IP nat inside source list Command on CISCO Router/Switch

Command

IP nat inside source list

Use

This command is used to specify an access-list that matches which IPs should be translated.

Syntax

R1(config)#ip nat inside source list <access-list> <pool or interface> overload

Options

<pool> Specifies what NAT Pool to use.
<interface> Tells NAT to use the IP address on a given interface instead of a pool
<overload> Tells NAT to overload a single IP address so it can support numerous translations.

Example

In this example, we will remove all routing protocols on R2. Afer that, using NAT, we will restore reachbility so that R1 can ping 10.2.2.3

router eigrp 100
network 10.1.1.2 0.0.0.0
no auto-summary
router ospf 1
log-adjacency-changes
network 10.2.2.0 0.0.0.255 area 0
router rip
version 2
network 2.0.0.0
network 10.0.0.0
no auto-summary
R2(config-if)#no router rip
R2(config)#no router eigrp 100
R2(config-if)#no router ospf 1

R1(config)#ip route 0.0.0.0 0.0.0.0 10.1.1.2

R1(config)#do ping 10.2.2.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.2.2.3, timeout is 2 seconds:
…..
Success rate is 0 percent (0/5)

Now we will configure NAT using a pool of 10.2.2.5 to 10.2.2.10. Theses addresses will be assigned per session as needed by NAT.

R2(config)#access-list 10 permit 10.1.1.0 0.0.0.255
R2(config)#ip nat pool REACH 10.2.2.5 10.2.2.10 netmask 255.255.255.0
R2(config)#ip nat inside source list 10 pool REACH
R2(config)#int fa0/0
R2(config-if)#ip nat inside
R2(config-if)#int fa1/0
R2(config-if)#ip nat outside

R1(config)#do ping 10.2.2.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.2.2.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/39/116 ms

R2(config)#do sh ip nat trans
Pro Inside global Inside local Outside local Outside global
icmp 10.2.2.6:21 10.1.1.1:21 10.2.2.3:21 10.2.2.3:21
— 10.2.2.6 10.1.1.1 — —

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