[nsp] Duplicate Interface Addresses !!

[kevin gannon]

I spent the last three hours troubleshooting an EIGRP duplicate router 
ID issue.
The route cause was two interface on the same router with the same address.
Both interfaces were up/up and before the work started only one was up and
the duplicate address was then added to an already up/up address. To find
the duplicate address you need some hidden IOS command in EIGRP otherwise
I would still be looking !!!.

Anyone know why IOS only sometimes warns about this issue ?? You know
the warning you usually get:

kevin(config)#int loop 100
kevin(config-if)#ip address 10.10.10.1 255.255.255.0
10.10.10.0 overlaps with Ethernet0
kevin(config-if)#

I know its not isolated to one IOS revision as I have managed to
trick other IOS versions into creating this duplicate situation.

I have also spent hours troubleshooting MPLS problems due to
the same issue. Its madness !.

Regards,
Kevin