LinuxSecurity.com
Share your story
The central voice for Linux and Open Source security news
Home News Topics Advisories HOWTOs Features Newsletters About Register

Welcome!
Sign up!
EnGarde Community
Login
Polls
What is the most important Linux security technology?
 
Advisories
Community
Linux Events
Linux User Groups
Link to Us
Security Center
Book Reviews
Security Dictionary
Security Tips
SELinux
White Papers
Featured Blogs
All About Linux
DanWalsh LiveJournal
Securitydistro
Latest Newsletters
Linux Advisory Watch: August 29th, 2014
Linux Security Week: August 25th, 2014
Subscribe
LinuxSecurity Newsletters
E-mail:
Choose Lists:
About our Newsletters
RSS Feeds
Get the LinuxSecurity news you want faster with RSS
Powered By

  
( MULTIPLE IPs - DMZ segments) - I have several EXTERNAL IP addresses that I want to PORTFW to several internal machines. How do I do this?

7.32. ( MULTIPLE IPs - DMZ segments) - I have several EXTERNAL IP addresses that I want to PORTFW to several internal machines. How do I do this?

Though technically possible, DON'T do this with IP MASQ. There are far better solutions for this network design.

MASQ is a 1:Many NAT setup which is the incorrect tool to perform what you are looking for. You are looking for is either Many:Many NAT solution or a Briding setup.

NOTE: For users out there who are thinking about enabling multiple IP addresses on one internal NIC using "IP Alias" and then just PORTFWeding ALL of those ports (0-65535), and and finally use IPROUTE2 to maintain the proper source/destination IP pairs. This has been done SUCCESSFULLY on 2.0.x kernels and less successfully on 2.2.x kernels. Regardless of success, that isn't the proper way to do it, it's a total HACK, and it is not a supported MASQ configuration. Please, give IPTABLES on the 2.4.x kernels a serious look or to a much lesser extent, Section 7.30 IPROUTE2 look for 2.2.x kernels.

Anyway, for forwarding external IP address to internal hosts, you basically have three possibilites:

  • 1. Route the external IPs 
    
       (This does NOT involve IPMASQ at all but requires special WAN addressing 
        and routing setup from your ISP):
    
        Internet -- Some public WAN -- Linux -- DMZ segment
                       IP address      Server     PUBLIC IPs
                                         |
                                         +------ Internal net
                                                  private IPs

  • 2. 1:1 NAT 
    
       (Most easily done via IPTABLES or with IPCHAINS and IPROUTE2 but still 
        some protocols cannot deal with NAT)
    
        Internet -- Linux -- DMZ segment
                    Server     Private IPs natted to 1:1 PUBLIC IPs
                       |
                       +------ Internal net
                                private IPs

  • 3. Bridging or ProxyARP:  
    
       The Bridging method is one of the more popular methods that many commercial 
       firewalls do and it's very slick.  Alternatively, you can use the ProxyARP 
       method which works well without some of the complications (or benefits of
       bridging).  With both solutions, all public IPs can transparently flow 
       through the Linux server to the DMZ but via firewall inspection.
    
        Internet -- Linux -- DMZ segment
                    Server     PUBLIC IPs
                      |
                      +------ Internal net
                               private IPs

Each of these solutions have pros and cons

Item #1: If you're lucky enough to have an ISP that will set this up for you (pretty rare), all you need to do is use basic 'route' commands to get this running. This is the most rebust solution and doesn't require any form of IPMASQ or NAT to work.

Item #2: 1:1 NAT isn't covered in this HOWTO yet but if you need a hand, just email me and I'll give you a hand.

Item #3: ProxyARP is pretty strait forward but only works in specific situations and only works with Ethernet networks. Bridging is more powerful but will probably require the re-compiling of the kernel and some advanced configuration. Ultimately, neither of these solutions are IPMASQ anymore and thus I can't help you set them up. Fortunately, there are other HOWTOs out there that cover this topic:

NOTE: If you have a bridged DSL or Cablemodem connection (not PPPoE), things are a little more difficult because your setup isn't routed. No worries though, check out the Bridge+Firewall Mini HOWTO and the Bridge+Firewall+DSL Mini HOWTO. These HOWTOs will teach you how to get your Linux box to support multiple IP addresses on a single interface!

    
Partner

 

Latest Features
Peter Smith Releases Linux Network Security Online
Securing a Linux Web Server
Password guessing with Medusa 2.0
Password guessing as an attack vector
Squid and Digest Authentication
Squid and Basic Authentication
Demystifying the Chinese Hacking Industry: Earning 6 Million a Night
Free Online security course (LearnSIA) - A Call for Help
What You Need to Know About Linux Rootkits
Review: A Practical Guide to Fedora and Red Hat Enterprise Linux - Fifth Edition
Yesterday's Edition
Partner Sponsor

Community | HOWTOs | Blogs | Features | Book Reviews | Networking
 Security Projects |  Latest News |  Newsletters |  SELinux |  Privacy |  Home
 Hardening |   About Us |   Advertise |   Legal Notice |   RSS |   Guardian Digital
(c)Copyright 2014 Guardian Digital, Inc. All rights reserved.