IP/Ethernet Clue? [Δαφνη Ευτυχια Αρθουρος]

[UPDATE: Solved!]

I'm looking at a Win98 box that -- get this -- can't see any of the other machines on my LAN, but can get packets out to the Internet and back (by IP number) through my masquerading router even though it can't see the router! Ping times out between that machine and anything else on my LAN, in either direction, and traceroute only provides responses for machines past my firewall.

Additionally, tcpdump isn't showing me diddly when I ask a third machine to listen in on the ping traffic ... unless the box sending the pings is pinging the broadcast address. Does this mean that my "switch that acts like it's a mere ~~router~~ hub [grabbed the wrong noun last night, sorry] until you plug a terminal into the serial port and set a password and tell it to act like a switch" (according to the manual) is already acting like a switch without having been told that it is one? That ... makes tcpdump rather less useful as a troubleshooting tool, however more efficient it is.

Something is happening here that seems as though it sould not be possible. Perhaps two somethings. I am open to suggestions.

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Switch ports around and see what happens.
If that doesn't help, change IP addresses.

They're all coming from the same DHCP server with no MAC mappings?

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I'm not running DHCP except on the wireless hub (which only get plugged in when guests bring WiFi devices into the house). This is all static IP. All using the same netmask (I checked).

I presume you mean switch physical ports on the switch? Dunno why that hadn't occurred to me -- running downstairs to do that now.

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Running tcpdump on the same machine that's trying to ping the recalcitrant Win98 box does show ARP replies giving that computer's MAC address, but no other packets originating from it.

Switching the wires around did make the LEDs on the switch do funny things briefly (as did cycling power on the switch) but produced no changes in the output of ping and tcpdump.

But the LEDs do suggest that the switch is acting switchlike. Who told my switch it was a switch? I'd been meaning to, but I know I hadn't gotten around to it ....

We once had a problem that (as I recall) was similar to what you're describing, and it turned out to be duplicate IP addresses. In our case one machine had a fixed address and the other was getting an address via DHCP (configured such that there shouldn't have been a conflict), but they ended up matching. We now explicitly assign addresses for everything that lives on our network. You do too, it sounds like; is it possible that you've assigned the same address twice, or accidentally reset the Win98 box to use DHCP?

Nope, the Win98 machine is definitely using a static address, the only source of DHCP addresses in the house (the wireless router/hub) is unplugged, and the address (192.168.49.193) was deliberately chosen from a block of addresses I'd never used. Though I'll go telnet to every computer currently switched on Just In Case, and check ifconfig ...

Your suggestion does make a lot of sense, but I'm pretty sure that's not it.

I did check just to be sure, and that's not it.

we have a 98se box that talks tcpip across our lan just fine but windows networking refuses to get it and the XP based 'net to recognize each other.

if it weren't for the fact that its the one thing hooked up to the printer, i wouldn't have minded...

Oy. Most of my Windows machines just have to talk to the (Linux+Samba) file server, not to each other, but once in a while one needs to access another's CD-ROM.

Hmm. Maybe I should fire up another Windows box and see whether that can see this rogue 98 machine and vice-versa. (Results later after I clear a path through some Pennsic-unpacking.)

When I visited

realinterrobang and investigated the problem she'd mentioned of the machines in their house network not being able to see each other, it seemed to be a pretty weird situation. Some things could ping some other things, others not. Even after we bought a new (cheap) network switch to add extra machines in her office, the machines directly attached to that switch weren't IIRC properly able to see each other, so we figured it probably wasn't Jaygor's router box. It continued to mystify us.

After some poking about in the settings, I investigated the Win XP built-in firewall thingy. Turned out it had (by default perhaps??) "allow ICMP Ping packets" unticked (or "refuse Pings" ticked, whichever); Fixing that, it was all visible again. But, I don't think Win98 comes with a built-in firewall, and I imagine you'd have checked that sort of thing :P The situation merely reminds me of that because it had vaguely similar baffling symptoms.

Here's a question though- did you have this third machine plugged into a separate socket on the hub, or did you try using a crossover cable and plugging it directly to the misbehaving machine? I guess in the latter case you wouldn't be able to see the responses, but it'd at least give you some info. And perhaps if the machine had 2 NICs you could further configure it as a bridge, but I don't know how you'd do that and it'd probably be a big hassle if you don't already have such a machine set up :P

I would not have thought to look for firewall settings on the Win98 box itself, and I don't know of that feature being included in Win98, but I'll check a) just in case there's a detail I'd overlooked about that particular flavour of Windows, and b) in case there's already third-party personal-firewall software on it. (This is a hand-me-down just recieved by my new housemate/tenant who just finished moving in. More on that in a separate LJ entry when I get around to it.)

I don't have a crossover cable -- I should go look it up and make one just to have on hand, I guess -- but there are a whole bunch of other machines on the same hub. I set the new computer to pinging a couple of other machines, then went to my room and fired off a few Xterms and ran tcpdump from three or four machines at once to compare views, and set up pings the other direction while I was at it. That's what I was looking at when he plugged in a laptop he brought home from work (Windows also, though I'm not sure which version) and the expected traffic suddenly started showing up on my screen ... so it's not the cable and doesn't seem to be any of my machines causing the problem, but it's still mysterious.

I did think of plugging that machine and a few others into a smaller, less intelligent hub for testing. (Haven't done that yet. It's on the list of things to try.)

I could build a bridge, if I use a boot-from-CD distro of Linux in it or can cram enough of the smallish hard drives I've got into one box, but the only computer in the house that already has two Ethernet cards is the one acting as firewall/masquerading-router to talk to the antenna on the roof. The possibility of building a bridge is not ruled out, though I'd hoped to use some of the parts elsewise.

Have you tried un-plugging the switch from power? I had a similar problem of machines not seeing each other that was solved by re-booting the switch.

-m

I did try power-cycling the switch, as well as plugging all the cables into different ports on it (plenty of spare ports on it, at least currently). Made the LEDs on the switch do interesting things briefly, but no net change in behaviour. (I didn't even lose my telnet connection to panix.com!)

netmask?

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