2 networking cards, all data sent through one

[boltronics]

Hi all. I've been trying various GNU/Linux distributions for ages, but now I think I'll be hooked on Gentoo for life.

Anyway, I've never networked 2 cards before. Neither card is a module (a monolithic kernel) and both appear to be configured correctly in /etc/conf.d/net:

iface_eth0="192.168.1.15 broadcast 192.168.1.255 netmask 255.255.255.0"
iface_eth1="192.168.1.50 broadcast 192.168.1.255 netmask 255.255.255.0"
gateway="eth0/192.168.1.10"
gateway="eth1/192.168.1.10"

ifconfig seems to confirm that both cards are correctly installed and configured. I can ping both 192.168.1.15 and 192.168.1.50 from any machine on the local network, and all appears to work. Something at this stage caught my eye however: the hub indicates that only one card is actually being used. Pulling the one cable confirms it: I cannot access the machine at all (from another computer). Why can't it use the other card?

Is this because the Linux kernel knows that it's the same network reachable via both cards (and hence ignores the second)? Or have I misconfigured something?

Thanks.
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[cram]

You would need to recompile your kernel with support for ECMP as well as some configuration with iproute2. I've never done this but I imagine it might be a bit difficult if you've never worked iproute before.

btw, I understand using two cards on a gateway machine if you have access to two internet connections but I'm curious why you're doing this on an internal box, do you really need to double your bandwidth within the lan?
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Good point Chewie.

[boltronics]

OK. Thanks a lot for your help - I'll look into it.

As for two cards (and not being a gateway), it's actually only a temporary testing setup. It's going to be a webserver. One will be the public connection, and another will be to a local network for backup/fallover purposes.
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[cram]

[boltronics]

Ok. Thanks anyway. I don't have access to two different networks simultaneoulsy to test, however I'm just trying to verify that the second card will function as expected when server goes live.

Come on guys Somebody out there must think it's weird that when I pull one cable, I loose my connection to both cards?
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[Carlos]

[krusty_ar]

if you wasnt to be absolutely sure that both connections work you can do three things

1) delete teh route from the card that is getting all the trffic, that way the kernel will choose the other (ok, not to realistic)

2) check the ping man, there's a way to force the traffic trough one specific interface (probably a specific ip too). if it's going to be a webserver, set httpd to listen on one ip and then the other

3) from the other machines, ping both ip's of that box (not too sure what failures can be determined with this one)

you can think of more probably
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[boltronics]

Carlos, thanks for the netstat command info - very helpful. Armed with this information, I'm sure I wont have any problems when we go live.

Krusty_ar:
1. Tried that. The card works fine when that is done (confirming what Carlos said).
2. I tried ping with the -I switch (interestingly left out of the manual).
Even though I I use the commands:
ping -I 192.168.1.15 192.168.1.10
ping -I 192.168.1.50 192.168.1.10
they both work through the same card. It still looks at the Kernel IP routing table.
3. Pinging both IPs from other computers still use the same network interface, too.

Thanks all - very useful advice.
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