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Thread: IP Tables help?

  1. #1
    Join Date
    Mar 2013
    Beans
    31

    IP Tables help?

    Hey, I understand I'm new, and I apologize if this is posted in the wrong section, but I've currently got Ubuntu Server running. My question is about iptables. Obviously, there are a lot of people trying to teach me through google searches about what it is, and how to go about doing what I need. While I'm spending time learning all the nitty gritty details I would like some help. I am CCNA parts 1&2 completed, so I am not exactly a noob when it comes to all this.

    I have a Ubuntu server with 3 ethernet connections that is going to be used as a router, and I am having problems getting it to work correctly. I followed a guide for setting up a NAT router that had me install a DHCP server, after I had set up a bridge between eth1 and eth2, and that's working how I was hoping, I think. It gives out IPs with the correct information, but I have no internet access on the client machines. So, I tried another iptables configuration that is supposedly more secure in /etc/rc.local, but it doesn't give me internet access while cutting out all SSH accessibility. I'll post my file contents, and hope someone can/will help me.

    /etc/rc.local

    Code:
    #!/bin/sh -e
    #
    # rc.local
    #
    # This script is executed at the end of each multiuser runlevel.
    # Make sure that the script will "exit 0" on success or any other
    # value on error.
    #
    # In order to enable or disable this script just change the execution
    # bits.
    #
    # By default this script does nothing.
    
    # Delete all previously existing rules
    #/sbin/iptables -F
    #/sbin/iptables -t nat -F
    #/sbin/iptables -t mangle -F
    #/sbin/iptables -X
    
    # Always accept loopback traffic
    #/sbin/iptables -A INPUT -i lo -j ACCEPT
    
    # Allow established connections
    #/sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
    #/sbin/iptables -A FORWARD -i eth0 -o br0 -m state --state ESTABLISHED,RELATED $
    
    # ALLOW INCOMING OPEN PORTS TO THE SERVER FROM OUTSIDE HERE
    
    
    # Allow outgoing connections from the LAN side
    #/sbin/iptables -A FORWARD -i br0 -o eth0 -j ACCEPT
    
    # Masquerade
    #/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
    
    # Reject any non-established connections from the WAN
    #/sbin/iptables -A INPUT -m state --state NEW -i eth0 -j REJECT
    #/sbin/iptables -A FORWARD -i eth0 -o br0 -j REJECT
    
    #OLD FORWARDING BITS
    /sbin/iptables -P FORWARD ACCEPT
    /sbin/iptables --table nat -A POSTROUTING -o eth0 -j MASQUERADE
    exit 0
    /etc/network/interfaces

    Code:
    # This file describes the network interfaces available on your system
    # and how to activate them. For more information, see interfaces(5).
    
    # The loopback network interface
    auto lo
    iface lo inet loopback
    
    # The primary network interface
    auto eth0
    iface eth0 inet dhcp
    
    iface eth1 inet manual
    
    iface eth2 inet manual
    
    auto br0
    iface br0 inet static
    address 192.168.0.1
    netmask 255.255.255.0
    network 192.168.0.0
    broadcast 192.168.0.255
    bridge_ports eth1 eth2
    /etc/dhcp/dhcpd.conf

    Code:
    #
    # Sample configuration file for ISC dhcpd for Debian
    #
    # Attention: If /etc/ltsp/dhcpd.conf exists, that will be used as
    # configuration file instead of this file.
    #
    #
    
    # The ddns-updates-style parameter controls whether or not the server will
    # attempt to do a DNS update when a lease is confirmed. We default to the
    # behavior of the version 2 packages ('none', since DHCP v2 didn't
    # have support for DDNS.)
    ddns-update-style none;
    
    # option definitions common to all supported networks...
    option domain-name "google.com";
    option domain-name-servers 8.8.8.8, 8.8.4.4;
    
    default-lease-time 3600;
    max-lease-time 7200;
    
    # If this DHCP server is the official DHCP server for the local
    # network, the authoritative directive should be uncommented.
    authoritative;
    
    # Use this to send dhcp log messages to a different log file (you also
    # have to hack syslog.conf to complete the redirection).
    log-facility local7;
    
    # No service will be given on this subnet, but declaring it helps the
    # DHCP server to understand the network topology.
    
    #subnet 10.152.187.0 netmask 255.255.255.0 {
    #}
    
    # This is a very basic subnet declaration.
    
    subnet 192.168.0.0 netmask 255.255.255.0 {
      range 192.168.0.100 192.168.0.150;
      option subnet-mask 255.255.255.0;
      option broadcast-address 192.168.0.255;
      option routers 192.168.0.1;
    }
    
    # This declaration allows BOOTP clients to get dynamic addresses,
    # which we don't really recommend.
    
    #subnet 10.254.239.32 netmask 255.255.255.224 {
    #  range dynamic-bootp 10.254.239.40 10.254.239.60;
    #  option broadcast-address 10.254.239.31;
    #  option routers rtr-239-32-1.example.org;
    #}
    
    # A slightly different configuration for an internal subnet.
    #subnet 10.5.5.0 netmask 255.255.255.224 {
    #  range 10.5.5.26 10.5.5.30;
    #  option domain-name-servers ns1.internal.example.org;
    #  option domain-name "internal.example.org";
    #  option routers 10.5.5.1;
    #  option broadcast-address 10.5.5.31;
    #  default-lease-time 600;
    #  max-lease-time 7200;
    #}
    
    # Hosts which require special configuration options can be listed in
    # host statements.   If no address is specified, the address will be
    # allocated dynamically (if possible), but the host-specific information
    # will still come from the host declaration.
    
