Red Hat 7.2

[manny_9]

question from Linux newbie.
We have server which performs two functions that we know of....email and internet gateway.

I don't know much about NAT.
What and Where would I look at, to find out out if this box is performing NAT??

Thanks In Advance
Fred

[K.C. Chan · Accepted solution]

Most likely it is using ipchains or iptables to NAT, I think it is the later; you can find out by doing iptables -L, this should list the all policy and rulesets. I would suggest you read on iptables, sorry at the moment I drawing blanks on url for iptables documents.

[Steven E. Protter]

I'm uploading a iptables configuration file that does NAT among other things.

The IP addresses have been changed to protect the innocent.

SEP

[Ragu_1]

Redhat 7.2 comes with an older Linux kernel that does not support iptables. Maybe you should start out with reading this excellent tutorial on IPTables first, http://www.linuxsecurity.com/resource_files/firewalls/IPTables-Tutorial/iptables-tutorial.html before you deploy your firewall using NAT.

[Stuart Browne]

Atually RH7.2 was the second in the series to support tables.

It uses ipchains by default, however, and thus you need to issue the following commands to make use of iptables:

service ipchains stop
rmmod ipchains
chkconfig --level 0123456 ipchains off
chkconfig --level 2345 iptables on
service iptables start

This will do most of the legwork for you.

After that , 'iptables -t nat' is your friend. DNAT, SNAT, REDIRECTS, or even MASQUERADE's.

[manny_9]

Thanks to everyone who responded! BIG HELP!!

I now have somewhat of a clue.
When i did iptables -L i found out that iptables is really doing NAT.
Is there anything else that would work in conjunction with iptables? What/where should i check to find out exactly what this box is doing. We are in the process of building a new one.

[manny_9]

Anyone???

[Alexander Chuzhoy]

Hi. Running "netstat" with it various options will show on what ports your server is listening-what services are running.
Iptables is widely used for the following:
* build internet firewalls based on stateless and stateful packet filtering
* use NAT and masquerading for sharing internet access where you don't have enough addresses
*use NAT for implementing transparent proxies
* aid the tc+iproute2 system used to build sophisticated QoS routers
* do further packet manipulation (mangling) like altering the TOS field of the IP header


For more information:
www.iptables.org

[Alexander Chuzhoy]

Forgot to mention:
service --status-all |grep running 2> /dev/zero
will output all running sevrices
Best regards

[Jerome Henry]

Another valuable tool for nating and controling in/out transit is squid.
http://www.squid-cache.org

hth

J