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Accepted
Vitor Mazuco
Asked: 2015-04-30 11:22:34 +0800 CST

14.04 Share Internet with 2 Network Cards

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I use an Ubuntu 14.04 32 bits

I have the following problem, I have to share Internet: 1 Internet Server (eth1) 1 Forward Internet with other network cards (this is the machine that need to configure - eth2) Pcs Customers.

The Internet comes with a network cable to the server and the other network card goes to a switch that distributes for micro clients.

Question is: how do I get the Internet a network card and distribute the other?

Thanks in advanced.

Please see my syslog 

    May  7 10:40:37 asterisk dhcpd: options subnet-mask 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 6: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options broadcast-address 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 7: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options routers 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 8: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options domain-name-servers 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 9: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options domain-name 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: Configuration file errors encountered -- exiting
    May  7 10:40:37 asterisk dhcpd: Internet Systems Consortium DHCP Server 4.2.2
    May  7 10:40:37 asterisk dhcpd: Copyright 2004-2011 Internet Systems Consortium.
    May  7 10:40:37 asterisk dhcpd: All rights reserved.
    May  7 10:40:37 asterisk dhcpd: For info, please visit         https://www.isc.org/software/dhcp/
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 5: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options subnet-mask 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 6: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options broadcast-address 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 7: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options routers 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 8: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options domain-name-servers 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: /etc/dhcp/dhcpd.conf line 9: semicolon expected.
    May  7 10:40:37 asterisk dhcpd: options domain-name 
    May  7 10:40:37 asterisk dhcpd:          ^
    May  7 10:40:37 asterisk dhcpd: Configuration file errors encountered -- exiting
    May  7 10:40:49 asterisk dhcpd: Wrote 0 leases to leases file.
    May  7 10:40:49 asterisk dhcpd: 
    May  7 10:40:49 asterisk dhcpd: No subnet declaration for eth2 (no IPv4 addresses).
    May  7 10:40:49 asterisk dhcpd: ** Ignoring requests on eth2.  If this is not what
    May  7 10:40:49 asterisk dhcpd:    you want, please write a subnet declaration
    May  7 10:40:49 asterisk dhcpd:    in your dhcpd.conf file for the network segment
    May  7 10:40:49 asterisk dhcpd:    to which interface eth2 is attached. **
    May  7 10:40:49 asterisk dhcpd: 
    May  7 10:40:49 asterisk dhcpd: 
    May  7 10:40:49 asterisk dhcpd: Not configured to listen on any interfaces!
14.04

1 Answers

  1. Best Answer

    The first thing to do is do enable IP forwarding. This is done either by using

    echo "1" > /proc/sys/net/ipv4/ip_forward

    Then, we will add a rule telling to forward the traffic

    iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT

    and finally, we ask IPtables to masquerade

    iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

    Edit 1

    Install 

    sudo apt-get install isc-dhcp-server

    configure

    sudo nano -w /etc/dhcp/dhcpd.conf

    # Sample /etc/dhcpd.conf
# (add your comments here) 
default-lease-time 600;
max-lease-time 7200;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option routers 192.168.1.254;
option domain-name-servers 192.168.1.1, 192.168.1.2;
option domain-name "mydomain.example";

subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.10 192.168.1.100;
range 192.168.1.150 192.168.1.200;
}

    restart service

    sudo service isc-dhcp-server restart
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