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Attention: The Cisco Support Community site will be in read only mode on Dec14, 2017 from 12:01am PST to 11:30am for standard maintenance. Sorry for the inconvenience.

New Member

VPN outside problem

Hi, I am using a Cisco 837 router with a ADSL connection to the Internet. I need to use a VPN connection from my PC to a Windows 2003 VPN server over the Internet, i.e.

my PC using Windows XP connects a VPN connection via the default gateway (Cisco 837 router) -> Internet -> a site with a Nokia ADSL modem (gateway) -> the Windows 2003 VPN server (

The problem:

The VPN connection connects fine with no problems except for I cannot download anything more than 2kb (binary files, like a GIF picture) from the Windows server via the VPN connection. However, text files larger than 2kb or any size are fine. I also cannot use Remote Desktop connection to the Windows 2003 server either - it brings up a grey background window and does not go further than that. I notice the VPN connection's status Sent total is much greater than the Received bytes total.

I was using a normal Netgear ADSL router before and never have any problems. The above problem only occurs when I started using the Cisco 837 router. I think it's the MTU problem, but tried resetting and restarting with no luck.

Can any one help on this one?




Re: VPN outside problem

Hi there,

The ip tcp adjust-mss command helps prevent TCP sessions from being dropped by adjusting the MSS value of the TCP SYN packets. The ip tcp adjust-mss command is effective only for TCP connections passing through the router. In most cases, the optimum value for the max-segment-size argument is 1452 bytes.

Try this command under you Ethernet interface facing your LAN "ip tcp adjust-mss 1452"


Mohammed Mahmoud.

New Member

Re: VPN outside problem

Hi Mohammed,

Thanks for the response. Yes your answer helped in resolving the problem, i.e. I had to

1. do a "ip tcp adjust-mss 1452" against the e0 interface (just like your answer)

2. change the MTU valud to 1300 in my Windows XP LAN

The combination of the above two resolves the VPN packet problem.

While we are on this subject, is there a IOS command I can use so my VPN connection stays active after the idle time, note I think my Windows VPN icon still says connected but all tcp connections are dead?

Thank you very much!


New Member

Re: VPN outside problem

DPD (Dead Peer Detection)

CreatePlease to create content