FC1 multiple ethernet interface issue

[Scot L. Harris]

On Tue, 2005-02-15 at 08:35, David Benigni wrote:
> Here is the dump from ip route list for various modes of the nics.
> 

(personally I prefer the netstat -rn output, I guess that makes me old
school.  :)  )

> eth0 up and eth1 down (normal boot):
> 10.1.0.0/16 dev eth0  scope link 
> 127.0.0.0/8 dev lo  scope link 
> default via 10.x.y.1 dev eth0 
> 

That looks fine, single interface eth0 used.

> eth0 up and eth1 up (via ifup eth1):
> 10.1.0.0/16 dev eth1  scope link 
> 10.1.0.0/16 dev eth1  proto kernel  scope link  src 10.x.y.121 
> 127.0.0.0/8 dev lo  scope link 
> default via 10.x.y.1 dev eth1 
> 

Note that the default route has switched to the eth1 interface. 
Actually it looks like all the routes are using eth1.  What happened to
eth0?  It really looks like you would have zero traffic going out over
the eth0 interface in this configuration.  You should be able to look at
the ifconfig information to get the stats in this setup.  You may see
received data but I doubt you would see much if any transmit data on
eth0.   

> eth0 up and eth1 down (via ifdown eth1):
> 127.0.0.0/8 dev lo  scope link 
> 

Would expect this result since everything was routing out the eth1
interface.  So this result makes sense and appears to be correct.

> eth0 up and eth1 down(via /etc/init.d/network restart):
> 10.1.0.0/16 dev eth0  scope link 
> 127.0.0.0/8 dev lo  scope link 
> default via 10.x.y.1 dev eth0
> 

Back to square one.

At this point the problem is not at the point you shutdown eth1.  It is
when you bring eth1 up and all your routes get pushed out that
interface.  It is that point that the system must be looking at the
addressing you are using and says the new interface has the same subnet
as the old one so all traffic can go this way.  Depending on the actual
IP address on the interface it may decide that based on the highest or
lowest IP address.  Not sure about that but that appears to be what is
happening.

So if you think this has been working with the two interfaces splitting
traffic, it probably has not.  Look at the packet stats ifconfig gives
you for each interface.  Setup some file transfers or something to each
IP address for testing.  I suspect you will see all outbound traffic on
eth1 and nothing on eth0, even for local LAN traffic.


-- 
Scot L. Harris
webid at cfl.rr.com

The typewriting machine, when played with expression, is no more
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