Admin: New page: ==WHAT== The simplest way to learn some cisco is trying to do a simple NAT in your home router so you can share your internet connection multiple computers. This is probably the most aske...

2009-06-25T19:32:47Z

New page: ==WHAT== The simplest way to learn some cisco is trying to do a simple NAT in your home router so you can share your internet connection multiple computers. This is probably the most aske...

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==WHAT==

The simplest way to learn some cisco is trying to do a simple NAT in your home router so you can share your internet connection multiple computers. This is probably the most asked question by beginners.

==STEP 1 - Gateway==

Get into configuration mode
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Set the hostname so we don't get confused
Router(config)#hostname gateway
And configure the fa0/0 interface as the inside nat network
gateway(config)#interface FastEthernet 0/0
gateway(config-if)#ip nat inside
gateway(config-if)#ip address 192.168.0.1 255.255.255.0
gateway(config-if)#no shutdown
*Mar 1 00:18:38.071: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Mar 1 00:18:39.071: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
gateway(config-if)#exit
Same thing for 1/0, outside nat ( our Inet connection )
gateway(config)#interface FastEthernet 1/0
gateway(config-if)#ip nat outside
gateway(config-if)#ip address 10.0.0.3 255.255.255.0
gateway(config-if)#no shutdown
*Mar 1 00:18:40.011: %LINK-3-UPDOWN: Interface FastEthernet1/0, changed state to up
*Mar 1 00:18:40.013: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0, changed state to up
gateway(config-if)#exit
Now set up a standard accesslist with the name 'inside_nat_addresses' ( feel free to change it ) in which we tell that 192.168.*.* will match this ACL
gateway(config-if)#ip access-list standard inside_nat_addresses
gateway(config-std-nacl)#permit 192.168.0.0 0.0.0.255
gateway(config-std-nacl)#exit
NOW, GOD says to do NAT ! This is read "I want to nat from _inside out_ all the hosts in 'inside_nat_addresses' to fa1/0 with port forwarding
gateway(config)#ip nat inside source list inside_nat_addresses interface FastEthernet 1/0 overload
gateway(config)#exit
*Mar 1 00:18:56.083: %SYS-5-CONFIG_I: Configured from console by console
SAVE it and pray it works ! ( WORKED FOR ME !
gateway#write mem
Building configuration...
[OK]
==STEP 2 - Client==

Now 1 of the clients .. I'll be using another router as a client ( cisco again )
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Set the hostname so we don't get confused
Router(config)#hostname test
And configure the fa0/0 interface as one ip in our NAT network
test(config)#interface FastEthernet 0/0
test(config-if)#ip address 192.168.0.5 255.255.255.0
test(config-if)#no shutdown
*Mar 1 00:20:11.051: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Mar 1 00:20:12.061: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
test(config-if)#exit
Now add the default gateway
test(config)#ip route 0.0.0.0 0.0.0.0 192.168.0.1
test(config)#exit
Et voila !
test#write mem
Building configuration...
[OK]

==DEBUGGING==

Now you should be able to NAT all your 192.168.*.* to your fa1/0

Check the current settings using
show ip interface brief
and the nat connections
show ip nat translations

Some debugging
debug ip packet detail
and
debug ip nat detail
Be careful with the debug levels, 'detail' is only recommended in lab situations !

When trying to use pings, to stop them use ctrl+shift+6

[[Category: Cisco]]
[[Category: NAT]]

Cisco Simple NAT - Revision history

Admin: New page: ==WHAT== The simplest way to learn some cisco is trying to do a simple NAT in your home router so you can share your internet connection multiple computers. This is probably the most aske...