Frustrating network issue

[Michael O'Keefe]

John Oliver wrote:
> 
> On a machine I set up to be a firewall... Red Hat 6.2, patched, 2.2.19
> kernel, two NICs.  Worked fine with a single interface up and running at
> home and work.  When I took it to the colo room, though, it didn't.
> After swapping cabled between interfaces, monkeying with the ifcfg-ethX
> files, etc. I finally noticed that netstat -rn showed a device for the
> default gateway as well as an address.  Even though eth0 was configured
> to be 216.120.58.10/29, the default gw 216.120.58.9 was on eth1  I
> couldn't find where that would be set, so I swapped interfaces again.
> Still didn't work.  While troubleshooting, I found that after I pinged
> the interface on the box from the Catalyst, it started working!  Of
> course, it didn't *stay* working.  I figured that might be a NIC issue
> (the cards were 3Com 3C900s, old 10 Mb only guys).  So I bought a couple
> of NetGear FA311s (couldn't get any drivers that came with the kernel to
> work, but the drivers on the floppy worked like a charm, at least to
> bring the interfaces up), and had the same problem, except now even
> pinging from the Catalyst doesn't bring it up.  ifconfig always shows
> both interfaces running happily.  Everything that I've looked at seems
> OK.  But trying to ping anything that isn't local gets "Destination host
> unreachable".  GRRRRR!  What am I missing? :-)

Check your arp tables too.
If ping works, and then won't rework, it can be becoz the arp tables have been
routinely flushed, and it can't get the MAC address to respond the next time
around.

As for where it the default GW being set, I'd run the ifup script with
"#!/bin/sh -x"
and follow it thru till you see it. Watch out for running extra scripts, you'll
have to alter them too to get the full picture of whats going where.


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