Lab ZFW

R1+++++++++++++++++++++++++++++++++++++++++++++++++++++

interface Serial1/2
 ip address 12.1.1.1 255.255.255.0
 serial restart-delay 0
!
!
ip route 23.1.1.0 255.255.255.0 12.1.1.2

R2++++++++++++++++++++++++++++++++++++++++++++++++++++++
class-map type inspect match-any CLASS
 match protocol tcp
 match protocol icmp
 match protocol udp
!
!
policy-map type inspect POLICY
 class type inspect CLASS
  inspect
 class class-default
!
zone security private
zone security public
zone-pair security PAIR source private destination public
 service-policy type inspect POLICY

interface Serial1/2
 ip address 12.1.1.2 255.255.255.0
 zone-member security private
 serial restart-delay 0
!
interface Serial1/3
 ip address 23.1.1.2 255.255.255.0
 zone-member security public
 serial restart-delay 0

R3++++++++++++++++++++++++++++++++++++++++++++++++++

interface Serial1/3
 ip address 23.1.1.3 255.255.255.0
 serial restart-delay 0
!
ip route 12.1.1.0 255.255.255.0 23.1.1.2

+++++++++++++++++++++++++++++++++++++++++++++

Test
R3:
R3#ping 12.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

R1:
R1#ping 23.1.1.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 23.1.1.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/60/100 ms