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Duplicate ip addresses


I have a situation where I am receiving duplicate ip address notifications from a 7000 series router.  These are happening when I activate the outside interface on another router that has an outside interface ip address on the same subnet as the outside of the 7000 series router.  The duplicates are occurring on some of the static nat translated addresses that are configured on the 7000 series router. When I shut down the outside interface on the other router, and clear the arp cache on the 7000, then everything works fine.  The important point is that I have no static nat translations on the other router.  Certainly no translations – or configuration at all – of the reported duplicate addresses.  Since I have no translations or anything on the other router referencing these public addresses, what other items could be causing the duplications? 

2 Replies 2

Rich Uline


It would help if you could provide additional information. What does your topology look like? Also, you should have a log message on each device that is detecting the conflict. If you could post the details of those log messages from both routers, that would be helpful. The log message should look something like this:

Duplicate address sourced by aabb.ccdd.eeff


Nov 19 08:59:04.207: %IP-4-DUPADDR: Duplicate address x.x.x.18 on GigabitEthernet0/0, sourced by xxxx.xxxx.f5a4 .  F584 is the other isr.  The topology has the 7000 and other isr’s public in parallel linked to a switch and all behind an asa.  The 7000 and other isr’s are in parrallel.  The .18 public address is not defined on the other isr in any way. 

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