Yes, you probably need to adjust your firewall rules. To see your current rules:
If you see a bunch of ACCEPT rules and a REJECT rule at the end, that means your host is blocking all incoming connections except the specified ones.
I think you can use the
system-config-securitylevel menu-based tool to open custom ports. Run that program in a terminal and choose the 'customize' button. Add
3899:tcp to the other ports list and save your changes. I'm not sure if system-config-securitylevel takes port numbers instead of service names. If specifying the port number in that tool doesn't work, you can try adding your custom 'myssh' service name to
/etc/services and then using that name in system-config-securitylevel.
You can run
nmap -sS -v server.example.com
from an outside machine to scan your system to determine which ports are open.
Another way to make this change is to hand edit
/etc/sysconfig/iptables, and copy the existing ssh entry to another entry right below it, but change the port from ssh to 3899. Note that it's easy to screw up your firewall config by hand-editing the iptables file, so be very cautious if you go this route. After you make changes, reboot the machine, or run
/etc/init.d/iptables restart to load your changes.