Enabling remote SSH access in OpenWRT is a two-step process. SSH access must be enabled on the WAN, and the SSH port must be opened in the firewall.
1. Enable ssh access on the WAN Go to System->Administration. Under SSH Access, make sure "unspecified" is selected for Interface. This allows SSH access on both the LAN and WAN interfaces.
2. Now, open the appropriate port in your firewall. There are two ways to accomplish this. You can either add changes to /etc/firewall.user or /etc/config/firewall.

A. To use the first method, add the following lines to /etc/firewall.user. Note the example below specifies port 22 as the SSH port.
iptables -t nat -A prerouting_wan -p tcp --dport 22 -j ACCEPT iptables -A input_wan -p tcp --dport 22 -j ACCEPT

B. To use the second method, add the following to /etc/config/firewall. Note the example below specifies port 22 as the SSH port.

config rule
    option name 'WAN-MGMT-22'
    option src wan
    option dest_port 22
    option target ACCEPT
    option proto tcp
 
config rule
    option name 'WAN-MGMT-80'
    option src 'wan'
    option dest_port '80'
    option target 'ACCEPT'
    option proto tcp