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I have a MBP with OSX 10.7.3, from which I use a VPN connection (Cisco IPSec) to login on my company network. That in itself is not a problem.

I also have an Airport Extreme (version 7.6.1) as the backbone of my home network using ADSL to my ISP. That in itself is not a problem, either.

But the combination of the two is a major problem for everybody in the house. Especially those that play online games...

Whenever I connect to the company network, I can see the ping latency go from 20 ms to 600 ms for the ADSL leg. And is not just from my machine, but for every machine in the house. Which should mean the problem is in the Airport.

I have of cause been looking at all the usual sites, but cannot find anything similar reported before...

Without the VPN connection:

traceroute to dr.dk (195.137.194.128), 64 hops max, 52 byte packets
1  10.0.1.1  3.293 ms  0.784 ms  0.693 ms
2  nn.nn.nn.nn  19.489 ms  18.837 ms  23.681 ms
3  ...

With the VPN connection:

traceroute to dr.dk (195.137.194.128), 64 hops max, 52 byte packets
1  10.0.1.1  2.515 ms  0.553 ms  2.898 ms
2  nn.nn.nn.nn  688.489 ms  650.996 ms  690.190 ms
3  ...

So the question is: Does anybody know what is going on here? Do you know of any solution? E.g. should I downgrade the Airport software?

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  • Not cost efficient, but what you could do is to use a router that supports QoS, e.g. the ones that support dd-wrt: dd-wrt.com/wiki/index.php/Quality_of_Service. This way you could restrict the VPN bandwidth and guarantee bandwidth for the games. Another theoretical possibility would be to restrict the VPN bandwidth on the computer using the QoS of pf, one of the Lion's firewalls (it may be possible with the other, ipfw, but I don't remember if it supports QoS), but I've never done this, so can't help here.
    – lupincho
    May 15, 2012 at 7:45
  • @lupincho Thanks for the comment, but I believe the problem is not in OSX, but in Airport, as I don't see any significant increase in the traffic from OSX when enabling the VPN tunnel. My current best guess is that Airport uses CPU... For what I don't know,..
    – Tonny Madsen
    May 15, 2012 at 9:27
  • Try to enable VPN passthrough on the router, this should ease the handling of the VPN connections. The problem is that the tech specs say that it supports IPSec, PPTP, and L2TP; I am not sure if IPSec includes Cisco's flavor, so it may or may not work, but it's worth trying.
    – lupincho
    May 15, 2012 at 18:04

1 Answer 1

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It's more than likely the bandwidth used by your VPN rather than the Airport itself.

My work VPN connection with a corporate laptop used to use a lot of bandwidth, I'd notice other stuff slowing down considerably. Maintaining links to the domain servers, a VOIP client, and all of the other things installed on there used a lot of resources.

When I stopped using a corporate laptop and connected my personal laptop through a web based SSL VPN with terminal services instead, things improved a lot as it was only basically screen sharing rather than uploading and downloading actual files and data.

Unless you can set-up a proxy and monitor the usage of each device, you're not really going to find out how much bandwidth each device is using, but it's unlikely to be the VPN itself, or the Airport at fault, just the bandwidth used by what's being transferred over the VPN.

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  • I have tested your theory using tcpdump, ifconfig, etc, but as far as I can see there are no real difference. Anyway, the only application I have that needs or uses the VPN is Outlook... And if I close down that (and everything else on the machine), I still see the problem...
    – Tonny Madsen
    May 13, 2012 at 10:49

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