NAT for overlapping networks

October 25, 2008 at 11:36 am | Posted in IP Services, NAT | Leave a comment

IEWB1 v5 Task 13.25

R1 and R2 both have a new loopback1 with IP address of 10.0.0.0/24. Configure R1 so that R2 can access R1 loopback using IP of 11.0.0.0/24, while that traffic from R2 appear to R1 as from 22.0.0.0/24 subnet.

 

Configuration

Rack1R1#sh run | in interface|nat|ip route

interface Loopback1
 ip add 10.0.0.1 255.255.255.0
 ip nat inside
interface Serial0/0
 ip nat outside
interface Serial0/1
 ip nat outside

router rip
 network 11.0.0.0

ip route 11.0.0.0 255.255.255.0 Null0
ip route 22.0.0.0 255.255.255.0 Serial0/1

ip nat pool R2_LOOP1_POOL 22.0.0.1 22.0.0.254 prefix-length 24
ip nat inside source static network 10.0.0.0 11.0.0.0 /24
ip nat outside source list R2_LOOP1_REAL pool R2_LOOP1_POOL

 

Debugging

See a debugging sample when there’s a typo mistake in the NAT POOL
ip nat outside source list R2_LOOP1_REAL pool R2_LOO1_POOL
Rack1R1#debug ip nat detailed

*Mar  1 01:12:35.771: NAT: alloc — pool R2_LOO1_POOL not found
*Mar  1 01:12:35.775: NAT: failed to allocate address for 10.0.0.2, list/map R2_LOOP1_REAL
*Mar  1 01:12:35.775: NAT*: o: icmp (10.0.0.2, 11) -> (11.0.0.1, 11) [44]    
*Mar  1 01:12:35.775: NAT*: o: icmp (10.0.0.2, 11) -> (11.0.0.1, 11) [44]
*Mar  1 01:12:35.775: NAT*: s=10.0.0.2, d=11.0.0.1->10.0.0.1 [44]
*Mar  1 01:12:35.775: NAT: alloc — pool R2_LOO1_POOL not found
*Mar  1 01:12:35.779: NAT: failed to allocate address for 10.0.0.1, list/map R2_LOOP1_REAL
*Mar  1 01:12:35.779: NAT: translation failed (L), dropping packet s=10.0.0.1 d=10.0.0.2
no ip nat outside source list R2_LOOP1_REAL pool R2_LOO1_POOL
ip nat outside source list R2_LOOP1_REAL pool R2_LOOP1_POOL

Rack1R1#
*Mar  1 01:17:36.987: NAT*: o: icmp (10.0.0.2, 13) -> (11.0.0.1, 13) [46]    
*Mar  1 01:17:36.987: NAT*: o: icmp (10.0.0.2, 13) -> (11.0.0.1, 13) [46]
*Mar  1 01:17:36.991: NAT*: s=10.0.0.2->22.0.0.1, d=11.0.0.1 [46]
*Mar  1 01:17:36.991: NAT*: s=22.0.0.1, d=11.0.0.1->10.0.0.1 [46]
*Mar  1 01:17:36.991: NAT: i: icmp (10.0.0.1, 13) -> (22.0.0.1, 13) [46]    
*Mar  1 01:17:36.991: NAT: s=10.0.0.1->11.0.0.1, d=22.0.0.1 [46]
*Mar  1 01:17:36.991: NAT: s=11.0.0.1, d=22.0.0.1->10.0.0.2 [46]
Doc CD Navigation

  • Cisco IOS IP Addressing Services Configuration Guide, Release 12.4
  • Part 6: NAT
  • Configuring NAT for IP Address Conservation
  • Configuration Examples for Configuring NAT for IP Address Conservation
  • Allowing Overlapping Networks to Communicate Using NAT

 or

  • Translating Overlapping Address: Example
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