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First of all, here is my /etc/network/interfaces

auto lo 
iface lo inet loopback 

auto eth0 
iface eth0 inet static 
address 10.10.4.142 
netmask 255.255.255.0 
gateway 10.10.4.1 

auto eth1 
iface eth1 inet static 
address 10.10.4.138 
netmask 255.255.255.0 
gateway 10.10.4.1 

At boot time, both eth1 and eth0 are reachable and usable.

I shut down my eth1 interface with

ifdown eth1

My ifconfig does not show my eth1 interface.

But, when i try to ping 10.10.4.138 (the ip address attached to my eth1), it pings!

I don't think that should be the normal behavior. If so, can you explain me why? Why can we ping an "ifdowned" interface?

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If you ifdown eth1 AND you physically unplug the cable to eth1, can you still ping 10.10.4.138 ? –  Steven Monday Jan 21 '11 at 16:06
    
No, already tested –  ohe Jan 21 '11 at 16:19
    
Can you throw up the output of "route -n" as well? –  Niall Donegan Jan 24 '11 at 10:20
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1 Answer

up vote 1 down vote accepted

It looks like both interfaces are connected to the same subnet and same broadcast domain. Are you sure there isn't another device on the network that also has the ip of 10.10.4.138? Maybe when you drop eth1, it's then pinging 10.10.4.138 via eth0?

I would try running Wireshark/tshark on the two interfaces (separately) when eth1 is down, and seeing where the packets are going.

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In fact, and after verification. Both interfaces are connected to the same ... hardware interface. I think that this is the explanation of this behavior. –  ohe Jan 24 '11 at 10:10
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