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I have 2 bridges (vmbr1 vmbr2) on proxmox server.

vmbr1 IP: 192.168.106.1 for NAT clients

vmbr2 IP: 192.168.107.1 for Local only

I have set up DHCP server (isc-dhcp-server) and it works perfectly with one network segment (on vmbr1).

When I attempt to set the second segment (vmbr2), DHCP server fails with the message:

No subnet declaration for vmbr2 (no IPv4 addresses). ** Ignoring requests on vmbr2. If this is not what you want, please write a subnet declaration in your dhcpd.conf file for the network segment to which interface vmbr2 is attached. **

for this error this statement apparently should fix the issue:

subnet-mask 255.255.255.0;

However then the error becomes this:

 isc-dhcp-server.service: Control process exited, code=exited, status=1/FAILURE If you think you have received this message due to a bug rather isc-dhcp-server.service: Failed with result 'exit-code'. than a configuration issue please read the section on submitting Failed to start LSB: DHCP server. bugs on either our web page at www.isc.org or in the README file before submitting a bug. These pages explain the proper process and the information we find helpful for debugging. exiting.

Here is the working /etc/default/isc-dhcp-server:

INTERFACESv4="vmbr1" #INTERFACESv4="vmbr1 vmbr2" #INTERFACESv6=""

Here is the working /etc/dhcp/dhcpd.conf:

option domain-name "mydomain.ca"; option domain-name-servers 8.8.8.8,8.8.4.4; subnet 192.168.106.0 netmask 255.255.255.0 { range 192.168.106.20 192.168.106.150; #subnet-mask 255.255.255.0; option routers 192.168.106.1; } #subnet 192.168.107.0 netmask 255.255.255.0 { #range 192.168.107.20 192.168.107.150; #subnet-mask 255.255.255.0; #option routers 192.168.107.1; #}

The options causing issue are commented out.

Any ideas?

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No, it's not asking you to add a line

subnet-mask 255.255.255.0;

There is no such directive as subnet-mask. What you were thinking was probably option subnet-mask; however, it's not required because the mask is already specified in the subnet declaration (i.e. the subnet x.x.x.x netmask y.y.y.y { ... } block).

The No subnet declaration for vmbr2 means that dhcpd wants to see a subnet ... { ... } block with a network address and mask that match the settings vmbr2 is currently configured to.

Here's a corrected version of your working dhcpd.conf ready to serve two subnets:

option domain-name "mydomain.ca"; option domain-name-servers 8.8.8.8,8.8.4.4; subnet 192.168.106.0 netmask 255.255.255.0 { # <-- subnet mask already specified here range 192.168.106.20 192.168.106.150; ##subnet-mask 255.255.255.0; <--- this line should be deleted option routers 192.168.106.1; } subnet 192.168.107.0 netmask 255.255.255.0 { # <-- subnet mask already specified here range 192.168.107.20 192.168.107.150; ##subnet-mask 255.255.255.0; <--- this line should be deleted option routers 192.168.107.1; }

You are apparently viewing the error messages through the systemctl status isc-dhcp-server.service output. You should be aware that it shows only the last 10 lines of the actual output. A much better way to verify the correct syntax of your DHCP server configuration would be to use the -t option of dhcpd.

When I saved your original "working /etc/dhcp/dhcpd.conf" as /tmp/dhcpd.conf.test, uncommented the first subnet-mask line and ran dhcpd -cf /tmp/dhcpd.conf.test -t, here is the full output:

# dhcpd -cf /tmp/dhcpd.conf.test -t Internet Systems Consortium DHCP Server 4.4.1 Copyright 2004-2018 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ /tmp/dhcpd.conf.test line 6: semicolon expected. subnet-mask 255. ^ Configuration file errors encountered -- exiting If you think you have received this message due to a bug rather than a configuration issue please read the section on submitting bugs on either our web page at www.isc.org or in the README file before submitting a bug. These pages explain the proper process and the information we find helpful for debugging. exiting.

Note that the verbiage at the end probably caused you to miss the important part:

/tmp/dhcpd.conf.test line 6: semicolon expected. subnet-mask 255. ^ Configuration file errors encountered -- exiting

indicating that the subnet-mask should not be used like that.

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  • The "working" version that you suggested was the first I tried, however id did not work, providing me with the first error. Later on I looked up for the solution. Commented Dec 18, 2022 at 16:36
  • Interestingly, after removing all extra lines when I run " dhcpd -cf /etc/dhcp/dhcpd.conf -t " or "dhcpd -cf /etc/dhcp/dhcpd.conf -t vmbr1 vmbr2", no errors are shown. But If I do "service isc-dhcp-server restart", the "service isc-dhcp-server status" does show the error \ Commented Dec 18, 2022 at 16:43
  • Then you'll need to run journalctl -xeu isc-dhcp-server.service to view the complete journal of that service, and if necessary, use the up-arrow key to scroll back to see if there is more than one error involved. Sometimes when an error is detected while parsing a configuration file, it throws off the parser and may cause spurious errors afterwards... and if you only check service isc-dhcp-server status = systemctl status isc-dhcp-server, you may not see all the messages produced by the service. Commented Dec 19, 2022 at 1:40

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