I have configured a mikrotik RB450 OS v4.11 as a gateway router.My ISP has given me two public IP series one for the WAN with /30 netmask and another series with /28 netmask for the LAN of the router.On the LAN side of the router I have installed authentication and management server. on the WAN of the server I have assigned one public IP with /28 netmask which is on the same subnet with the router LAN.everythings working fine,but I have problems doing remote administration of server as I cannot do remote login.I'am able to ping and winbox WAN of the router, but unable to ping LAN of the router on public IP and WAN of the management server or log into it.pls help.

The /30 IP address should be on the WAN interface, with a default route out via the ISP router on that network. An IP address on the /28 should be on the LAN interface (not the WAN interface), then the server gets an IP on the same network and a default gateway equal to the router address on the /28. Also ensure you're not blocking traffic in the IP firewall filters.

If you need more specific help post the output of "/ip address print detail", "/ip route print detail", "/interface print", "/ip firewall export", and an accurate network diagram.

seems like a have the same problem

I'am attaching screen shot details of IP address,IP route,IP firewall and interface config on the router.

internet (isp)
|
122.181.13.72/30 (router WAN)
|
122.181.171.192/28 (router LAN)
|
122.181.171.194/28 (management server WAN)

You don't need any dst-nat rule in there.

Again: /30 address on WAN, /28 on your LAN side.
Any address on the LAN side should be on teh /28 subnet.