April 2008

Host Unreachable When Pinged

I just modded my second xbox which I got from my cousin. I gave it a static IP, put it on the network and everything looked good from the xbox side. Then I tried to FTP to it to load on some programs. Could not connect. I tried to ping and this is what I got:

icmp_seq=1 Destination Host Unreachable

Hmmm, I’d seen this before but couldn’t remember why. I searched online and found references to the routing table being configured incorrectly. I played around with mine but just ended up messing things up because it was already looking good. So then I took the same network cable and plugged it back into my first xbox which I have been using for months now. I could ping it. Plug it back into the second and it can get to the internet to download new skins for the dashboard. Hmmm what is the problem? I SSHed into one of my servers and pinged it from there successfully. Something between my laptop and the xbox.

I finally started looking at some of the settings on my wireless access point to see if something in there could possibly be messing me up. After trying some settings that I really didn’t expect to work I blindly clicked my way into the page that restricts computers on the network. I’d completely forgotten about it. See — I used to have this access point acting as my router so I had it restrict people from being on my network by MAC address. This meant that if a friend came over I would have to enter their MAC address before they could gain access. The thinking is even if they got past my wireless security code, the access point would not let them access the network because their MAC address did not match one on the list. Just one more step to throw off casual wireless snoopers.

When I moved to using IPCop for my router I just turned off the routing features of the access point and used it for a simple access point to the rest of my network from my laptop. The only thing is any computer that I want to connect to via wireless now has to be added to the MAC address filter. Since the access point is not between any of the computers on the network but mine it won’t affect any non-wireless computers (i.e. my servers) but will still affect me. Sometimes it’s the little things you forget.

I do end up learning something from these things. This time I decided to fire up tcpdump to see what was happening when my computer asked the network for the address I knew existed. It still took me a while but now I am not afraid to use tcpdump again for any future problems.

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