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1. Configurare un router su Ubuntu

1.1. Intriduzione

Questo articolo esiste a causa della mancanza di informazioni concise e sono facilmente seguibili le istruzioni sull'argomento delle configurazioni di un router per la navigazione via cavo o wireless su Ubuntu. Questo è destinato per gli utenti intermedi e avanzati che devono o a cui piacerebbe configurare un'installazione apposita per Ubuntu del router di casa o nel loro ufficio. Il risultato è un potente router che può fornire funzionalità simili a prodotti popolari (per esempio, il Linksys WRT54G).

1.2. Descrizione tecnica

The router that will be created is an Internet gateway for wired and/or wireless clients to share one broadband connection with one IP address.

The basics this router will provide are:

• A firewall

  • IP_masquerading

  • port forwarding (optional)
• DHCP server
• DNS caching server

2. Prerequisites

2.1. Broadband Connection

A broadband connection like a cable or DSL modem is required. Your broadband service provider must either provide the necessary information to configure your IP address statically or provide a dynamically assigned address via DHCP.

2.2. Router Hardware

You'll need a dedicated computer to act as the router. The computer can use old hardware and having the minimum requirements to install Ubuntu should suffice. The author of this article runs his router on a P3 600mhz processor with 256MB of RAM. You are encouraged use this as a server for other applications perhaps by installing postfix, apache, mysql, and/or samba. This guide recommends a server installation of Ubuntu, but there's no reason why a desktop installation wouldn't work. If you plan to be able to access the router remotely, install ssh before proceeding.

The following needs to be physically installed and recognized by the kernel on your router:

• A network adapter connected to the broadband cable or DSL modem

• For a wired network,

  • Another network adapter connected to a hub or switch

• For a wireless network,

  • A wireless network adapter (which must be able to be set in "master" mode)

    • sudo iwconfig <device name> mode master should not return an error

    • If your wireless network adapter is not recognized by your server installation of Ubuntu, it may use the madwifi chipset (like the D-Link DWL-G520). Please visit ["Router/Madwifi"] for more information.

• For both a wired and wireless network,

  • All of the above

Running ifconfig -a will show you what network interfaces are available.

3. Internal Network Information

Here are the values we'll use to set up your internal network. Advanced users use caution when changing them as the changes will need to be reflected in all further router configuration.

4. Setting Up Your Network Interfaces

4.1. Device Naming Overview

It is important to note that the names of the network devices above (eth0, eth1, and wlan0) are used as convention. It is very likely that your router will recognize its devices under different names (for example, madwifi calls its wireless device ath0). Please substitute the names of your device accordingly. For information about how to change the names of your network devices, try man iftab.

4.2. Taking a Backup

Issue the following command to take a backup of your current network configuration:

• {{{sudo cp /etc/network/interfaces /etc/network/interfaces.bak

}}}

4.3. Configuring the External Network Interface

4.3.1. Setting up External Network Interface

Here, we configure the Ubuntu networking system to bring the the local loopback and external network interfaces up by editing /etc/networking/interfaces. The primary goal here is to set up your external network interface (eth0, or whatever you're using in place of it) to be brought up by the networking subsystem. The examples below are only for the most basic setups. If your setup requires additional configuration, for example you need to setup [:ADSLPPPoE:ADSL with PPPoE], adapt the following examples so that the end result is your external network interface connected to the Internet.

4.3.1.1. For Dynamic IP Addresses (DHCP) Only

Open /etc/network/interfaces with your favourite editor. Delete everything and paste in what is below. Follow the commented out instructions carefully.

• {{{# Set up the local loopback interface

auto lo iface lo inet loopback

# Set up the external interface # # Don't forget to change eth0 to the proper name of the external # interface if applicable. # auto eth0 iface eth0 inet dhcp}}}

4.3.1.2. For Static IP Address Only

Open /etc/network/interfaces with your favourite editor. Delete everything and paste in what is below. Follow the commented out instructions carefully.

• {{{# Set up the local loopback interface

auto lo iface lo inet loopback

# Set up the External interface # # For every xxx.xxx.xxx.xxx, enter the numeric address given to you # by your Internet provider. Don't forget to change eth0 to the proper # name of the external interface if applicable. # auto eth0 iface eth0 inet static

• address xxx.xxx.xxx.xxx netmask xxx.xxx.xxx.xxx gateway xxx.xxx.xxx.xxx}}}

Now, set up your DNS servers as given to you by your service provider in /etc/resolv.conf, which should look something like this

• {{{nameserver xxx.xxx.xxx.xxx

nameserver xxx.xxx.xxx.xxx}}}

You can visit the [https://help.ubuntu.com/6.06/ubuntu/serverguide/C/network-configuration.html Ubuntu Server Guide - Network Configuration] documentation for more information

4.3.2. Testing Connectivity

Reload the network configuration and test for connectivity,

• {{{sudo /etc/init.d/networking restart

ping -c 3 -W 10 ubuntu.com}}} And if all goes well something similar should return:

• {{{PING ubuntu.com (82.211.81.166) 56(84) bytes of data.

