NAT configuration with GNS3. How I can test config?

Unanswered Question
Aug 15th, 2009

I have configured this test config for learning NAT:

on router. How I can test and understood work of it?

Thank you!

access-list 1 remark ACL Category=2

access-list 1 permit

interface FastEthernet0/1

ip nat outside


interface FastEthernet0/0

ip nat inside


ip nat inside source list 1 interface FastEthernet0/1 overload

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Overall Rating: 5 (1 ratings)
Loading. Sat, 08/15/2009 - 07:53

debug ip nat

*Mar 1 03:30:30.703: NAT: translation failed (F), dropping packet s= d=

jaypower Sun, 08/16/2009 - 05:31

With GNS3, you can simply see NAT functioning by configuring a nat setup between two connected routers. The transport is your choice but I used FastEthernet for simplicity.

R0 - NAT router

int loop1

ip add

ip nat in


int f0/0

ip add

ip nat out


access-list 1 per host

ip nat inside source list 1 interface f0/0 over




Configure FastEthernet interface

int f0/0

ip add


Do a source ping from the loopback on the NAT router to the IP on R1 and view nat statistics and translations to see the attempt. Here is the output:

Router#ping source

Type escape sequence to abort.

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

Packet sent with a source address of


Success rate is 100 percent (5/5), round-trip min/avg/max = 4/8/12 ms

Router#sh ip nat stat

Total active translations: 1 (0 static, 1 dynamic; 1 extended)

Outside interfaces:


Inside interfaces:


Hits: 9 Misses: 1

Expired translations: 0

Dynamic mappings:

-- Inside Source

[Id: 1] access-list 1 interface FastEthernet0/0 refcount 1

Router#sh ip nat trans

Pro Inside global Inside local Outside local Outside global


You can do several scenarios and this is certainly not the only way to do it. However it will get you started and takes about <5 mins to set up.



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