How to find IP address of ADSL modem?

by Jasmine Lognnes   Last Updated June 28, 2015 19:00 PM

Our fall back Internet connection uses a SpeedStream 4100 modem, which just broke, so I have replaced it with a new one. I need to configure it to bridge mode, but I can't even find its IP address.

According to this page is the default IP and a dhcp server should hand out IP addresses. I can't see it does that. Here is what I have done:

  • Reset it to factory defaults by holding in the reset button.
  • Connected it to my Fedora laptop with the straight RJ45 cable from the box.
  • service network restart on by laptop with is configured to use DHCP.
  • dhclient -r to ask for a new IP. Didn't work.
  • Set my IP to and netmask but still can't access from a browser.


Can anyone give me some debug ideas how to figure out how to connect to the modem, as it doesn't seam to give out a DHCP address to my laptop?

Btw. Are there any chance that I need a crossover cable?

Answers 1

Chances are high that a "tcpdump -n -i eth0" launched on your fedora box, once connected to the router, will show an ARP probe that, probably, the router will raise to check if its LAN IP address is already in use somewhere else.

This will happen shortly after the router is powered up.

As for the crossover cable, I don't think you need it, anyway you can check if ethernet link is UP simply issuing a "ethtool eth0" and reading the output.

Also note that you will see your own traffic, with tcpdump, so take care to carefully follow the output stream.

BTW: it could be possibile to heavily limit your own generated traffic, by disabling Network-Manager and force the eth0 to go "online". Anyway... this should not be necessary.

PS: Sorry to not provide links: I'm typing from my smartphone.

Damiano Verzulli
Damiano Verzulli
June 28, 2015 16:52 PM

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