Home network troubleshooting for using cable modem, laptop/pc and wireless router

Jephe Wu - http://linuxtechres.blogspot.com

Environment: home cable modem network in Singapore (ISP: Starhub), Mortolona cable modem, Linksys WRT54 ver2.2 wireless router and laptop/pc
Objective: home network issue troubleshooting for accessing Internet.

Network diagram:
cable wall socket->cable modem->network cable RJ45 -> Linksys wireless router -> laptop/pc connected through physical cable or wireless access point
Issue: able to connect to wireless router through physical cable or access point and get IP address from wireless router itself, but cannot access Internet.

Troubleshooting steps:
1. basic troubleshooting to find out the problem
Everything seems okay between  laptop and wireless router, laptop can get IP address and can access wireless router admin page at http://192.168.1.1(default linksys wireless router IP address).

2. check admin page router status page
Find out router itself cannot get WAN IP address actually.


3. Check cable modem itself (sequence is important, otherwise, you might not be able to get WAN IP address)
Disconnect network cable between cable modem and wireless router.
Connect a dell laptop to cable modem by RJ45 cable.
Shutdown both cable modem and laptop first (totally power down)
Power on the cable modem to wait for the first 4 lights become solid green (if standby light is on after that, please press the button on the top of the modem)
Now power on the laptop and wait for the PC/Activitity light is on
Check if the laptop is getting WAN ip address from ISP through DHCP (ipconfig /all)

In my case, the cable modem is okay and laptop is getting WAN IP and is able to access Internet.

4. Solve the problem of wireless router
Try above steps in point 3, shutdown power for both cable modem and wireless router, connect cable modem and wireless router through RJ45 network cable, power on cable modem first then wireless router later, check admin page, this time, the wireless router can get WAN IP address but client laptop/pc are still not able to access Internet(try to ping 8.8.8.8, cannot).

Try to check Linksys website to upgrade firmware if it's not the latest one. It's already latest in my case.
Use wireless admin page at http://192.168.1.1 to reset to factory default settings.
Then modify the settings such as wireless router admin password, SSID and WPA2 personal/AES password.

Optional - to disable Block Anonymous Internet Requests  — This setting prevents the router from being able to be pinged or otherwise connected to on the external interface, unless you have defined a port-forwarding filter. This should be enabled, but keep in mind that not being able to ping the router can make it more difficult to troubleshoot.

Disable UPnP under Administration page.

With above setting is disabled, then configure port forwarding settings.

5. References
http://www.ciscopress.com/articles/article.asp?p=598649&seqNum=5