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[Openvpn-users] running on same port as NTP

  • Subject: [Openvpn-users] running on same port as NTP
  • From: Florin Andrei <florin@xxxxxxxxxxxxxxx>
  • Date: Mon, 26 Nov 2007 17:26:37 -0800

I guess I can do some tests myself, but let me ask first, just in case 
it's something that was already tested:

Due to some restrictions that I cannot change, the only UDP port that I 
can use from a certain location to connect to my OpenVPN server at home 
is NTP (123/udp).
Now, the OpenVPN server also runs ntpd, which is synchronizing to 
various servers in the pool.ntp.org domain and provides time sync for 
local clients (two or three machines on local networks).

OpenVPN only needs to listen for clients on eth1 (outside interface) and 
eth2 (local wireless interface), while ntpd only needs to listen for 
local clients on eth0 (wired LAN) and tun0 (created by openvpnd).

My only concern is with inbound NTP packets on eth1 (outside) that ntpd 
is receiving from upstream NTP servers, and with inbound OpenVPN packets 
on the same port and same interface (openvpnd is receiving them from 

Do you think there will be any conflict between the two daemons?

If push comes to shove, I can probably run openvpnd on a TCP port, but I 
wouldn't do that if I definitely don't have to.

Florin Andrei
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