i'm not sure if I understan you well.
on console (local) use:
links 127.0.0.1/server-manager
than look into remote access on left side panel.
pls also check if the external network and internal aren't the same. there is no chance to route from one network to the same one on second interface with NAT.
ex. bad situation
PC ------------------ eth0-----SME-----eth1 -------MODEM
IP 10.0.0.123 IP 10.0.0.1 IP 10.0.0.25 IP 10.0.0.24
M 255.255.255.0 M 255.255.255.0 M 255.255.255.0 M 255.255.255.0
G 10.0.01 G 10.0.0.24 G 88.99.111.222 (some public IP - i know that the gateway on picture should be from the same network (ex 10.0.0.255) by public ip i mean Internet or any public network. )
good situation
PC ------------------ eth0-----SME-----eth1 -------MODEM
IP 172.16.13.123 IP 172.16.13.1 IP 10.0.0.25 IP 10.0.0.24
M 255.255.255.0 M 255.255.255.0 M 255.255.255.0 M 255.255.255.0
G 172.16.13.1 G 10.0.0.24 G 88.99.111.222 (some public IP)
what you have written is not very precise
the server ip is 10.xx.xx.100
the router ip is 10.xx.xxx.1
gateway is 10.xx.xx.100
range for dchp is 10.xx.xx.2 - 10.xx.xx.99
why there are two x or three x.
write exacly ip addresses you may change your public ip if you are affraid.
lets use public ip 88.99.111.222 (or full network)