Difference between revisions of "Internet sharing"

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[[it:Internet Share]]
 
[[it:Internet Share]]
 
[[ru:Internet Share]]
 
[[ru:Internet Share]]
==Preface==
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This article explains how to share the internet connection from one machine to other(s).
Let's assume you have an Internet connection and you want to share it. There are two main ways to do that.
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<pre>
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==Requirements==
  Internet                          pc1
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* The machine acting as server should have an additional network device
1. ----> |router| ---> |switch| --->-<
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* That network device should be connected to the machines that are going to receive internet access. They can be one or more machines. To be able to share internet to several machines a [[Wikipedia:Network switch|switch]] is required. If you are sharing to only one machine, a [[Wikipedia:Ethernet crossover cable|crossover cable]] is sufficient
                                      pc2 ..etc
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{{Note|If one of the two computers has a gigabit ethernet card, a crossover cable is not necessary and a regular ethernet cable should be enough}}
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  Internet
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2. ------> |pc1 (router)| --> pc2..etc
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</pre>
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==Instructions==
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==Configuration==
I'll explain the second way (it is easier and requires one less machine).
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Using [[Udev#Setting static device names]], name the network device connected to the other computer(s) as '''''net0''''' and the network device connected to the internet as '''''internet0'''''.
<ol>
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===Static IP address===
<li>Install a second network card to the first PC.</li>
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Assign an static IPv4 address to the interface connected to the other machines. The first 3 bytes of this address cannot be exactly the same as those of another interface.
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{{bc|
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# ip link set up dev net0
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# ip addr add 139.96.30.100/24 dev net0 # arbitrary address
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}}
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To have your static ip assigned at boot, you can use [[netctl]].
  
<li>Connect the two PCs using an ethernet cable or a [[Wikipedia:Network switch|switch]].  If one of the two computers has a gigabit ethernet card, a regular ethernet cable should work. Otherwise, use [[Wikipedia:Ethernet crossover cable|crossover cable]].</li>
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===Enable packet forwarding===
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Enter this command to temporaly enable packet forwarding:
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{{bc|<nowiki>sysctl net.ipv4.ip_forward=1</nowiki>}}
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Edit {{ic|/etc/sysctl.conf}} and add this line, which will make the previous change persistent after a reboot.
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{{bc|<nowiki>net.ipv4.ip_forward=1</nowiki>}}
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If you are using ipv6, use these lines:
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{{bc|<nowiki>
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net.ipv6.conf.default.forwarding=1
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net.ipv6.conf.all.forwarding=1
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</nowiki>}}
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===Enable NAT===
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[[pacman|Install]] the package {{Pkg|iptables}} from the [[Official Repositories|official repositories]].
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Use iptables to enable NAT:{{bc|<nowiki>
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# iptables -t nat -A POSTROUTING -o internet0 -j MASQUERADE
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# iptables-save > /etc/iptables/iptables.rules
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# systemctl start iptables
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</nowiki>}}{{Note| Of course, this also works with a mobile broadband connection (usually called ppp0 on PC1)}}
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You can set {{ic|iptables.service}} to [[Daemon|auto start at boot]].
  
<li>Let's assume that the first card (with the Internet) is called '''''internet0''''' and the other one (for the sharing) is called '''''local0'''''. (If those two keep switching at every boot read [[Udev#Setting static device names]]). The network interface of the client machine will be called '''''local1'''''.
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Read the [[iptables]] article for more information.
  
The interfaces '''''local0''''' and '''''local1''''' will have to be in the same network.</li>
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===Assigning ip addresses to the client pc(s)===
 
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If you are planning to regularly have several machines using the internet shared by this machine, then is a good idea to install a [[Wikipedia:dhcp|dhcp server]].
<li>Configure the second network card with:
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:'''IP:''' 192.168.0.1
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:'''Netmask:''' 255.255.255.0
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or enter in a console (as root)
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<pre>ifconfig local0 192.168.0.1 netmask 255.255.255.0
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ifconfig local0 up</pre></li>
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<li>To make this permanent, install [[netcfg]] if you don't have it and set up a network profile in '''/etc/network.d''', drawing on the examples in '''/etc/network.d/examples'''.  Or, put the above lines in '''/etc/rc.local'''.
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<li>Enable packet forwarding. To do so, write a "'''1'''" to '''/proc/sys/net/ipv4/ip_forward''' with:
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{{bc|1=sysctl net.ipv4.ip_forward=1}}
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<li>Edit '''/etc/sysctl.conf''' and add this line, which will make the previous change persistent after a reboot.
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<pre>net.ipv4.ip_forward=1</pre>
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If you are using ipv6, use these lines:
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<pre>net.ipv6.conf.default.forwarding=1
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net.ipv6.conf.all.forwarding=1</pre></li>
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<li>Install iptables, enable NAT (needed to share Internet), save and start it.
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You can read the [[dhcpd]] wiki article, to add a dhcp server. Then, install the [[dhcpcd]] client on every client pc.
<pre>pacman -S iptables
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iptables -t nat -A POSTROUTING -o internet0 -j MASQUERADE
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rc.d save iptables
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rc.d start iptables</pre></li>
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<li>Add iptables in your DAEMONS array in your /etc/rc.conf so that it is started each time.</li>
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If you are not planing to use this setup regularly, you can manually add an ip to each client instead.
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====Manually adding an ip====
  
