Wed May 5 18:16:57 GMT 2004 So what's new with you?
I had a call this morning from an SME customer who said his server was down. Well, sort of down: he said it worked "sometimes".
I was able to ssh to the server, so obviously it wasn't really down. Yet he said his network had no internet access. A quick check of "ifconfig -a" showed that eth0 (his LAN card) wasn't up. Attempting to bring it up ("ifup eth0") generated:
Error, some other host already uses address 192.168.2.53.
Ahh, that would be a problem. So I asked if anything new had been added to the network. "Nothing", I was told.
OK, "arp -an" told me that the MAC address for this IP began with 00:30:AB. Looking that up at https://standards.ieee.org/regauth/oui/index.shtml told me that the nic was made by Delta Electronics. I looked them up on the web and told the client that these folks made tablet PC's and switches etc. No help.
Hmm.. OK, I started a ping running and asked him to start unplugging wires from his switch. Unfortunately, there were only a few systems plugged into the switch he was near; the main switch was located in their attic, with no phone nearby. None of the wires he was able to unplug stopped the ping.
Not expecting much, I tried "telnet 192.168.2.53". Son of a gun, I had a password prompt. Again not expecting success, I tried a few of their main server passwords and then tried "1234", which logged me in and gave me:
RP114 Main Menu Getting Started Advanced Management 1. General Setup 21. Filter Set Configuration 2. WAN Setup 3. LAN Setup 23. System Password 4. Internet Access Setup 24. System Maintenance Advanced Applications 11. Remote Node Setup 12. Static Routing Setup 15. SUA Server Setup 99. Exit
Hmm.. looks like a Netgear router to me. Yep, sure is. Actually, it looks suspiciously like the Netgear router that the SME server replaced a few years back. What the heck is this doing on the network? Well.. apparently they ran out of ports on the switch, and just needed a couple more, so.. yes, they plugged this in and fanned a few systems off it. Never thought about its prior use and setup. For whatever reason, they had some network problem that caused them to reboot the SME, and of course with this device hard configured and connected, the SME couldn't use the .53 address. Unplug the old router, reboot, and all was well. My guess (I didn't ask) is that it was probably the machines connected to this router that couldn't access the internet, so they rebooted the SME hoping to fix that, and that broke everything.
Moral: a router is not a switch or a hub even if it does look like one.
The really sharp readers may wonder how I could ping if eth0 wasn't up. Good question: for historical reasons, we always had an alias on this nic:
ifconfig eth0 --add alias 126.96.36.199
That gave me access to the lan even though the main address wasn't functional.
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More Articles by Tony Lawrence © 2012-06-27 Tony Lawrence
The activity of "debugging", or removing bugs from a program, ends when people get tired of doing it, not when the bugs are removed. (Datamation)