[Vpn-help] Problems with a Sierra Wireless HSDPA Network Adapter

Matthew Grooms mgrooms at shrew.net
Sun Oct 18 17:40:12 CDT 2009


amnesiac at iinet.net.au wrote:
> Hi,
> 
> I'm using the ShrewSoft VPN Client 2.2.0 to connect to my employers 
> CISCO IPSEC VPN from my Vista x64 SP2 laptop.
> 
> Everything works fine when I use a wired or wifi connection, but when I 
> use my Sierra AirCard 880E 3G card I can connect and get about 20secs of 
> use.
> 
> After 20secs the tunnel remains up, but I don't have any web or Outlook 
> conectivity and PINGs stop responding.
> 
> I've got a feeling that this is due to packets being dropped, maybe 
> because the MTU is wrong? The Sierra card has the following settings on it:
> 
> BufferAdjustment = 0
> EnableWINS = 0
> IPAddress = 10.0.0.5
> IPPacketSize = 1450
> MaxMRU = 1500
> 

Have you looked at the debug level output? If you can communicate for 20 
seconds or so, I assume the ESP or NAT-T/ESP packets are making it to 
the gateway. However, cell carriers do really strange things with their 
data networks sometimes.

I would start be decreasing the Virtual adapter MTU to a very low size ( 
512 bytes ). If that works, increase it until it stops working reliably 
to determine a good setting for your carrier.

If that doesn't work, try disabling NAT-T support. For some reason this 
causes issues with UDP traffic with some carriers. I have always assumed 
this was UDP packet size related but maybe they are doing something even 
more scary to evaluate the traffic.

Lastly, the debug level output may be showing a DPD timeout for some 
reason. If so, you can try disabling DPD on your client and see if this 
has a positive effect.

Hope this helps,

-Matthew



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