We have a very interesting problem. The network is configured in this way:

• internet is connected to Trendnet switch TS

• DHCP server at 192.168.0.1 running on Ubuntu (S) is connected to internet switch

• DNS is also configured on 192.168.0.1 on S

• D-Link Wi-Fi boosters are connected to switch TS

• PCs use D-Link PCI-E Wi-Fi cards to get access to network

• PCs have both Ubuntu and Windows 7

There are about 40 PCs.

When PC is booted to Ubuntu it easily gets access to internet. But when it's booted to Windows 7, it gets a valid IP-address, but doesn't get access to internet. The address, mask, DNS, GW-address are totally the same as when it's booted under Ubuntu. The S is reacheble and pingable. Sometimes when we are lucky the PC gets access to Internet, but after rebooting it can lose it. When PC under Windows has access, it has totally the same settings as when it doesn't.

What can be done?

UPDATE I shared a dropbox with 2 captures of traffic. Ping.pcap is a capture of pinging 8.8.8.8. And google-browser.pcap is a capture of opening a google.com in a browser, both of them are in tcpdump formats and made by Wireshark on Win PC. The MAC of Win PC ends on b7:63 and IP is 192.168.0.130.

UPDATE2

This is ifconfig output from Ubuntu Server

eth0 Link encap:Ethernet HWaddr 00:1e:67:13:d5:8d
inet addr:193.200.211.74 Bcast:193.200.211.78 Mask:255.255.255.0 inet6 addr: fe80::21e:67ff:fe13:d58d/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:196284 errors:0 dropped:44 overruns:0 frame:0 TX packets:190682 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:158032255 (158.0 MB) TX bytes:156441225 (156.4 MB) Interrupt:19 Memory:c1400000-c1420000

eth0:2 Link encap:Ethernet HWaddr 00:1e:67:13:d5:8d
inet addr:192.168.0.1 Bcast:192.168.0.254 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Memory:c1400000-c1420000

eth1 Link encap:Ethernet HWaddr 00:1e:67:13:d5:8c
UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Interrupt:16 Memory:c1300000-c1320000

nslookup from Win results in DNS request timeout, nbtstat in 'not found'.