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internal DHCP ip clash only on Dusseldorf UDP

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Topic Author
DudeOfLondon
Posts: 67
Joined: Sat Jan 10, 2015 5:14 pm

internal DHCP ip clash only on Dusseldorf UDP

Post by DudeOfLondon » Sat Jun 29, 2019 7:19 pm

Code: Select all

Sat Jun 29 16:19:04 2019 us=380442 Set TAP-Windows TUN subnet mode network/local/netmask = 10.66.4.0/10.66.4.254/255.255.255.0 [SUCCEEDED]
Sat Jun 29 16:19:04 2019 us=380442 MANAGEMENT: Client disconnected
Sat Jun 29 16:19:04 2019 us=380442 ERROR: There is a clash between the --ifconfig local address and the internal DHCP server address -- both are set to 10.66.4.254 -- please use the --ip-win32 dynamic option to choose a different free address from the --ifconfig subnet for the internal DHCP server
Sat Jun 29 16:19:04 2019 us=380442 Exiting due to fatal error
Hi I get the above error when connecting to the ECC-UDP_Dusseldorf server via OpenVPN program on Windows.
The Frankfurt server, for instance, works fine though.
How to fix that?

User avatar

parityboy
Site Admin
Posts: 1215
Joined: Wed Feb 05, 2014 3:47 am

Re: internal DHCP ip clash only on Dusseldorf UDP

Post by parityboy » Sun Jul 07, 2019 1:04 am

@OP

Interesting...do you not use the usual 192.168.x.x. addressing scheme on your LAN, or is this on a mobile Windows device?


Topic Author
DudeOfLondon
Posts: 67
Joined: Sat Jan 10, 2015 5:14 pm

Re: internal DHCP ip clash only on Dusseldorf UDP

Post by DudeOfLondon » Sun Jul 07, 2019 3:26 am

It's on a windows desktop PC. And I use the 192.168.2.x scheme that is provided by the router.
Meanwhile, the error isn't occurring anymore, maybe it was server-side or something else, that got mixed up.

User avatar

df
Site Admin
Posts: 415
Joined: Thu Jan 01, 1970 5:00 am

Re: internal DHCP ip clash only on Dusseldorf UDP

Post by df » Mon Sep 09, 2019 6:21 pm

Looks like there is a bug in our random IP generating code that could cause you to get assigned the internal DHCP IP as your internal client IP.
The bash code that generates the last octet for the internal IP in the server-side OpenVPN --up script is:
echo $[ 3 + $[ RANDOM % 254 ]]
The bash man page says $RANDOM is "a random integer between 0 and 32767".
That means the lowest octet is 3 (which is what we wanted), but the highest is .256, which would be invalid since that can only go up to .255.
Since we don't even want it to get to .254, I'll change the code to:
echo $[ 3 + $[ RANDOM % 251 ]]
which would still make the lowest possible octet 3, but the highest possible is now .253

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