What did I learn in Linux today? Configured my computer through DYNDNS.ORG so I could be a real mail machine. After a bit of doing, I was receiving mail. Test messages came in fine from Yahoo and Hotmail, but Earthlink was timing out attempting to deliver mail. After tinkering and poking around Google searches, I found that there's some nasty interaction between MTU size autodiscovery and my SMC Barricade router. Apparently, Earthlink connects and sets its TCP packets to non-fragmenting. Due to a miscalculation by the MTU size discovery thingie, packets get fragmented and the inbound traffic from Earthlink stalls. It got fixed when I used ifconfig mtu 576 eth0 To make the change permanent, I edited /etc/sysconfig/network/etc/sysconfig/network-scripts/ifcfg-eth0 and added MTU=576 to the file. I'm not sure this is the optimal MTU size, but it works for now.
