When is "ifconfig <interface> up" necessary?

Hi all

The problem: In our LAN we run Debian 5.0 i386 (5.0.4 with upgrade)
"Standard System" freshly installed as a guest within VMware
Workstation 7.0 on Win XP. The simulated network cards are "bridged"
to the corres. physical interfaces - there are two. We configure one
with "dhclient eth0". All of them get an address but only some of
them are active, I mean, ping & Co, works. In the others we must
execute "ifconfig eth0 up" for it to work.

Why is this necessary? And why in some of the machines?

CU
Arun

Arun Vidarjee <(E-Mail Removed)> wrote:
> The problem: In our LAN we run Debian 5.0 i386 (5.0.4 with upgrade)
> "Standard System" freshly installed as a guest within VMware
> Workstation 7.0 on Win XP. The simulated network cards are "bridged"
> to the corres. physical interfaces - there are two. We configure one
> with "dhclient eth0". All of them get an address but only some of
> them are active, I mean, ping & Co, works. In the others we must
> execute "ifconfig eth0 up" for it to work.

Are you using "Network Manager" or /etc/network/interfaces directly? If
the latter, what's the difference between one that works as expected
and one that doesn't?

Chris

Hi

On 22.11.2010 18:22, Chris Davies wrote:
> Arun Vidarjee<(E-Mail Removed)> wrote:
>> The problem: In our LAN we run Debian 5.0 i386 (5.0.4 with upgrade)
>> "Standard System" freshly installed as a guest within VMware
>> Workstation 7.0 on Win XP. The simulated network cards are "bridged"
>> to the corres. physical interfaces - there are two. We configure one
>> with "dhclient eth0". All of them get an address but only some of
>> them are active, I mean, ping& Co, works. In the others we must
>> execute "ifconfig eth0 up" for it to work.
>
> Are you using "Network Manager" or /etc/network/interfaces directly? If
> the latter, what's the difference between one that works as expected
> and one that doesn't?

No fancy Network Managers. The VM (guest) is pure Debian 5.0 "Standard
System". All out people work with the bord tools. For example,
- fresh boot, log in as root
# dhclient eth0
(output of dhclient with an IP address from the pool 192.168.1.X)

on some computers
# ping 192.168.1.1
(no output)
# ifconfig eth0 up
# ping 192.168.1.1
(ping working perfectly)

on other computers (without "ifconfig eth0 up")
# ping 192.168.1.1
(ping working perfectly)

Why are they different? Why some need ifconfig ... up?

All hosts are identical (Windows XP) all guests as well (fresh
Debian 5.0).

Arun

Arun Vidarjee <(E-Mail Removed)> wrote:
> No fancy Network Managers. The VM (guest) is pure Debian 5.0 "Standard
> System".

I've not got one of those anymore. What's in your /etc/network/interfaces?
Chris

Hi Chris

On 23.11.2010 10:54, Chris Davies wrote:
> Arun Vidarjee<(E-Mail Removed)> wrote:
>> No fancy Network Managers. The VM (guest) is pure Debian 5.0 "Standard
>> System".
>
> I've not got one of those anymore. What's in your /etc/network/interfaces?

Nothing which has eth0 or eth1 in it. I can't start the VM right now,
because I write this from my Linux laptop which has no VMware, but
I'm sure I've left /etc/network/interfaces exactly as the installation
script left it. I installed Debian in an identical stand-alone PC,
no network connection.

I think the file has
auto lo
lo inet 127.0.0.1
or something very similar.

This on purpose. The whole thing is an exercise. I want the
participants to configure interfaces manually. They are supposed
to do
# dhclient eth0
(because it is connected to a LAN which has a DHCP-Sever)
# ifconfig eth1 static.ip.addr netmask the.net.mask
(they connect this side together to a switch)

Do you suggest, having
auto eth0
auto eth1
would have eliminated the need for "ifconfig interface up" command?

What is the explanation?

regards
Arun

Arun Vidarjee <(E-Mail Removed)> wrote:
> Do you suggest, having
> auto eth0
> auto eth1
> would have eliminated the need for "ifconfig interface up" command?

Yes. Or allow-hotplug eth0 // allow-hotplug eth1.

"auto" tells the system to bring up the interface automatically.
"allow-hotplug" allows udev to bring up the interface if it exists (*not*
when the cable is attached). My preference is "auto", since I don't have
hotpluggable interfaces.

Chris