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RE: [K12OSN] eth0 and eth1

Stephen, from all the response I’ve seen tonight, some of which give very detailed explanations of how the kernel assigns logical names to physical devices and so on, I thought I would give you my input based on my personal experiences with both Ubuntu/Edubuntu and K12LTSP.

From what I have been able to understand, both use the same default assignments; eth0 is for the thin client network, and eth1 is for the internet side. Edubuntu default install assigns eth0 to static ip address, however, eth1 I setup to get an ip address via dhcp, see /etc/network/interfaces file. As to which interface gets assigned eth0 or eth1, I think several of the responses addressed that fairly well. Although I personally found that integrated Ethernet interfaces are generally assigned to eth0, and the first PCI installed Ethernet interface is assigned to eth1. However, if you have nic failure in Ubuntu/Edubuntu, and replace that interface with another, then the network manager will assign a new logical name like eth2 or eth3. Then you can have a lot of fun reconfiguring the interface name to the one that originally failed.

One of the quirks with the default Edubuntu setup is that the /etc/default/dhcp3-server doesn’t have eth0 nor eth1 assigned, but uses the default INTERFACES="”, which I assume means either none or all, since no default setting is configured even though the LTSP default config sets up dhcp on eth0, and set eth1 to get ip addressing via dhcp.

Another Edubuntu default configuration quirk is in the /etc/ltsp/dhcpd.conf file where the default settings for eth0 (remember that Edubuntu sets this as the default thin client interface) are all set to instead of the statically assigned default ip address automatically assigned when you install it, see /etc/network/interfaces file.

It’s these kinds of quirks that make me not feel too comfortable with Edubuntu.  If there was one clear document that explained how it is supposed to work and gave examples for the various config settings, then I’m sure it would be a nice platform. But, there are a lot of documents out there that are not complete, have conflicting information, or missing bits and pieces, and yes I have googled and been though every piece of information I could find in forums and online documents.  If the developers would get involved with a couple actual deployments and walked through the process several times, I believe they would find areas that need tweaking and others that need to be put back into “let’s rethink this one” category.

I wish you luck, as I had little to none with Edubuntu.



From: Stephen Crampton [mailto:SteveSings gmail com]
Sent: Sunday, September 07, 2008 10:43 AM
To: k12osn redhat com
Subject: [K12OSN] eth0 and eth1


Could someone please explain how an LTSP system decides how to use eth0 and eth1?

For instance, if I pull up firefox and type in cnn.com, over which interface does my request go out?

Which interface is serving DHCP and TFTP requests?

/etc/ltsp/dhcpd.conf doesn't seem to provide the answer.  The DHCP script under /etc/init.d refers to a variable $INTERFACES, but I cannot figure out where that variable is initialized.

I'm assuming that, in the default case, firefox sends requests over both interfaces, but dhcpd only uses eth0.  But how do I determine whether this is true or not for my system?

I'm using Edubuntu 8.04 again, because none of the K12LTSP install discs recognize my SATA hard drives (I tried 5SEL, 6SEL, and a beta live version).

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