<li>Go to the client PC and set:
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Instead of using dhcp, on each client pc, add an ip address and the default route:
:'''IP:''' 192.168.0.2
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{{bc|<nowiki>
:'''Netmask:''' 255.255.255.0
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ip addr add 139.96.30.120/24 dev eth0
:'''Gateway:''' 192.168.0.1
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ip link set up dev eth0
:'''DNS:''' The same DNS as the first PC
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ip route add default via 139.96.30.100 dev eth0
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</nowiki>}}
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Add a nameserver:
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{{bc|<nowiki>
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echo "nameserver <nameserver ip>" >> /etc/resolv.conf
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</nowiki>}}
  
<pre>ifconfig local1 192.168.0.2 netmask 255.255.255.0
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You can figure out the address of the nameserver by looking into the {{ic|/etc/resolv.conf}} of the server, if its Internet connection is already established.
ifconfig local1 up
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route add default gw 192.168.0.1 local1
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echo "nameserver <adr of nameserver>" >> /etc/resolv.conf
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</pre>
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You can figure out the address of the nameserver by looking into the /etc/resolv.conf of PC1, if its Internet connection is already established. If you don't have a nameserver, you can use [https://code.google.com/speed/public-dns/ Google Public DNS] which is relatively fast. Its addresses are '''8.8.8.8''' and '''8.8.4.4'''.</li></ol>
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If you don't have a nameserver, you can use any of the free public DNS servers, which are relatively fast:
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* [https://code.google.com/speed/public-dns/ Google Public DNS]
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** 8.8.8.8
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** 8.8.4.4
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** [2001:4860:4860::8888]
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** [2001:4860:4860::8844]
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* [https://opendns.com OpenDNS]:
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** 208.67.222.222
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** 208.67.220.220
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** [2620:0:ccc::2]
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** [2620:0:ccd::2]
  
{{Note| Of course, this also works with a mobile broadband connection (usually called ppp0 on PC1)}}
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Bracket notation must be used for IPv6 addresses in resolv.conf.
  
 
That's it. The client PC should now have Internet.
 
That's it. The client PC should now have Internet.

Revision as of 21:15, 12 July 2013

This article explains how to share the internet connection from one machine to other(s).

Requirements

  • The machine acting as server should have an additional network device
  • That network device should be connected to the machines that are going to receive internet access. They can be one or more machines. To be able to share internet to several machines a switch is required. If you are sharing to only one machine, a crossover cable is sufficient
Note: If one of the two computers has a gigabit ethernet card, a crossover cable is not necessary and a regular ethernet cable should be enough

Configuration

Using Udev#Setting static device names, name the network device connected to the other computer(s) as net0 and the network device connected to the internet as internet0.

Static IP address

Assign an static IPv4 address to the interface connected to the other machines. The first 3 bytes of this address cannot be exactly the same as those of another interface.

# ip link set up dev net0
# ip addr add 139.96.30.100/24 dev net0 # arbitrary address

To have your static ip assigned at boot, you can use netctl.

Enable packet forwarding

Enter this command to temporaly enable packet forwarding:

sysctl net.ipv4.ip_forward=1

Edit /etc/sysctl.conf and add this line, which will make the previous change persistent after a reboot.

net.ipv4.ip_forward=1

If you are using ipv6, use these lines:

net.ipv6.conf.default.forwarding=1
net.ipv6.conf.all.forwarding=1

Enable NAT

Install the package iptables from the official repositories.

Use iptables to enable NAT:
# iptables -t nat -A POSTROUTING -o internet0 -j MASQUERADE
# iptables-save > /etc/iptables/iptables.rules
# systemctl start iptables
Note: Of course, this also works with a mobile broadband connection (usually called ppp0 on PC1)

You can set iptables.service to auto start at boot.

Read the iptables article for more information.

Assigning ip addresses to the client pc(s)

If you are planning to regularly have several machines using the internet shared by this machine, then is a good idea to install a dhcp server.

You can read the dhcpd wiki article, to add a dhcp server. Then, install the dhcpcd client on every client pc.

If you are not planing to use this setup regularly, you can manually add an ip to each client instead.

Manually adding an ip

Instead of using dhcp, on each client pc, add an ip address and the default route:

ip addr add 139.96.30.120/24 dev eth0
ip link set up dev eth0
ip route add default via 139.96.30.100 dev eth0

Add a nameserver:

echo "nameserver <nameserver ip>" >> /etc/resolv.conf

You can figure out the address of the nameserver by looking into the /etc/resolv.conf of the server, if its Internet connection is already established.

If you don't have a nameserver, you can use any of the free public DNS servers, which are relatively fast:

  • Google Public DNS
    • 8.8.8.8
    • 8.8.4.4
    • [2001:4860:4860::8888]
    • [2001:4860:4860::8844]
  • OpenDNS:
    • 208.67.222.222
    • 208.67.220.220
    • [2620:0:ccc::2]
    • [2620:0:ccd::2]

Bracket notation must be used for IPv6 addresses in resolv.conf.

That's it. The client PC should now have Internet.

Troubleshooting

If you are able to connect the two PCs but cannot send data (for example, if the client PC makes a DHCP request to the server PC, the server PC receives the request and offers an IP to the client, but the client does not accept it, timing out instead), check that you don't have other Iptables rules interfering.

See also