You needn't have to do any configuration on the router if its in bridged mode. Are you sure that its working in the bridged mode and the public IP ( 59.83.xxx.xxx ) is getting assigned to your ethernet interface? ( ethX ) ? Check it out first.
Yes ,the router is configured in Bridge mode and the public IP is assigned to the ethernet interface. (eth1)
Next, you need to check out if ssh is listening on your ethernet
interface or not. For that you'll need to check out sshd's config file. Sometimes with multiple interfaces, sshd listens only on a particular interface and thats where the problem begins.
From the local LAN I am able to SSH to this gateway.
Does it imply that sshd is listening to only the local eth0 interface ?
Also, you needn't use the bridged mode for opening up ssh service to the
outside world. You could use portforwarding ( or in some cases "virtual server" ) to make the sshd available over the internet..
BTW which distro are you using?
I am using RH 7.3.
Hozefa