NAT causes duplicate I.P

Answered Question
Nov 1st, 2008

I have a strange problem. We have nat setup on our gig 0/0 interface. You would think that it wouldn't create an arp entry for the natted I.P since its being done inside. However, it seems that for some reason, the nat I.P we are using is being advertise between both routers and they are complaining about duplicate I.P. Is this a bug? Not sure how to resolve this issue.

thx.

Here are some of the outputs I'm seeing.

il400s02hwr02#show version

Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.4(8c), RELEASE SOFTWARE (fc3)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2006 by Cisco Systems, Inc.

Compiled Tue 12-Dec-06 02:09 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

il400s02hwr02 uptime is 36 weeks, 6 days, 47 minutes

System returned to ROM by power-on

System restarted at 08:47:27 EST Sun Feb 17 2008

System image file is "flash:c3845-advipservicesk9-mz.124-8c.bin"

This product contains cryptographic features and is subject to United

States and local country laws governing import, export, transfer and

use. Delivery of Cisco cryptographic products does not imply

third-party authority to import, export, distribute or use encryption.

Importers, exporters, distributors and users are responsible for

compliance with U.S. and local country laws. By using this product you

agree to comply with applicable laws and regulations. If you are unable

to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

http://www.cisco.com/wwl/export/crypto/tool/stqrg.html

If you require further assistance please contact us by sending email to

[email protected].

Cisco 3845 (revision 1.0) with 484352K/39936K bytes of memory.

Processor board ID FTX1133A3UZ

2 Gigabit Ethernet interfaces

1 Serial interface

1 Virtual Private Network (VPN) Module

1 Subrate T3/E3 port

DRAM configuration is 64 bits wide with parity enabled.

479K bytes of NVRAM.

125440K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2102

---------------

Nov 1 10:40:37.798 EST: %IP-4-DUPADDR: Duplicate address 10.154.31.47 on GigabitEthernet0/0, sourced by 001d.46c7.8250

Nov 1 10:41:07.799 EST: %IP-4-DUPADDR: Duplicate address 10.154.31.93 on GigabitEthernet0/0, sourced by 001d.46c7.8250

Nov 1 10:41:37.800 EST: %IP-4-DUPADDR: Duplicate address 10.154.31.25 on GigabitEthernet0/0, sourced by 001d.46c7.8250

Nov 1 10:42:07.800 EST: %IP-4-DUPADDR: Duplicate address 10.154.31.71 on GigabitEthernet0/0, sourced by 001d.46c7.8250

Nov 1 10:42:37.801 EST: %IP-4-DUPADDR: Duplicate address 10.154.31.8 on GigabitEthernet0/0, sourced by 001d.46c7.8250

il400s02hwr02#

il400s02hwr02#show running-config interface gigabitEthernet 0/0

Building configuration...

Current configuration : 268 bytes

!

interface GigabitEthernet0/0

description CBOE_RTR1

ip address 10.154.31.2 255.255.255.0 secondary

ip address 192.168.86.168 255.255.255.240

ip access-group 100 in

ip nat inside

ip virtual-reassembly

duplex auto

speed auto

media-type rj45

no keepalive

end

ip nat inside source static 170.137.48.32 10.154.31.5

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 8 years 2 months ago

Hello Bedevere,

have you configured stateful NAT on the two C3845 ?

see

http://www.cisco.com/en/US/docs/ios/ipaddr/configuration/guide/iadnat_cfg_ha_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1053349

This can be helpful

Hope to help

Giuseppe

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Loading.
bedevere.curry Wed, 11/05/2008 - 10:32

Thanks. We will try it this weekend since we can't make any changes to it during the weekday.

Actions

This Discussion