I have one Mikrotik RouterBoard RB450G.
My requirement is configuring one port for WAN and other ports for LAN.
I configure the second port for LAN with IP: 192.168.168.1/24.
When I start using it, I can not connect to the third port to get IP: 192.168.168.0/24 the same as the second port.

I mean I want to configure one port for WAN and other 4 ports for LAN look like other Wireles Routers with one built-in port as WAN and others for LAN.

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Tepsayut
Network Technician

If you mean you cannot connect to ips on a different interface, then the most common problem is the nat. If the srcnat/masquerade does not have an out-interface set, then you should add one.
/ip firewall nat
set X out-interface=ether1
If ether1 is not the wan interface, change to the appropriate interface.

Have you bridged ports 2-5?

If not, do that and assign the lan ip 192.168.168.1/24 to the bridge, not port 2.

All 4 ports are now bridged and the router has 192.168.168.1/24.
192.168.168.0/24 is now reachable on all 4 ports, assuming firewall settings are correct.

You can restrict bridge traffic using the firewall if you have firewall enabled on the bridge.

Set masquerade as SurferTim notes to access anything that is not local to the router, out the wan port.

If you need wire speed on the lan side, look into using the switch chip - way cool.