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Re: [Openvpn-users] OpenVPN and Comcast

  • Subject: Re: [Openvpn-users] OpenVPN and Comcast
  • From: Marco Fretz <mailinglist@xxxxxxx>
  • Date: Mon, 28 Jan 2008 14:30:23 +0100

as far as i know, openvpn is like https over the internet. so an isp may 
not be able to block openvpn packets, right?
i guess its something with ur router. linksys has got a configuration 
point "vpn pass through", but i think this  only applies to ipsec / esp 

we ve run into ssh / vpn issues with linksys and dlink modems while 
using them in router (no nat enabled) mode. this "cheap" modems are not 
forwarding the icmp messages which controls the MTU discovery correctly. 
if its an MTU issue u can try to set ur openvpn client's MTU to 
something like 1492 instead of 1500 (u have to edit this in windows 

point is: with a modem in NAT mode, the modem is ur TCP / UDP connection 
endpoint (it controls the MTU). with mode in router mode, ur client may 
be the endpoint but it can discover the MTU because the modem does not 
forward the needed icmp packets correctly.

kind regards

William Warren wrote:
> comcast does not block vpn.  See if he is running a linksys router..if 
> so check for an updated firmware.  I have run into quite a few vpn 
> issues with linksys routers lately and the latest firmware fixed it.
> Craig Sturman wrote:
>> Hi guys,
>> I’m up in Canada but our office has a salesperson out in Montana who is 
>> using Comcast as his internet provider.  I have the OpenVPN client from 
>> openvpn.se set up on his laptop and it claims to connect but will not 
>> route anything through the VPN tunnel.  I had read an older article from 
>> 2000 online that had said that Comcast blocks VPN traffic.  Is this 
>> still the case?  I have 30 other people using the VPN server with the 
>> same configuration without issue.
>> Any ideas?
>> Crag S.
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