Category: Networking

Before I begin, uPnP does have some security implications. Users that can send uPnP requests can open any port to any other computer. Please read the comments below for more details.

If you are currently using a Linux router on a home network, you should consider uPnP. uPnP allows computers to request ports be opened for them, so applications that require open ports can work without work of the owner of the Linux router.

apt-get install libupnp0 linux-igd

Edit /etc/default/upnpd and specify your external and internal interfacecs; upnp does not support multiple interfaces but I suspect multiple instances of this program could accomplish this; just replace the /etc/init.d/upnpd file with a custom one like this

#!/bin/bash

case $1 in

start)

upnpd eth0 eth1

upnpd eth0 eth2

;;

stop)

killall upnpd

;;

esac

Restart the daemon, and you should see clients requesting ports in /var/log/syslog (grep for upnp).

If you do not, make sure that you see the following line in “route”

239.0.0.0       *               255.0.0.0       U     0      0        0 eth3

Where eth3 is your internal interface. If not, add it with

route add -net 239.0.0.0 netmask 255.0.0.0 eth3

Also, if you are blocking any ports with your firewall configuration, you may have to do the following to allow your clients request to reach the server.

iptables -A INPUT -s 192.168.1.0/24 -p tcp --dport 2869 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -p udp --dport 1900 -j ACCEPT


Where 192.168.1.0/24 is your internal network.

A good way to test to make sure this is working is using the Azureus bittorrent client’s NAT checking tool.

Below is a two network firewall script that I am currently using with uPnP; I can’t make any guarantees to how secure it is but it works quite well.


IP2="76.249.179.145"
IP3="76.249.179.147"
/sbin/ip addr add dev eth0 $IP2
/sbin/ip addr add dev eth0 $IP3
/sbin/depmod -a
/sbin/modprobe ip_tables
/sbin/modprobe ip_conntrack
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe ip_conntrack_irc
/sbin/modprobe iptable_nat
/sbin/modprobe ip_nat_ftp
/sbin/modprobe ip_nat_irc
IPT="/sbin/iptables"
INT0="eth0"
INT2="eth2"
INT3="eth3"
echo "1" > /proc/sys/net/ipv4/ip_forward
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
echo "65535" > /proc/sys/net/ipv4/ip_conntrack_max
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
echo "1" > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
echo "1" > /proc/sys/net/ipv4/conf/all/accept_redirects
echo "0" > /proc/sys/net/ipv4/conf/all/log_martians
echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
echo 9000 > /proc/sys/net/ipv4/tcp_keepalive_time
echo 1 > /proc/sys/net/ipv4/tcp_window_scaling
echo 0 > /proc/sys/net/ipv4/tcp_sack
echo 3000 > /proc/sys/net/ipv4/tcp_max_syn_backlog
$IPT -F
$IPT -X
$IPT -Z
$IPT -P INPUT DROP
$IPT -P FORWARD ACCEPT
$IPT -P OUTPUT ACCEPT
$IPT -N DROPLOG
$IPT -A DROPLOG -j ULOG -m limit --limit 2/hour --ulog-nlgroup 1 --ulog-qthreshold 20
$IPT -A DROPLOG -j REJECT
$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A INPUT -i lo -j ACCEPT
$IPT -A INPUT -i $INT2 -j ACCEPT
$IPT -A INPUT -i $INT3 -j ACCEPT
$IPT -A FORWARD -i $INT3 -o $INT0 -j ACCEPT
$IPT -A FORWARD -i $INT0 -o $INT3 -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A FORWARD -i $INT2 -o $INT0 -j ACCEPT
$IPT -A FORWARD -i $INT0 -o $INT2 -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -t nat -A POSTROUTING -s 192.168.1.0/24 -o eth0 -j SNAT --to-source $IP2
$IPT -t nat -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j SNAT --to-source $IP3
$IPT -t nat -A POSTROUTING -s 192.168.1.0/24 -o eth0 -j MASQUERADE
$IPT -t nat -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j MASQUERADE
$IPT -t nat -A POSTROUTING -s 192.168.2.48 -d 192.168.0.0/16 -j ACCEPT
$IPT -t nat -A POSTROUTING -s 192.168.0.0/16 -d 192.168.2.48 -j ACCEPT
$IPT -t nat -A POSTROUTING -s 192.168.1.1 -d 192.168.1.240 -j ACCEPT
$IPT -t nat -A POSTROUTING -s 192.168.1.240 -d 192.168.1.1 -j ACCEPT
$IPT -t nat -A POSTROUTING -s 192.168.2.48 -d 192.168.1.0/16 -j ACCEPT
$IPT -A INPUT -p tcp --dport 22 -j ACCEPT
$IPT -A INPUT -p tcp --dport 80 -j ACCEPT
#Allow uPnP from internal clients
$IPT -A INPUT -s 192.168.1.0/24 -p tcp --dport 2869 -j ACCEPT
$IPT -A INPUT -s 192.168.1.0/24 -p udp --dport 1900 -j ACCEPT
$IPT -A INPUT -s 192.168.2.0/24 -p tcp --dport 2869 -j ACCEPT
$IPT -A INPUT -s 192.168.2.0/24 -p udp --dport 1900 -j ACCEPT
$IPT -A INPUT -i eth2 -j ACCEPT
$IPT -A INPUT -i eth3 -j ACCEPT
$IPT -A INPUT -s 192.168.20.0/24 -j ACCEPT
$IPT -A INPUT -p tcp -s 192.168.1.0/24 --dport 3128 -j ACCEPT
$IPT -A INPUT -p tcp -s 192.168.2.0/24 --dport 3128 -j ACCEPT
$IPT -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 192.168.1.1:3128
$IPT -t nat -A PREROUTING -i eth2 -p tcp --dport 80 -j DNAT --to 192.168.1.1:3128
$IPT -t nat -A PREROUTING -i eth3 -p tcp --dport 80 -j DNAT --to 192.168.1.1:3128
$IPT -t nat -A PREROUTING -i eth4 -p tcp --dport 80 -j DNAT --to 192.168.1.1:3128
$IPT -t nat -A PREROUTING -i eth5 -p tcp --dport 80 -j DNAT --to 192.168.1.1:3128
$IPT -A INPUT -i eth0 -p tcp --syn --destination-port 3128 -j DROPLOG
$IPT -A INPUT -j DROPLOG


When you use sftp/scp to transfer directories, you notice it ends up taking a long time. It works on files one at a time and they can often take a small amount of time to start and finish. A solution is to use tar to stream the file over ssh (so you have one continuious stream, without starting/stopping a lot).

ssh [email protected] “tar cf – big_dir/” | tar xf –

I timed transferring a 330MB directory with more than 3600 files in it.

Transferring over 10/100 Ethernet over SMBFS with ‘cp -r’

real    2m45.495s
user    0m0.100s
sys     0m4.424s

Transferring over 54mb WiFi (at 70% signal strength) using ssh/tar

real    2m8.800s
user    0m12.377s
sys     0m10.501s

Transfering over 10/100 Ethernet using ssh/tar

real    0m37.929s
user    0m5.628s
sys     0m4.068s

It took 37 less seconds over wireless (pretty impressive, especially when dealing with only 330MB). It was a full 2 MINUTES (and 8 seconds) faster over the same kind of connection.

This is useful both in a LAN enviornment and over the internet.