[techtalk] Weird network interface behaviour

[Magni Onsoien]

Jeff Dike:
> magnio at pvv.ntnu.no said:
> > Then we upgraded the kernel to 2.2.14, and the behaviour changed: now
> > it suddenly started to announce the name/IP on the last virtual
> > interface on eth0 as its name, fex. when being used for irc or when
> > NFS-mounting directories.
> 
> There was a complaint about this on the kernel list a few days ago.  According 
> to Andi Kleen: "tough", although Andi did write a little utility to give your 
> interfaces symbolic names so you can refer to them by those names rather than 
> whatever the kernel decides to call them this week.

Unfortunately this is a different problem from mine. This person problems
with old eth0 becoming eth1 and vice versa, but I have not experiences
this problem (not even when changing from 2.2 -> 2.4). (At least not
that I am aware of, I'll test it a bit.)

Here is an example of my problem: Say that my box impala.domain.no has IP
10.1.2.3. This resolves to the correct hostname and all is good. I
configure eth0 to have this hostname and I want to refer to impala with
this name and adress usually.

Then impala is turned into a web hotel. I then add several virtual
interfaces on eth0 (we can, just for the simplicity, assume that there
is only one NIC).
eth0:1 webmail.domain.no 10.1.2.4
eth0:2 abc.example.com 10.1.2.5
eth0:3 animal.ntnu.no 10.1.2.6

etc.
(I just made up IPs here now, in reality the boxes have other IPs. That
is NOT the problem.)

But I still want to have impala as the main name of the box, and I want
to export my disks etc to impala.domain.no. But the problem with 2.2.x,
x>6 (at least), is that impala will now announce animal.ntnu.no as it's
name in public, so if I ssh out from it to another server it looks like
I come from ntnu.no instead of domain.no (which is bad because I may use
AllowHosts in my sshd_config), and if I try to mount an NFS share it has
to be available to animal.ntnu.no in order to work.

So with this kind of use, this is quite a big problem - I want to be
able to add an "infinite" number of virtual interfaces and I don't want
to have to change my configfiles for ssh, NFS etc all the time. I guess
I can just say that eth0:1000 or something is impala.domain.no, but
honestly, that's no solution even if it works.

I'll do some testing today (if I have time), because I now have a box
with three different NICs (and drivers); the behaviour may vary from
driver to driver. (But I know the problem is there for at least the 
eepro100 and 3c509 drivers.) I think it's a bit strange that so few
people have experienced any problems, so I guess it may be only some
cards with this problem or there is a configuration error in my
kernel...


Magni :)
-- 
sash is very good for you.