Δαφνη Ευτυχια Αρθουρος

In case anyone was wondering about what turned out to be wrong with that Windows 98 machine that could get through my LAN to the Internet but couldn't see any machines on my LAN, and how it was finally made to work, here is (as Paul Harvey would say) The Rest Of The Story.

First, a little more strangeness: For one thing, there were two entries in that computer's routing table exactly identical to each other, for the subnet for my LAN. And I could not delete any routes at all except for the default route (0.0.0.0). And at one point, using 'tcpdump' on a different computer, I saw an ARP packet that said:

arp who-has 192.168.49.193 tell 192.168.49.193

So the situation was that

1. Since it couldn't "see" my nameserver, it couldn't look up any addresses by name (so all other tests described here were done by typing IP addresses in by hand),
2. It didn't respond to pings from other machines,
3. Pings from it to other local machines timed out and never even appeared in 'tcpdump' listings on any other machine,
4. Even though it could not see 192.168.55.254, my gateway, it could still somehow send packets through the gateway onto the Internet and get responses back -- even establish telnet and FTP sessions.

When I finally learned that the Windows equivalent of the 'ifconfig' command is 'ipconfig', I saw that the computer thought it had two Ethernet interfaces. I looked at the back of the machine for another Ethernet connector and didn't find any, just as I expected (since I'd watched silmaril and Breno transplant the Ethernet card into the machine in the first place, and load Ethernet drivers off a Windows installation CD, the day the computer was brought into the house). Eventually it dawned on me that although it didn't have a second Ethernet interface, it could well have a second TCP/IP interface ... so I clicked the "Properties" button of the Dial-Up Networking interface in the Networking control panel, got the expected message in a pop-up window telling me that settings for dial-up connections were usually particular to, and handled by, the specific dial-up connections themselves, not applied generally to the interface at this level, clicked through to look at the configuration anyhow, and saw an IP address and netmask already set up there matching the settings for the Ethernet adaptor.

Reasoning that the reason it couldn't see local machines was because it was trying to use the unconnected modem, but somehow knew to send gatewayed packets through the Ethernet card, I clicked the DHCP button in the Control Panel:Networking:Dial-Up:Properties window, and rebooted the machine.

Even the boot sequence looked different. And it asked for silmaril's Windows Networking password (which it hadn't done before) and popped up an IM login box (which it hadn't done before) ... and suddenly everything that I had expected to Just Work when we plugged the machine in to begin with ... Just Worked. DNS worked. Pinging local machines by name or by number worked. Telnetting to my Linux machines worked. Once I sorted out Samba administration details that I'd forgotten how to do because I haven't needed to tweak my Samba settings in a long time, mapping a networked drive to a directory on my file server worked. Everything Just Worked.

So: problem solved, mystery solved, clues acquired. The one remaining question is: will I remember this if I ever bump into this set of symptoms again in the distant future?

*Whew*