IPv6 duplicate address detection on a Cisco 1841 router

[dadamsjrsnoopy]

I am working with real hardware, going through a Cisco book on IPv6.  I set up three routers.  R1 and R2 are connected fa0/1 to fa0/1.  When I configure the interfaces with distinct linked local addresses or global unicast addresses, I can ping between the two.  When I deliberately set either the LLA or GUA on one of them to be a duplicate of the other router's IPv6 address, I get the "duplicate address" error on that device.  But not on the other device.  Then, no matter what I do, change the address back so it isn't a duplicate, change the address on the other router to a different address, remove the addresses off of the other router so there are no addresses on the fa0/1 interface, shut down then turn the other interface back on, the error on the router I configured the duplicate address continues to have that error until I reload it.  I have waited even over an hour before reloading the router.  So my question is, is that how it is supposed to be - the error stays even if the duplicate address is removed, until I reload the router?

Thank you,

David Adams, Mobile, AL

[Harold Ritter]

Hi David,

>  When I deliberately set either the LLA or GUA on one of them to be a duplicate of the other router's IPv6 address, I get

> the "duplicate address" error on that device. But not on the other device. 

This is normal behavior. The newly configured device does the DAD and reports the duplicate address. The other device does not need to do anything, since it already owns the IPv6 address.

> Then, no matter what I do, change the address back so it isn't a duplicate, change the address on the other router to a

> different address, remove the addresses off of the other router so there are no addresses on the fa0/1 interface, shut

> down then turn the other interface back on, the error on the router I configured the duplicate address continues to have > that error until I reload it.

This is not normal behavior. Replacing the duplicate IPv6 address should be enough to stop the duplicate address notification.

Regards,