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Re: [Openvpn-users] Very strange replay problem


  • Subject: Re: [Openvpn-users] Very strange replay problem
  • From: "James Yonan" <jim@xxxxxxxxx>
  • Date: Wed, 2 Jun 2004 14:25:13 -0000

Jon Nelson <jnelson-openvpn@xxxxxxxxxxx> said:

> 
> I'm running 1.6.0-2 (Debian) and 1.6.0-0.1 (build myself for SuSE).
> 
> I had a very strange problem about a week ago.
> 
> I did some hardware futzing on the SuSE machine and rebooted it.
> When it came up, none of the network stuff worked.
> A few reboots later, I determined the cause to be OpenVPN - it was
> seemingly working fine on the SuSE machine, but on the Debian machine
> the OpenVPN daemon was complaining thusly:
> 
> Wed May 26 23:36:41 2004 151[0]: Authenticate/Decrypt packet error: bad
> packet ID (may be a replay): [ #92688 /
> time = (1085632475) Wed May 26 23:34:35 2004 ] -- see the man page entry
> for --no-replay and --replay-window for more info
> 
> Over and over again.  Over the course of 45 minutes, the SuSE box
> couldn't initiate a connection to the Debian box (the SuSE box is the
> client, forgot to mention that).
> 
> The configs are very simple. I'm using a pre-shared static key, tun,
> float (stupid NAT'ing router between the two boxes) and not much else.
> As it turns out, I had to remove the state file (replay-persist file)
> and restart the Debian's daemon.  I tried restarting both daemons
> several times with no luck.
> 
> Initially, the client side had a 'ping 5' option, but I moved that up to
> 'ping 15' and then later 'ping 30' just in case the the pings were
> causing some strange interaction with the replay file sliding window.
> 
> What went wrong?

No, the pings should not affect the replay window.

Did the problem clear up when you deleted the replay state file?

Aside from actual replay attacks, there are a few things that can cause replay
false alarms:

* Packet duplication occurring in the network link because of badly configured
routers.

* System clock backtracking.  If you start openvpn to connect to a peer, stop
it, move your system clock backward in time, and then restart openvpn, you
will get errors like this.

* High latency links such as satellite links which can cause a greater amount
of packet reordering and therefore needs a larger sliding window size.

James


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