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I have an ADSL modem. I have one desktop and one laptop connected to the modem. The desktop has xp and the laptop has windows 7. Both the machines are able to get the ip through DHCP. The problem is my desktop is able to connect to internet but my laptop can not. I can't ping from my laptop to the modem. I checked with wireshark. ARP is working properly and even 3 way handshake is also successful. My machine is getting syn/ack from the modem. Means the layer 4 protocol is working. This time when I tried to ping the modem again. No reply. I can't understand. Layer 4 protocol is working but layer 3 is not. How it is possible? Can somebody explain me what the problem can be? Thanks in advance.(I was able to connect to internet from my laptop before. Since last 4 days, this problem has arised.)

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migrated from serverfault.com Oct 25 '10 at 19:04

This question came from our site for professional system and network administrators.

    
Give us your full network path from the modem to both computers, including all routers, switches, cables and their pinouts and the computers and their IP addresses. If layer 3 is working, don't worry about layer 4, check layer 1 and 2 first. How are you even verifying that TCP is working? –  MaQleod Oct 26 '10 at 5:45

1 Answer 1

  • Is your laptop really getting an IP via DHCP, or is your laptop's IP one that begins with 169.254.X.X. if this is the case, your laptop is not getting an IP via DHCP, but rather assigning an APIPA one to itself. You might be using a crossover cable where you need a straight through.

  • Many ADSL modems have just one ethernet port and a USB port. If you are trying to share internet by connecting one PC to the ethernet port and another to the USB port it will not work. You need to get an Ethernet switch to add more ports.

  • Tell us the source and destination addresses you've used in your testing.

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