Re: Multiple NICS on same subnet
- From: ibuprofin@xxxxxxxxxxxxxxxxxxxxxx (Moe Trin)
- Date: Wed, 15 Mar 2006 13:59:21 -0600
On 14 Mar 2006, in the Usenet newsgroup comp.os.linux.networking, in article
<1142370559.063621.306260@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
andrew.bell.ia@xxxxxxxxx wrote:
I'm trying to understand the behavior of a configuration where I have
multiple NICs on the same subnet. (I know, its wrong, I'm just trying
to understand.)
Simple version - routing issue. The kernel will use the last NIC
configured when two routes lead to the same place.
Here's the configuration:
eth0 : 172.16.11.4
eth1: 129.143.4.5
eth2: 129.143.4.6
If you are grabbing IP addresses out of your a.. to munge your own addresses,
please use 192.0.2.x which is the famous "example.com" network. See RFC3330.
129.143.0.0 is the Academic Network of the German state of Baden-Wuerttemberg,
and 129.143.4.5 is a real live host.
eth2 is not cabled. eth0 and eth1 are cabled.
For fun and games, unplug the cable from eth1, and plug it into eth2.
When you ping the address of eth2 (129.143.4.6), you get a response.
If you look at the arp entry on the machine that originated the ping
for 129.143.4.6, you get the MAC of eth0, which isn't even on the same
logical network. No proxy ARP is turned on.
The kernel knows the IP addresses. It is responding to a valid request.
It's sending it out the hose that leads to the destination. Because there
are two, it assumes that you made an initial mistake, and really meant to
use the second bit of data you provided. If you want to get around this,
see the Adv-Routing-HOWTO.
Old guy
.
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