Local bridge with DHCP

Post your questions about SoftEther VPN software here. Please answer questions if you can afford.
Post Reply
tcdaly
Posts: 3
Joined: Tue Aug 13, 2019 6:52 pm

Local bridge with DHCP

Post by tcdaly » Mon Aug 30, 2021 3:28 pm

When creating a local bridge, the SoftEther documentation recommends that the network interface bridged to is not allocated an IP address. The local bridge configuration also requires a DHCP server. In my case, I have no option but to run the DHCP server on the same Linux box as SoftEther and the local bridge.

However the DHCP server seems to expect an IP address allocated to the network interface it is bound to. I cannot see a way of running the DHCP server without an IP address.

How important is it not to have an IP address allocated to the network interface?

eddiewu
Posts: 135
Joined: Wed Nov 25, 2020 9:10 am

Re: Local bridge with DHCP

Post by eddiewu » Mon Aug 30, 2021 3:37 pm

This recommendation is for those who bridge the virtual hub to an existing server side LAN segment. The server can either be or not be part of it. Therefore, there must be an working DHCP server.

tcdaly
Posts: 3
Joined: Tue Aug 13, 2019 6:52 pm

Re: Local bridge with DHCP

Post by tcdaly » Mon Aug 30, 2021 5:39 pm

Thank you. I can see no way of implementing a working DHCP server unless the NIC that is bridged to has an IP address assigned to it.

tcdaly
Posts: 3
Joined: Tue Aug 13, 2019 6:52 pm

Re: Local bridge with DHCP

Post by tcdaly » Tue Aug 31, 2021 8:46 am

If you consider this DHCP server configuration fragment:

Code: Select all

subnet 10.1.1.0 netmask 255.255.255.0 {
  range 10.1.1.50 10.1.1.99;
  option routers 10.1.1.1;
  option broadcast-address 10.1.1.255;
}
If the network interface has no IP address, the DHCP server has no means of associating the subnet with the interface. So the server fails to start with the error:

Code: Select all

Aug 29 22:33:08 lillie dhcpd[835]: Not configured to listen on any interfaces! 
Aug 29 17:58:19 lillie dhcpd[2527]: No subnet declaration for eth1 (no IPv4 addresses).
Aug 29 17:58:19 lillie dhcpd[2527]: ** Ignoring requests on eth1.  If this is not what
Aug 29 17:58:19 lillie dhcpd[2527]:    you want, please write a subnet declaration
Aug 29 17:58:19 lillie dhcpd[2527]:    in your dhcpd.conf file for the network segment
Aug 29 17:58:19 lillie dhcpd[2527]:    to which interface eth1 is attached. **

eddiewu
Posts: 135
Joined: Wed Nov 25, 2020 9:10 am

Re: Local bridge with DHCP

Post by eddiewu » Tue Aug 31, 2021 11:57 am

I said it is only relevant to who has a working LAN on the server side. If you don’t then you are not relevant.

cedar
Site Admin
Posts: 1700
Joined: Sat Mar 09, 2013 5:37 am

Re: Local bridge with DHCP

Post by cedar » Mon Sep 13, 2021 11:08 pm

If the local bridge is connected to a tap device, you should set the IP address.

You can also set an IP address if you are locally bridging to a physical NIC, but be aware that that IP address cannot communicate with the Virtual Hub.
When operating purely as a bridge, it is estimated that the CPU load can be reduced by disconnecting the TCP/IP stack of the OS without setting the IP address. (Although this estimation is doubtful)

Post Reply