I have been intermittently trying to set up a filtering bridge for a
small network using OBSD 3.6. Installation goes well, but none of the
internal machines can access the outside world or get an IP address from
the router. The network configuration is ISP>cable modem>router/DHCP
server providing non-routable addresses>bridge>switch>internal boxes.

I read in one manual that a crossover cable was needed to connect the
bridge to the internal machine. Is that true? If so, does the
crossover cable go between the switch and the bridge or between the
switch and each internal machine?

Thanks,

G

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In comp.unix.bsd.openbsd.misc, Kernel Mustard dared to utter,
> The network configuration is ISP>cable modem>router/DHCP
> server providing non-routable addresses>bridge>switch>internal boxes.
>
> I read in one manual that a crossover cable was needed to connect the
> bridge to the internal machine. Is that true? If so, does the
> crossover cable go between the switch and the bridge or between the
> switch and each internal machine?

Yes it's true. Let me demonstrate this by showing the pin-out of a
regular 568B patch cable first.

1 = orange-white
2 = orange
3 = green-white
4 = blue
5 = blue-white
6 = green
7 = brown-white
8 = brown

1 2 3 4 5 6 7 8
| | | | | | | |
- ----------------------
||||||||
- ----------------------
| | | | | | | |
1 2 3 4 5 6 7 8

So you notice in a patch cable (a "regular" CAT-5 cable you might say)
that everything passes straight through. When you connect this to a
switch or hub, the switch or hub has receivers aligned somewhat like
this.

3 6 1 4 5 2 7 8

Basically the orange pair from the cable connects to the green pair on
the switch and vice-versa. Since you're using two NICs with no switch
between them, you need a cross-over cable made like this.

1 2 3 4 5 6 7 8
| | | | | | | |
- ----------------------
||||||||
- ----------------------
| | | | | | | |
3 6 1 4 5 2 7 8

With a cross-over cable, the cable itself connects the orange pair of
one NIC to the green pair of the other, and vice-versa. Make sense?
You need to connect the cross-over cable between the bridge and the
router so the connections look like this.

1 2 3 4 5 6 7 8
| | | | | | | |
1 2 3 4 5 6 7 8
| | | | | | | |
- ----------------------
||||||||
- ----------------------
| | | | | | | |
3 6 1 4 5 2 7 8
| | | | | | | |
1 2 3 4 5 6 7 8

If you've got it configured thusly and there are no problems with the
cable, you can be pretty sure the physical layer is alright, and you've
got some sort of software configuration problem.

- --
It is better to hear the rebuke of the wise,
Than for a man to hear the song of fools.
Ecclesiastes 7:5
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you don't need a cross-over if you are using a switch. a cross-over is
to connect two machines directly.