Ip_forwarding and NAT on GL-MT300N-V2 / Mango

Technical Support for Routers
1

I’m trying to use my router as an internet edge gateway for my ZeroTier network. For this, I need to enable ip_forwarding and NAT. On a CentOS, I would do the following:

sysctl net.ipv4.ip_forward=1

def=$(ip route | grep ^default | awk '{ print $5 }')

for iface in $(ls /sys/class/net | grep $def) ; do 
    iptables -t nat -A POSTROUTING -o "${iface}" -j MASQUERADE ;
    ip6tables -t nat -A POSTROUTING -o "${iface}" -j MASQUERADE ;
done

I tried the same on my OpenWRT device and nothing seems to happen, not even an error. Can someone help me here?

2

what firmware version are you using?

3

I am the OEM firmware. I got this to work by adding firewall rules. IP forwarding was enabled by default.

4

In my modem, the forwarding is enabled by default. You can verify it by invoking:

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

You do not need to duplicate the postrouting rules; they are already there. You just need to enable them correctly from the Firewall in Luci. You can verify you existing rules:

# iptables -t nat -L | awk 'BEGIN{IGNORECASE = 1}/POSTROUTING/,/^$/'
Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
postrouting_rule  all  --  anywhere             anywhere             /* !fw3: Custom postrouting rule chain */
zone_lan_postrouting  all  --  anywhere             anywhere             /* !fw3 */
zone_wan_postrouting  all  --  anywhere             anywhere             /* !fw3 */

Chain postrouting_lan_rule (1 references)
target     prot opt source               destination         

Chain postrouting_rule (1 references)
target     prot opt source               destination         

Chain postrouting_wan_rule (1 references)
target     prot opt source               destination         

Chain zone_lan_postrouting (1 references)
target     prot opt source               destination         
postrouting_lan_rule  all  --  anywhere             anywhere             /* !fw3: Custom lan postrouting rule chain */

Chain zone_wan_postrouting (1 references)
target     prot opt source               destination         
postrouting_wan_rule  all  --  anywhere             anywhere             /* !fw3: Custom wan postrouting rule chain */
MASQUERADE  all  --  anywhere             anywhere             /* !fw3 */