    #host passacaglia {
    #  hardware ethernet 0:0:c0:5d:bd:95;
    #  filename "vmunix.passacaglia";
    #  server-name "toccata.fugue.com";
    #}
    
    # Fixed IP addresses can also be specified for hosts.   These addresses
    # should not also be listed as being available for dynamic assignment.
    # Hosts for which fixed IP addresses have been specified can boot using
    # BOOTP or DHCP.   Hosts for which no fixed address is specified can only
    # be booted with DHCP, unless there is an address range on the subnet
    # to which a BOOTP client is connected which has the dynamic-bootp flag
    # set.
    #host fantasia {
    #  hardware ethernet 08:00:07:26:c0:a5;
    #  fixed-address fantasia.fugue.com;
    #}
    
    # You can declare a class of clients and then do address allocation
    # based on that.   The example below shows a case where all clients
    # in a certain class get addresses on the 10.17.224/24 subnet, and all
    # other clients get addresses on the 10.0.29/24 subnet.

  2. #2
    Join Date
    Jun 2005
    Location
    Toronto, Canada
    Beans
    Hidden!
    Distro
    Xubuntu 14.04 Trusty Tahr

    Re: IP Tables help?

    Duplicate threads merged.

    Please do not create duplicate threads - it dilutes community effort.

  3. #3
    Join Date
    Mar 2013
    Beans
    31

    Re: IP Tables help?

    Sorry, I wasn't sure where to place it. Can you remove the duplicate then?

  4. #4
    Join Date
    Feb 2011
    Location
    Coquitlam, B.C. Canada
    Beans
    1,403
    Distro
    Ubuntu 12.04 Precise Pangolin

    Re: IP Tables help?

    Most of your iptables rules are actually commented out. iptables rule sets are difficult to read at the best of times, so I'm not sure, but I think if you just uncomment the rules things might work as expected.
    Any follow-up information on your issue would be appreciated. Please have the courtesy to report back.

  5. #5
    Join Date
    Mar 2013
    Beans
    31

    Re: IP Tables help?

    Quote Originally Posted by Doug S View Post
    Most of your iptables rules are actually commented out. iptables rule sets are difficult to read at the best of times, so I'm not sure, but I think if you just uncomment the rules things might work as expected.
    I've tried commenting the currently uncommented ones, and uncommenting those other ones. I gain no internet access from the DHCP clients, and can't SSH into the server with the ones that are currently commented. I'm at a loss.

  6. #6
    Join Date
    Oct 2009
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    Hidden!
    Distro
    Ubuntu 12.04 Precise Pangolin

    Re: IP Tables help?

    Why not use iptables-restore instead of writing up a bash script to apply the rules?
    Come to #ubuntuforums! We have cookies! | Basic Ubuntu Security Guide

    Tomorrow's an illusion and yesterday's a dream, today is a solution...

  7. #7
    Join Date
    Mar 2013
    Beans
    31

    Re: IP Tables help?

    I was told to put those in the rc.local file by the guide I was initially following. I'm not sure of another way to save the iptable configurations, what else is there?

  8. #8
    Join Date
    Oct 2009
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    Distro
    Ubuntu 12.04 Precise Pangolin

    Re: IP Tables help?

    iptables-save and iptables-restore

    If I am testing firewall rules, I will use iptables-apply so I don't locked myself out of the machine.

    Check this out:
    http://bodhizazen.net/Tutorials/iptables
    Come to #ubuntuforums! We have cookies! | Basic Ubuntu Security Guide

    Tomorrow's an illusion and yesterday's a dream, today is a solution...

  9. #9
    Join Date
    Mar 2013
    Beans
    31

    Re: IP Tables help?

    With as many iptable commands as I had written it seems such a pain if I wind up losing that all in the process. Is there a way to save them into a file, and to not add them into a non-visible running portion that can be run on command? I also couldn't figure out if it was checking the file each time for what to do, and the commands had to be in order (I assumed the file's rules were loaded into RAM on boot).

    Oh, wow, that is the most well written piece on all this I've found. Thank you so much. I'll be looking into that for the next hour or so. LOL Is there any light on my specific situation you'd be willing to pull your hair out for, and share with me?

  10. #10
    Join Date
    Oct 2009
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    Distro
    Ubuntu 12.04 Precise Pangolin

    Re: IP Tables help?

    I don't know why you are bridging eth1 and eth2.

    If you are going to be using your box as a "router" this might help:
    http://itsecureadmin.com/wiki/index....using_IPTables
    Come to #ubuntuforums! We have cookies! | Basic Ubuntu Security Guide

    Tomorrow's an illusion and yesterday's a dream, today is a solution...

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