networking weirdness

[cellio]

Ever since the power surge (and resulting replacement of Linksys box and one other hub), we have been noticing sporadic weirdness on our network. We use DHCP to hand out IP addresses (doesn't everybody?). The Linksys box is configured (by default, if I recall correctly) to start handing out addresses at 192.168.1.100. The Linksys itself is 192.168.1.1. As best I recall, these are the same settings we used successfully on its predecessor for close to three years.

So now, every now and then, it will hand out the address 192.168.1.2. And that unlucky machine will be able to see the LAN but not the internet. Rebooting usually does not fix it, but creative sequences of reboots of all machines and power-cycling of the modem and Linksys usually do the trick.

We cannot find any common factor when this happens. Sometimes it just does.

Tonight, when I found myself the unwilling owner of 192.168.1.2, I decided to try an experiment: I gave myself a fixed IP address without changing anything at the Linksys end. I guessed that I should use 192.168.1.1 for the gateway and name service, rather than the "real" ones; after all, the Linksys box is supposed to resolve the interface issues between the local machines and the network, right?

This worked perfectly. In fact, in a rare Windows moment, I didn't even have to reboot!

I assume that as the other machines encounter the wayward 192.168.1.2 we'll make this adjustment on them, too, until nobody's using DHCP any more. Then we'll forget about this until some unlucky house guest wants to plug his laptop into the network. :-)

I feel like this is an ugly hack. I have not solved the real problem. But at this point I think I'm going to stop looking for it.

Because there is a strict quota on hardware happiness, I found that the 4-port hub we had lying around is really only a 2-port hub. (One is "uplink", which seems to be magic and does not work with anything I tried to plug into it, and one is just dead.) So I can't get rid of the cables strung across the floor just yet.

Comments

[geekosaur]

"Uplink" is usually wired crossover (1<->3, 2<->6).

[cellio]

Yeah, I've heard this mysterious word "crossover". Wish I knew what it means. :-)

Some hub or linksys documentation somewhere along the line implied that the "uplink" slot is for chaining hubs. We have three hubs in the house right not (geography problems, not technical necessity). The linksys box is one, a second is upstairs, and a third -- the new one -- is across the room from the linksys box so I can temporarily plug two machines into a KVM switch.

There is no special labelling on the linksys box. The left-most slot is filled with the connection to the DSL modem; the right-most slot is empty. One of the random middle ones leads to the hub upstairs, and that connection works fine. I haven't checked to see what slot it's plugged into on the upstairs hub.

So I ran a cable from another random middle slot to the new hub. When I plugged it into the "uplink" slot the other machines on that hub couldn't see the internet. When I plugged it into another slot they could.

There is also a toggle labelled "normal/uplink", but it appears to have no effect on any of this. I don't have the documentation for this particular hub; I think it was scrounged somewhere.

Oh well; the need that is motivating the use of this hub is temporary anyway.

[ironangel]

Yeah, I've heard this mysterious word "crossover". Wish I knew what it means. :-)

it means that the wires inside the port are wired backwards from normal, and in order to connect it to another (non uplink) port, you need a crossover cable - an ethernet cable that is wired normally on one end and reversed on the other.

:)

[cellio]

Ah! (Light dawns.) Thanks! Dani knows how to make those. In fact, I wouldn't be surprised if he's done it by accident. :-)

[geekosaur]

I guess I used too much shorthand: a crossover cable has pins 1 and 3 swapped and pins 2 and 6 swapped. :)

Also, quite a few hubs I've seen provide normal and crossover versions of one port, the latter for chaining hubs, and woe be to whoever tries to connect both at the same time....

[cellio]

Thanks for the clarification.

The weird thing, to me, is that I would expect that if you get the crossover stuff wrong, then the result would be that machines on that hub can't see stuff on the other end of that crossover connection. So, for example, machines on my 4-port hub wouldn't be able to see the internet (which is connected to the next hub over), but would be able to see each other. But the machines can't see each other if I use that connection for anything.

(I suppose it's possible that the connection is simply bad. It lights up, though -- which the known-bad one does not.)

[geekosaur]

Nope. Hubs are dumb; use a non-crossover cable and you will in fact confuse all the ports, because internally they're all connected. Now if it were a switch, you'd be right --- but most switches are also smart enough to tell you when things are miswired, and some will even automatically sense the need for an MDI port instead of an MDI-X and change over automatically.