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Old 10-16-2003, 05:16 PM   #1
Registered: Aug 2003
Location: El Dorado, AR, USA
Distribution: Debian, Mandrake, Suse, Knoppix, Lindows
Posts: 33

Rep: Reputation: 15
Problem with Redhat 9 and IP Aliasing and IP Forwarding

I am a Computer Network Instructor (yes I do know Linux pretty well, but still having trouble)

Network is setup like this:

1 Clark Connect Firewall connected to a switch on subnet

Redhat 9 file server connected to same switch, also on subnet

connection from switch to two other switches and there are 7 subnets configured between the two switches: 192.168.10,20,30,40,50,60,100.0 (I did this because I am trying to demonstrate a larger enterprise network in my classroom environment

I have the 7 class subnets configured as IP Aliases on the Redhat server, as eth0:1 to eth0:7 and the main eth0 is configured on the subnet.

The problem is I cannot ping from any of the lower subnets farther than the server, they will not get to the firewall, and the server will ping the firewall but will not get outside of it. I have configured one machine in class to use the firewall as a gateway and that works fine, I can get out to the rest of campus and the internet. I tried to locate the configuration file where IP Forwading is turned on in Redhat, but the only file I can find is /etc/sysctl.conf, when I turn on IPForward here it has no effect. I know I am just missing something simple, but cannot figure out what, so I am posting it here and seeing if the Linux Community can help me. I do appreciate any help I can get. Thanks.

Scott Adams
Computer Networking Instructor
SEARK College
Pine Bluff Arkansas
Old 10-18-2003, 07:43 AM   #2
Registered: Mar 2003
Location: Scotland
Distribution: Slackware, RedHat, Debian
Posts: 12,047

Rep: Reputation: 66
Welcome to LQ.

/etc/sysctl.conf should have:
net.ipv4.ip_forward = 1
net.ipv4.ip_dynaddr = 1

You will also need to set up a masquerading rule using iptables to forward the requests on.


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