Openvpn server on Asus Merlin router ip allocations


Occasional Visitor

Previously my open vpn server always allocated ip addresses to clients as, 10, 14, and 18.

I thought maybe something to do with the explanation by JanJust here:

Yesterday after resetting the router it allocated .1 and .2 instead of the expected .6 and .10.

This plays havoc with my sync and rtrr jobs on the client NAS’s.

What have I done. :)



Part of the Furniture
That's a very old thread, when the net30 topology was the default. But OpenVPN is now changing the default topology to subnet in most cases (NOT unless the server has specifically configured net30). So if you updated the firmware recently, it may be that you're NOW being allocated from the subnet, starting w/ .2 and moving upward .3, .4, etc.

Here's a dump from 386.4 clearly showing a subnet topology by default.

[email protected]:/tmp/home/root# cat /tmp/etc/openvpn/server1/config.ovpn | grep topology
topology subnet

In such cases, you'll need to either explicitly add net30 to the custom config field ...

topology net30

... or else change your ifconfig-push directives to use a subnet specification ...


I believe the plan w/ OpenVPN is to eventually deprecate net30 completely, so perhaps now is a good time to get off that topology anyway.


Asuswrt-Merlin dev
I switched topology to subnet years ago. According to the OpenVPN manual:

The recommended topology for modern servers. Note that this is not the current default. Addressing is done by IP & netmask.

This is the old topology for support with Windows clients running 2.0.9 or older clients. This is the default as of OpenVPN 2.3, but not recommended for current use. Each client is allocated a virtual /30, taking 4 IPs per client, plus 4 for the server.


Occasional Visitor
Thanks very much. Really appreciated. I will have a think about whether to embrace the new or specify the old.


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