64 bytes from signey.ubuntu.com (82.211.81.166): icmp_seq=1 ttl=43 time=99.9 ms 64 bytes from signey.ubuntu.com (82.211.81.166): icmp_seq=2 ttl=43 time=109 ms 64 bytes from signey.ubuntu.com (82.211.81.166): icmp_seq=3 ttl=43 time=100 ms

--- ubuntu.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2001ms rtt min/avg/max/mdev = 99.982/103.450/109.419/4.254 ms}}}

4.4. Configuring the Internal Network Interfaces

4.4.1. Wired Only

Append the following to /etc/network/interfaces and follow the commented out instructions carefully.

• {{{# Set up the internal wired network

# # Don't forget to change eth1 to the proper name of the internal # wired network interface if applicable. # auto eth1 iface eth1 inet static

• address 192.168.0.1 network 192.168.0.0 netmask 255.255.255.0 broadcast 192.168.0.255}}}

Your internal network interface is: eth1 (or whatever you're using in place of it)

4.4.2. Wireless Only

If you plan on using WEP, generate a network key,

• {{{dd if=/dev/random bs=1 count=13 2>/dev/null | xxd -p

}}}

Append the following to /etc/network/interfaces and follow the commented out instructions carefully.

• {{{# Set up the internal wireless network

# # Don't forget to change wlan0 to the proper name of the internal # wireless network interface if applicable. # # If you would like to use WEP, uncomment the line 'wireless-key' # and replace '<key goes here>' with a WEP key. # # You may also change the network essid and channel. # auto wlan0 iface wlan0 inet static

• wireless-mode master

  wireless-essid "UbuntuWireless" wireless-channel 1 #wireless-key <key goes here> address 192.168.0.1 network 192.168.0.0 netmask 255.255.255.0 broadcast 192.168.0.255}}}

Your internal network interface is: wlan0 (or whatever you're using in place of it)

4.4.3. Both Wired and Wireless

First install the necessary tools to create a network bridge,

• {{{sudo apt-get install bridge-utils

}}}

If you plan on using WEP, generate a network key,

• {{{dd if=/dev/random bs=1 count=13 2>/dev/null | xxd -p

}}}

Append the following to /etc/network/interfaces and follow the commented out instructions carefully.

• {{{# Set up the internal wireless network

# # Don't forget to change wlan0 to the proper name of the internal # wireless network interface if applicable. # # If you would like to use WEP, uncomment the line 'wireless-key' # and replace '<key goes here>' with a WEP key. # # You may also change the network essid and channel. # auto wlan0 iface wlan0 inet manual

• wireless-mode master

  wireless-essid "UbuntuWireless" wireless-channel 1 #wireless-key <key goes here>

# Set up the internal wired network # # It's not necessary to bring this interface up as the bridge # we are about to create does this. Leave these lines commented. # #auto eth1 #iface eth1 inet manual

# Set up the internal wired/wireless network bridge # # Don't forget to change wlan0 and eth1 to the proper name of # the internal wired and wireless interfaces if applicable. # auto br0 iface br0 inet static

• address 192.168.0.1 network 192.168.0.0 netmask 255.255.255.0 broadcast 192.168.0.255 bridge-ports eth1 wlan0}}}

Your internal network interface is: br0

4.5. Restart Networking

Now, if the following command is executes successfully, your networking devices have been properly configured.

• {{{sudo /etc/init.d/networking restart

}}}

5. Configuring the Firewall

5.1. Background

5.2. The Firewall Script

This is a just a rough draft!

IPTABLES=/sbin/iptables
AWK=/usr/bin/awk
IFCONFIG=/sbin/ifconfig


# External (Internet-facing) interface
EXTIF="eth0"

# External IP address (automatically detected)
EXTIP="`$IFCONFIG $EXTIF | $AWK /$EXTIF/'{next}//{split($0,a,":");split(a[2],a," ");print a[1];exit}'`"
 
# Internal interface
INTIF="br0"

# Internal IP address (in CIDR notation)
INTIP="192.168.0.1/32"

# Internal network address (in CIDR notation)
INTNET="192.168.0.0/24"

# The address of anything/everything (in CIDR notation)
UNIVERSE="0.0.0.0/0"


echo "External: [Interface=$EXTIF] [IP=$EXTIP]"
echo "Internal: [Interface=$INTIF] [IP=$INTIP] [Network:$INTNET]"

echo
echo -n "Loading rules..."

