[nsp] Doing a duplicate IP address to changeover default gateway gear

[Goldberg Alain (IT)]

My problem goes like this:
 
I'v got an old overloaded and crashing 5500 ios/catos, which should be
replaced by two brand-new 65xx/Sup720.
I can't afford a down-time.
 
The simplest is probably to use HSRP, but I would like to avoid it for
two reasons:
1) I am not confident that the 5500 will handle the configuration change
(Yes ... THIS bad !)
2) The 5500 is running Decnet (and I will not run Decnet on the 65xx's),
thus the MAC address is a Decnet mac-address,
   so even if I could carry over this mac-address with HSRP i wouldn't
like to.
 
So I had this idea, and would like to hear your comments:
The 5500 and 65xx's are layer-2 trunk connected - same domain, and both
run EIGRP.
Assuming default gateway of VLAN-2 is: 192.168.1.1 , curently on 5500
interface VLAN-2.
 
I'll set the VLAN-2 IP address of the 65xx to 192.168.1.1 <<---
duplicate IP
 
and one second later the I'll set the VLAN-2 IP address of the 5500 to
192.168.1.254
 
What can go wrong ?
 
Am I rigth to assume that old computers that will not notice the ARP
change will continue to send datagrams
 to the MAC address of the 5500 which now has the 192.168.1.254 IP, and
that the 5500 will route the packets ?
 
( The 5500 is curently the default gateway of over 1000 hosts on several
VLAN's/subnets)
 
Thanks for any reaction ;-) either positive or negative.
 
 
 Regards,
___________________________________________________________
Alain Goldberg - Network manager - CCDA/CCNA AGG-RIPE
Tower              Semiconductors           LTD.
Tel : 972-4-6506003        Fax : 972-4-6547788        Cell:
972-64-209662