I had a customer today who brought in a laptop and wanted to switch over to Ubuntu linux. I always try to go the extra mile for people who want to convert to Linux. After installing Ubuntu 10.04 LTS, I rebooted and to my dismay the wired (eth0) interface was not working. I always run into wireless problems with Linux but its pretty rare that a wired interface doesn’t work. Below I show the fairly simple fix.
TCtrace is like a brother to itrace and traceroute but it uses TCP SYN packets to trace. This makes it possible for you to trace through firewalls if you know one TCP service that is allowed to pass from the outside. Once again its a very simple tool like the last few I have reviewed and it has one specific function.
The next tool up for review in the information gathering section is tcptraceroute. tcptraceroute is a traceroute implementation using TCP packets. The more traditional traceroute sends out either UDP or ICMP ECHO packets with a TTL of one, and increments the TTL until the destination has been reached. By printing the gateways that generate ICMP time exceeded messages along the way, it is able to determine the path packets are taking to reach the destination. The problem is that with the widespread use of firewalls on the modern Internet, many of the packets that traceroute sends out end up being filtered, making it impossible to completely trace the path to the destination. However, in many cases, these firewalls will permit inbound TCP packets to specific ports that hosts sitting behind the firewall are listening for connections on. By sending out TCP SYN packets instead of UDP or ICMP ECHO packets, tcptraceroute is able to bypass the most common firewall filters.