# Enabling IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward


# Clear any existing rules and set the default policy to DROP
$IPTABLES -P INPUT DROP
$IPTABLES -F INPUT 
$IPTABLES -P OUTPUT DROP
$IPTABLES -F OUTPUT 
$IPTABLES -P FORWARD DROP
$IPTABLES -F FORWARD 
$IPTABLES -F -t nat

# Delete all User-specified chains
$IPTABLES -X

# Reset all IPTABLES counters
$IPTABLES -Z

###################################################
# INPUT: Incoming traffic from various interfaces #
###################################################

# Loopback interface is valid
$IPTABLES -A INPUT -i lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT


# Local interface, local machines, going anywhere is valid
$IPTABLES -A INPUT -i $INTIF -s $INTNET -d $UNIVERSE -j ACCEPT


# Remote interface, claiming to be local machines, IP spoofing, get lost
$IPTABLES -A INPUT -i $EXTIF -s $INTNET -d $UNIVERSE -j REJECT


# External interface, from any source, for ICMP traffic is valid
$IPTABLES -A INPUT -i $EXTIF -p ICMP -s $UNIVERSE -d $EXTIP -j ACCEPT


# Allow any related traffic coming back to the MASQ server in.
$IPTABLES -A INPUT -i $EXTIF -s $UNIVERSE -d $EXTIP -m state --state ESTABLISHED,RELATED -j ACCEPT


# Internal interface, DHCP traffic accepted
$IPTABLES -A INPUT -i $INTIF -p tcp --sport 68 --dport 67 -j ACCEPT
$IPTABLES -A INPUT -i $INTIF -p udp --sport 68 --dport 67 -j ACCEPT


# External interface, HTTP/HTTPS traffic allowed
$IPTABLES -A INPUT -i $EXTIF -m state --state NEW,ESTABLISHED,RELATED -p tcp -s $UNIVERSE -d $EXTIP --dport 80 -j ACCEPT
$IPTABLES -A INPUT -i $EXTIF -m state --state NEW,ESTABLISHED,RELATED -p tcp -s $UNIVERSE -d $EXTIP --dport 443 -j ACCEPT

# External interface, SSH traffic allowed
$IPTABLES -A INPUT -i $EXTIF -m state --state NEW,ESTABLISHED,RELATED -p tcp -s $UNIVERSE -d $EXTIP --dport 22 -j ACCEPT


# Catch-all rule, reject anything else
$IPTABLES -A INPUT -s $UNIVERSE -d $UNIVERSE -j REJECT


####################################################
# OUTPUT: Outgoing traffic from various interfaces #
####################################################

# Workaround bug in netfilter
$IPTABLES -A OUTPUT -m state -p icmp --state INVALID -j DROP

# Loopback interface is valid.
$IPTABLES -A OUTPUT -o lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT


# Local interfaces, any source going to local net is valid
$IPTABLES -A OUTPUT -o $INTIF -s $EXTIP -d $INTNET -j ACCEPT


# local interface, MASQ server source going to the local net is valid
$IPTABLES -A OUTPUT -o $INTIF -s $INTIP -d $INTNET -j ACCEPT


# outgoing to local net on remote interface, stuffed routing, deny
$IPTABLES -A OUTPUT -o $EXTIF -s $UNIVERSE -d $INTNET -j REJECT


# anything else outgoing on remote interface is valid
$IPTABLES -A OUTPUT -o $EXTIF -s $EXTIP -d $UNIVERSE -j ACCEPT


# Internal interface, DHCP traffic accepted
$IPTABLES -A OUTPUT -o $INTIF -p tcp -s $INTIP --sport 67 -d 255.255.255.255 --dport 68 -j ACCEPT
$IPTABLES -A OUTPUT -o $INTIF -p udp -s $INTIP --sport 67 -d 255.255.255.255 --dport 68 -j ACCEPT


# Catch all rule, all other outgoing is denied and logged. 
$IPTABLES -A OUTPUT -s $UNIVERSE -d $UNIVERSE -j REJECT


###########################
# Packet Forwarding / NAT #
###########################

# ----- Begin OPTIONAL FORWARD Section -----

#Optionally forward incoming tcp connections on port 1234 to 192.168.0.100
#$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -p tcp --dport 1234 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
#$IPTABLES -A PREROUTING -t nat -p tcp -d $EXTIP --dport 1234 -m state --state NEW,ESTABLISHED,RELATED -j DNAT --to 192.168.0.100:1234

# ----- End OPTIONAL FORWARD Section -----


# Accept solicited tcp packets
$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED  -j ACCEPT

# Allow packets across the internal interface
$IPTABLES -A FORWARD -i $INTIF -o $INTIF -j ACCEPT

# Forward packets from the internal network to the Internet
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT

# Catch-all REJECT rule
$IPTABLES -A FORWARD -j REJECT

# IP-Masquerade
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j SNAT --to $EXTIP


echo " done."

6. DHCP and DNS

7. Ulteriori risorse

• [https://help.ubuntu.com/community/Router Documento originale]

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