[lug] ethernet duplex options, mysteries

Mr Viggy LittleViggy at alum.manhattan.edu
Fri Aug 2 14:57:33 MDT 2002

Of course you can ping and, with no cables attached. 
What's happening is that in the TCP/IP stack for each card is the IP 
addy for those cards.  The ping command is actually being responded to 
from the stack, *not* the network itself.  If you need to ping test the 
cards, you're going to need a third machine somewhere else on the 
network that you can ping.  You can ping your local machine anytime; 
even if it's not connected to the network.  What this proves is that the 
TCP/IP stack for that interface is up and running.

As for having both interfaces on the same network, I'm not sure what 
that will acomplish (other than maybe twice as fast network speeds).  I 
don't think you can remove that default route; your system is probably 
seeing that both cards are on the same network, and using the last card 
it finds as the default (pure speculation on my part).

As for mystery #2, you got me...  All my cards are 100/full...


D. Stimits wrote:
> I have 2 NIC's in my Linux machine, not yet set up for bridging (so far 
> they are ordinary ethernet devices without any non-ordinary options). Of 
> the two NICs, one is a Linksys LNE100TX card using only RJ45 connectors. 
> The other card is an NE2000 clone, only capable of 10 Mbps. The NE2000 
> has both coaxial and RJ45 connectors available, but only the RJ45 is 
> being used. Both NICs are PCI. Bootup messages seem correct, and 
> ifconfig shows both eth0 and eth1 correctly, currently with ip addresses 
> and for eth0 and eth1, respectively. I think eth1 
> belongs to the Linksys 100 Mbps card, and the 10 Mbps NE2000 clone is 
> eth0 (I'm not positive). Loaded kernel net card modules (2.4.18-4 Redhat 
> kernel) are:
>  tulip
>  n2k-pci
>  8390
> (it looks like both n2k-pci and 8390 belong to the NE2000 clone, and 
> tulip only to the Linksys)
> I connect to a switch that has indicator lights for speed and half/full 
> duplex, one each for every cable slot. To aid diagnostics, one of the 
> switch lights blinks over the particular cables when that cable has 
> traffic. Mystery: I can ping or, and they actually 
> ping without loss. No switch lights blink, so the traffic is not 
> touching the switch (I don't have a 2nd machine on this switch to test 
> with yet, the indicator lights are it...and due to not enough cables, I 
> can only connect eth0 or eth1 to the switch at any given moment). The 
> route command indicates there is a default route (interface 
> eth1), and route del refuses to allow me to remove it (unless I shut off 
> eth1 interface...I don't want to do that, I want eth1 up, but no default 
> route). I can use a route add default and have a 2nd default route to 
> eth0, but I cannot remove the eth1 default route without turning eth1 
> off entirely.
> Regardless of which ethernet card has a default route, neither card 
> actually has anything connected, other than the switch (and I have tried 
> this with neither card connected to the switch, or a single card, but 
> never both cards at once), so how is it possible that I can successfully 
> ping both and, even with the cables removed? I do NOT 
> have any /etc/hosts entries that would supply a or 
> address alias...there is nothing that would cause 10.0.0.x to look like 
> a local loopback entry, and ifconfig confirms that loopback is only 
> [perhaps Linux has evolved and now understands Star Trek 
> subspace communications, or else I have accidentally created the first 
> Linux quantum tunneling driver :P ]
> Mystery 2. The clone NE2000 card is supposed to be able to operate in 
> full duplex if RJ45 is used, but it is currently half duplex. I have 
> been trying to find out how to force it to try full duplex. I do not 
> mind it being a 10 Mbps card, but I do want full duplex out of it 
> (presumably this would offer slightly lower latency, even if the cable 
> modem can't go at the card speed). Is there a way to force full duplex, 
> aside from a kernel boot parameter? And if a kernel parameter is 
> required, I cannot seem to find the right one for NE2K pci clones. I 
> have also tried adding in the /etc/modules.conf entry for the NE2000 
> module "duplex=full", this has no effect. If needed, I will dump the 
> NE2k clone, and replace it, but it seems like a waste since the cable 
> modem will never need more than what the NE2k can handle. Can anyone 
> tell me how to force a PCI NE2000 clone to run full duplex? I don't mind 
> if it crashes, at least I'll know, and I can replace the card if that is 
> the case.
> D. Stimits, stimits AT idcomm.com
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