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When I (and presumably my users) first start up or log in to my computer I can't get internet access until several minutes after logging in. Internet pages like serverfault.com will time out. During this time I can access internal web servers. Sometimes pinging the gateway seems to fix the problem.

I'm using Windows 7 on this machine with wifi, and the problem seems limited to the wifi network, which is on a separate vlan. The wired network does not share the problem, but I know it's not the wifi connection itself because the internal sites work.

The wifi access point is attached to a 3Com 4200 switch, with the port set for vlan 2 untagged, vlan 1 tagged. The 4200 has a fiber connection to a 3Com 4900SX fiber switch that acts almost as a router here. The fiber connection is vlan 1 untagged vlan 2 tagged at both ends. The gateway is then attached to a different 4200 (vlan 1 untagged, vlan 2 tagged) that has a similar fiber connection to the 4900SX.

vlan 2 has 192.168.8.0/22 IPs, vlan 1 has 10.1.0.0/16 IPs. The 4900SX has an interface for both vlans (10.1.1.1/192.168.8.1), as does the gateway (10.1.1.5/192.168.8.5). There is one dchp server for both vlans on the same switch as the gateway. It chooses a dhcp scope based on the interface used by the 4900sx to forward the dhcp request.

There is also a network access list on the 4900sx set to deny all vlan2 traffic to any 10.1.x.x host, with exceptions made for a few servers, including dhcp, 4900sx, and the gateway.

I think that about covers it. Any ideas on why internet access would be delayed like this?

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1 Answer 1

up vote 1 down vote accepted

This sounds like a DNS issue. More specifically, DNS queries are initially being sent to a server that is not responding (it could be down, not have a known route from the WiFi access point, an old server that no longer exists, etc.). Once the initial queries time out, another server is tried and eventually, one works. From that point, DNS queries go to the working server and you're OK. Internal sites work because you're using a different address server, such as Active Directory.

So, next time you connect to the WiFi point, check the DNS connection. A simple nslookup or dig may be enough to see which server is being tried and which one finally responds.

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This was part of it. The main thing is that my computer had the "Autodetect proxy settings" option checked, and so spent a while trying to do that after a restart. But I also found a dns error on the secondary dns server, which is for some reason occasionally preferred by wireless connections. –  Joel Coel Apr 13 '10 at 20:43

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