WinXP - Having trouble sharing internet with 3G USB modem via ICS
- by Carlos Nunez
all! I've been banging my head against a wall with this issue for a few days now and am hoping someone can help out.
I recently signed up for T-Mobile's webConnect 3G/4G service to replace the faltering (and slow) DSL connection in my apartment. The goal was to put the SIM in one of my old phones and use its built-in WLAN tethering feature to share Internet out to rest of my computers. I quickly found out that webConnect-provisioned SIMs do not work with regular smartphones, so I was forced to either buy a 4G-compatible router or tether one of my old laptops to my wireless router and share out that way. I chose the latter, and it's sharpening my inner masochistic self by the day.
Here's the setup: GSM USB modem (via hub), ICS host - 10/100 Mbps Ethernet NIC, ICS "guest" - WAN port of my SMC WGBR14N wireless router in bridged mode (i.e. wireless access point). Ideally, this would make my laptop the DHCP server and internet gateway with the WAP giving everyone wireless coverage. I can browse internet on the host laptop fine.
However, when clients try to connect, they get a DHCP-assigned IP from the laptop and are able to use the Internet for a few minutes before completely dying. After that happens, they are able to re-associate with the WAP and get IP addresses, but are unable to use Internet or resolve IP addresses until the laptop and router are restarted. If they do get access, it's very, very slow. After running Wireshark on the host machine, it turns out that this is because every TCP connection keeps getting RST. DNS seems to work.
I would normally think the firewall is the culprit here, but when it drops packets, it drops them completely. The fact that TCP connections are being ACK'ed by the destination rules that out. Of course, none of the event Log isn't saying anything about what's going on. I also tried disabling power management on the NIC, since that's caused problems in the past; that didn't help either. I finally disabled receive-side scaling as per a Microsoft KB (that applied to Windows Server 2003, SP2) to no avail. I'm thinking of trying it with a different NIC (will be tough; don't have a spare Ethernet NIC around for the laptop), but I'm getting the impression that this simply doesn't work.
Can anyone please advise? I apologise for the length of this post; all contributions are much appreciated!
-Carlos.
