connect internal lans, one-way

[Richard Langly]

How do I allow for GigabitEthernet1/2 to talk to GigabitEthernet1/5 but not allow 5 to talk to 2? Each one of them successfully talks to outside.

interface GigabitEthernet1/1
 nameif outside
 security-level 0
 ip address dhcp setroute
!
interface GigabitEthernet1/2
 nameif inside
 security-level 100
 ip address 192.168.1.1 255.255.255.0
!
interface GigabitEthernet1/3
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet1/4
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet1/5
 nameif wlan
 security-level 60
 ip address 192.168.3.1 255.255.255.0
!

[Deepak Kumar]

Its a directly connected interface to the router, it will always be reachable together from Router, 

But we can stop services by applying access list to the interface.

Example : PING, Echo, Echo-reply, telnet. etc.

[Henrik Grankvist]

If you leave it as you have it right now, without any access lists, it will fulfil your requirements.

Gi1/2 has higher security-level than Gi1/5, so Gi1/2 will be able to initiate traffic to Gi1/5, but not the other way around.