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Re: [Openvpn-users] Incorrect tcp and udp checksums on packets from gateway to vpn clients (solved)


  • Subject: Re: [Openvpn-users] Incorrect tcp and udp checksums on packets from gateway to vpn clients (solved)
  • From: "Thibault Le Meur" <Thibault.LeMeur@xxxxxxxxxx>
  • Date: Tue, 3 Apr 2007 12:39:01 +0200
  • Importance: Normal

> 
> The problem was: The pyhsical Network Card attached to the 
> server bridge 
> was by default doing TCP checksums in hardware (Intel Gigabit 
> Ethernet 
> Adapter, em in FreeBSD Terms), to take this workload off the 
> kernel. So 
>   the packets generated by the server host had no valid TCP 
> checksum on 
> them, entered the bridge without seeing the Intel Card and 
> arrived at my 
> VPN Clients with no valid checksum on them.
> 
> "ifconfig em0 -txcsum" solved the problem. Now the kernel 
> generates the 
> checksums for all packets, they are valid when they enter the 
> bridge and 
> the communication works fine.
> 
> I'll report this issue to the FreeBSD People.
> 
>    George

Very interresting I wonder if other systems (such as linux) may suffer such
issue (or is it only a Freebsd kernel feature) ?
Maybe this should be reported to the wiki as soon as it is back online.

Regards,
Thibault


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