Arcane IP Conflict to Watch Out For

Posted: January 20, 2010 in Troubleshoot

Every once in a while, someone flags the NCP Help Desk with an arcane VPN connection question. Earlier this week, we came across a blog post by Merrick Chaffer on EMC Consulting Blogs, offering advice on just such an issue, and we thought we’d share it. Merrick decided to solve the problem on his own (Help Desk certainly would have ‘cracked this nut’ in an hour or so!).  

After spending a couple of weeks worrying that I’d have to be plugged directly into my router to connect to my work VPN network, with my Dell D830 Latitude laptop and Windows 7 64 bit, I finally chanced upon the solution. It turned out to be a device manager setting and potentially a setting in the BIOS on my D830 dell latitude (bios revision A14).

Follow the following steps if you are suffering the same issue yourself…

1. Changed the MTU setting on the VPN device…

2. Changed a setting in the bios, which dictated that the wifi connection should be turned off when another connection is available (i.e. LAN or 3G).

UPDATE: 23:15 15 January 2010: Actually I’ve just discovered the real route of my problems. Turns out that if my router (3com office connect adsl wireless 11g firewall router), assigns an ip address that is in use by one of the virtual server LAN IP addresses, on either wireless connection or LAN connection, then the VPN software fails to connect.

What actually happened was when I plugged another router into my firewall router, I got assigned 192.168.1.3 to my laptop wireless card, which wasn’t one of the entries in the virtual servers table, and that’s when it started working.

So if you have trouble connecting, double-check if you have conflicting IP addresses, or, drop us a line – help@ncp-e.com or @VPNHaus

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