Pour lever l'incertitude, il suffit de visualiser l'indicateur booléen “ip_forward”.

# nano /proc/sys/net/ipv4/ip_forward 1

• si ip_forward = 1, alors le routage IP est activé,
• si ip_forward = 0, alors le routage IP est inactivé.

# echo 1 > /proc/sys/net/ipv4/ip_forward
# nano  /proc/sys/net/ipv4/ip_forward

On peut aussi utiliser la commande sysctl :

# sysctl -w net.ipv4.ip_forward=1 net.ipv4.ip_forward = 1

# echo 0 > /proc/sys/net/ipv4/ip_forward

# nano  /proc/sys/net/ipv4/ip_forward

On peut aussi utiliser la commande sysctl :

# sysctl -w net.ipv4.ip_forward=0 net.ipv4.ip_forward = 0

Pour rendre le routage permanent, il faut ajouter (ou activer) cette ligne :

net.ipv4.ip_forward=1

dans le fichier /etc/sysctl.conf de configuration des variables système :

# cat /etc/sysctl.conf

# # /etc/sysctl.conf - Configuration file for setting system variables # See /etc/sysctl.d/ for additional system variables. # See sysctl.conf (5) for information. #

#kernel.domainname = example.com

# Uncomment the following to stop low-level messages on console #kernel.printk = 3 4 1 3

##############################################################3 # Functions previously found in netbase #

# Uncomment the next two lines to enable Spoof protection (reverse-path filter) # Turn on Source Address Verification in all interfaces to # prevent some spoofing attacks #net.ipv4.conf.default.rp_filter=1 #net.ipv4.conf.all.rp_filter=1

# Uncomment the next line to enable TCP/IP SYN cookies # See http://lwn.net/Articles/277146/ # Note: This may impact IPv6 TCP sessions too #net.ipv4.tcp_syncookies=1

# Uncomment the next line to enable packet forwarding for IPv4 #net.ipv4.ip_forward=1

# Uncomment the next line to enable packet forwarding for IPv6 # Enabling this option disables Stateless Address Autoconfiguration # based on Router Advertisements for this host #net.ipv6.conf.all.forwarding=1

Pour que le fichier de configuration soit relu, il faut, par exemple, entrer la commande :

# sysctl -p /etc/sysctl.conf