NAT Static

I wont talk about what NATing does in this article. However, I will show you some basic configuration of NAT to clarify everyone understanding.


Configuration example

Configuration

R2

interface FastEthernet0/0

 ip address 192.168.1.2 255.255.255.0

 ip nat inside

 ip virtual-reassembly

 duplex auto

 speed auto

!

interface FastEthernet0/1

 ip address 192.168.2.1 255.255.255.0

 ip nat outside

 ip virtual-reassembly

 duplex auto

 speed auto

!

router ospf 1

 log-adjacency-changes

 network 192.168.1.2 0.0.0.0 area 0

 network 192.168.2.1 0.0.0.0 area 0

!

ip http server

no ip http secure-server

!

ip route 2.2.2.0 255.255.255.0 192.168.2.2

// from inside to outside : route before translate

!

ip nat inside source static 1.1.1.1 172.16.1.1

ip nat outside source static 3.3.3.3 2.2.2.2

!

Providing route for R1 and R3 to pass the traffic through R2 to translate

R1

ip route 2.2.2.2 255.255.255.255 192.168.1.2

R2

ip route 172.16.1.0 255.255.255.0 192.168.2.1

Verify Configuration

R1#ping 2.2.2.2 source 1.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:

Packet sent with a source address of 1.1.1.1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 12/66/176 ms

R1#

R3#ping 172.16.1.1 source 3.3.3.3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:

Packet sent with a source address of 3.3.3.3

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 24/71/144 ms

R3#

R2#show ip nat translations

Pro Inside global      Inside local       Outside local      Outside global

--- ---                ---                2.2.2.2            3.3.3.3

icmp 172.16.1.1:2      1.1.1.1:2          2.2.2.2:2          3.3.3.3:2

icmp 172.16.1.1:8      1.1.1.1:8          2.2.2.2:8          3.3.3.3:8

--- 172.16.1.1         1.1.1.1            ---                ---

R2#

R2 debug ip nat

Mar  1 00:32:18.007: NAT*: s=3.3.3.3->2.2.2.2, d=172.16.1.1 [41]

*Mar  1 00:32:18.007: NAT*: s=2.2.2.2, d=172.16.1.1->1.1.1.1 [41]

*Mar  1 00:32:18.035: NAT*: s=1.1.1.1->172.16.1.1, d=2.2.2.2 [42]

*Mar  1 00:32:18.035: NAT*: s=172.16.1.1, d=2.2.2.2->3.3.3.3 [42]

*Mar  1 00:32:18.051: NAT*: s=3.3.3.3->2.2.2.2, d=172.16.1.1 [42]

*Mar  1 00:32:18.051: NAT*: s=2.2.2.2, d=172.16.1.1->1.1.1.1 [42]

*Mar  1 00:32:18.063: NAT*: s=1.1.1.1->172.16.1.1, d=2.2.2.2 [43]

*Mar  1 00:32:18.063: NAT*: s=172.16.1.1, d=2.2.2.2->3.3.3.3 [43]