"

If that doesn't work and you do figure it out, please post your solution since I remember pulling my hair out on this one

[cwahlin]

Tried that, but that is when I get the error: "No subnet declaration for dummy0:14 (no IPv4 addresses). "

/Carl

[jrummy27]

Ah sorry I missed that part. I have no clue then

[rampuji]

i am new here.

some one please tell me step by step from starting.


Thanks
Rampuji