Ubuntu Networking problem

Nils Kassube kassube at gmx.net
Sat Oct 18 18:20:28 UTC 2008

sreenivas desamsetti wrote:
> I am using HP Proliant DL 145 G2 with AMD Opteron server.
> It is giving internet problem after changing the mother board.
> This server is in lan. Whenever I used to connect I cannot get dirctly
> I have to change the back side port. then it gets connected.
> For example today I connected to port1, after restartig/starting the
> machine I have to change the port then its gets connected to
> internet/lan.

So if I understand it right, your connector for port1 is sometimes at the 
interface eth2 and sometimes at eth3?

> When I check if config it is showing
> eth2      Link encap:Ethernet  HWaddr 00:17:A4:FF:77:B5
>           inet addr:  Bcast: 
> eth3      Link encap:Ethernet  HWaddr 00:17:A4:FF:77:B4
>           inet addr:  Bcast: 

That looks suspicious. Both interfaces have the same IP address. Do you 
use a manual setup for your interfaces or do you get your configuration 
via DHCP?

> But when I see the /etc/iftab file it shows
> eth0 mac 00:13:21:b5:31:6f arp 1
> eth1 mac 00:13:21:b5:31:70 arp 1

I don't see a contradiction here. Probably eth0 and eth1 were used for the 
previous main board. As the new mac addresses are not included in this 
file the association of LAN port and interface isn't fixed and may change 
at each boot. You could write the mac addresses of your new main board to 
this file and then the old configuration should work again even if you 
have a static setup for eth0 / eth1.

OTOH, /etc/iftab isn't used by recent Ubuntu versions. Therefore please 
tell us which ubuntu version you are using. Ubuntu 8.04 (and I think 7.04 
and 7.10 as well) use /etc/udev/rules.d/70-persistent-net.rules for the 
association of mac addresses and interface name.


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