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.
Here are some of the outputs I'm seeing.
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:
If you require further assistance please contact us by sending email to
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#show running-config interface gigabitEthernet 0/0
Current configuration : 268 bytes
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 nat inside source static 188.8.131.52 10.154.31.5
have you configured stateful NAT on the two C3845 ?
This can be helpful
Hope to help