Network Card Strangeness

Network Card Strangeness

Post by Jonathan A » Sun, 24 Oct 2004 00:26:56


I have four network cards in an FC2 machine. This machine is supposed
to act as a system router between different segments of a LAN, some of
which is Windows, most of which is Linux, some 10baseT and some 100baseT:

eth0: NC100 Network Everywhere Fast Ethernet 10/100 -- a PCI card
Manuf: Linksys Driver: tulip

eth1: NC100 Network Everywhere Fast Ethernet 10/100 -- a PCI card
Manuf: Linksys Driver: tulip

eth2: NC100 Network Everywhere Fast Ethernet 10/100 -- a PCI card
Manuf: Linksys Driver: tulip

eth3: 3c940 10/100/1000Base-T [Marvell] -- on motherboard
Manuf: 3Com Corp Driver: sk98lin

In the System Services->Network control panel, all three devices appear
and can be activated. They then stay active until reboot or network
restart, but I can't seem to get a 'ping' to work through eth1 or eth2
even if I use 'route' to make them the default. 'ifconfig' shows them
all present with their (different or same, it doesn't seem to make any
difference) IP addresses and 'route' shows almost the correct segment
routing, except that they all have on them which I don't

Regardless of the active/inactive state in the control panel, on boot or
network restart, only eth0 and eth3 are started. Why is this ?

I am trying to get to:

eth0: host IP, route: default
eth1: host IP, route: only
eth2: host IP, route: only
eth3: host IP, route: only

Any ideas how can I get there ?


Network Card Strangeness

Post by Jean-David » Sun, 24 Oct 2004 03:15:38

Are you sure you have it like this? I do not believe you should give the
same IP address to more than one NIC. I have two NICs (on the motherboard)
of one of my computers, and gave them different addresses; e.g.,

eth0: host IP
eth1: host IP

Then machine could talk to it on one net and machines and could talk to it on the other.

.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey
^^-^^ 14:10:00 up 7 days, 1:41, 3 users, load average: 4.24, 4.33, 4.28


Network Card Strangeness

Post by Juha Laih » Sun, 24 Oct 2004 04:34:38

Jean-David Beyer < XXXX@XXXXX.COM > said:


Good point from Jean-David;
If you're making a router
- each adapter should have an IP address suitable for the network to
which the adapter is connected
- all networks connected to a single router should have distinct
network addresses (i.e. what is left when you do a "bitwise and"
with a host address on the network and the netmask of the network)

If, on the other hand, you insist having the same IP address on all
interfaces (and thus, implicitly, having parts of the same IP network
behind each of the interfaces), then you need to read up on bridging
(so, you're building a multiport bridge -essentially a switch- instead
of a router).
Wolf a.k.a. Juha Laiho Espoo, Finland
(GC 3.0) GIT d- s+: a C++ ULSH++++$ P++@ L+++ E- W+$@ N++ !K w !O !M V
PS(+) PE Y+ PGP(+) t- 5 !X R !tv b+ !DI D G e+ h---- r+++ y++++
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Network Card Strangeness

Post by Nico Kadel » Sun, 24 Oct 2004 22:43:11

There are some fascinating ways to do things like this on routers, but in
general it's a bad idea.

Network Card Strangeness

Post by Jonathan A » Wed, 27 Oct 2004 00:37:21

Yes - that's exactly what I'm trying to do - bridge between two different
speed parts of the same network. One arm is only 10BaseT, the other arm
is 100BaseT, and doesn't need to see any of the network traffic that doesn't
actually concern it.

So, if I set all the IP addresses and netmasks to be the same, how do I
do the forwarding/bridging between the eth0 and eth1 ?


Network Card Strangeness

Post by ibuprofi » Thu, 28 Oct 2004 11:20:59

[compton ~]$ grep Bridge HOWTOs
-rw-rw-r-- 1 gferg ldp 29687 May 21 2002 Bridge
-rw-rw-r-- 1 gferg ldp 21151 Apr 26 2001 Bridge+Firewall
-rw-rw-r-- 1 gferg ldp 20465 Nov 9 2000 Bridge+Firewall+DSL
-rw-rw-r-- 1 gferg ldp 21956 Nov 13 2002
[compton ~]$

What you want is a transparent bridge - they've been around for years.
Alternatively, use a 10/100 Switch with the appropriate number of ports.

Old guy