Possible Network Issue?
 

Hello Everyone,

I recently have been tasked with figuring out why a machine running Fedora 6 has lost internet connectivity. We have several servers on one subnet (192.168.1.x) and another set of servers in the DMZ subnet (192.168.88.x). This server is in the DMZ and has no issue pinging any of the other servers (Windows machines) within the DMZ. However, that is where the communication stops. It cannot get to the other subnet like the other machines and cannot reach the outside (internet).

One test that we tried was changing the IP to one of the machines that did work to make sure it wasn't the router. Well, it still didn't work (I'm not necessarily satisfied with that test either). The network admin really thinks it is the machine.

Here is the ifconfig
The hosts and nameservers are correct. I don't deal with linux, so I'm not really sure where to start.

I do know this only became a problem when the network was switched around. Two companies were sharing the same network, but we just recently split into two different networks. This is why I'm leaning towards the router more than anything else.

Hi, welcome to LQ!


The machine itself seems to have no problem on the physical
side of things. You may want to check whether it has host-
based firewalling enabled:

iptables -L

You mentioned that networks were "moved" ... did that machine
keep its IP, did it change?

What's its routing table?

route


Cheers,
Tink

I'll have to see if I can't find any routing tables. We have a Cisco 2811 Router and a Cisco PIX 501 Firewall.

Just issue the command 'route" on the linux box.

For the routing table just enter

You could also post the results of

route -n
cat /etc/hosts.allow (just has comments)
cat /etc/hosts.deny (just has comments as well)

Hmmm ... nothing untoward or unexpected. I'll dare say
the problem sits somewhere else. I've seen interesting
cases where e.g., one windows machine had a private subnet
on a secondary interface that happened to use the same
address range that a Linux box was on on the corporate
LAN ... took a while to find out just what was happening
and prodding the windows and network guys hard enough
to start looking ;}

I forgot to mention that the IP of the machine did not change after the split. I'll have to dig for some more information to really learn what happened with the split and how it was originally.

I decided to check the message log and found that the machine uses Avahi. My initial search showed a lot of people having issues with this. Here is the log. It has done this 3-4 times today. Not sure if it's right.

Okay, a little update. I put the server on the internal switch and it worked just fine. It could ping hosts outside and talk to all of the servers on both subnets. I switched it back and of course it's not happy. I'm not sure why the DMZ is an issue. I'm leaning more towards an issue with the switch, minus the test with switching the IP to something known to work.

Has the machine been moved to another port on the switch/router?

It sounds like an issue with the router between the two subnets, as you say. Does that have any MAC address filters in operation perhaps?

Okay, here is an update. I ended up adding the subnet 192.168.1.0 into the routing table. So now it looks like this:
I can now ping machines within that subnet. I also fixed a DNS issue. It couldn't access the outside DNS address, so changing it to the internal one fixed that. Now the problem is it still can't access the outside. The computer knows all of the hosts and IPs, it just can't get through.

It really sounds like an issue with the router or the firewall. I would get your network folk to check that there's no specific block or filter relating to that machine.

Since the server has an IP address of 192.168.88.41, don't you need a gateway entry when the target is on the 192.168.1.0 subnet?

For the first route output, the default gateway at 192.168.88.1 would be used.