Um IP forwarding zu aktivieren öffne bitte die Datei /etc/sysctl.conf mit einem Editor deiner Wahl:

# Kernel sysctl configuration file for Red Hat Linux
#
# For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and
# sysctl.conf(5) for more details.

# Controls IP packet forwarding
net.ipv4.ip_forward = 1

# Controls source route verification
net.ipv4.conf.default.rp_filter = 1

# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0

# Controls the System Request debugging functionality of the kernel
kernel.sysrq = 0

# Controls whether core dumps will append the PID to the core filename.
# Useful for debugging multi-threaded applications.
kernel.core_uses_pid = 1

und setze dort die Variable net.ipv4.ip_forward = 1

Die Änderungen kannst du daraufhin durch Eingabe von:

sysctl -p

überprüfen.