John Neiberger wrote: > > I'm planning on moving routing responsibilities from a router to our > 6513 and I *really* need to minimize downtime. I'll be moving an > interface IP address from one device to another and this is the default > gateway for all devices on that network. The problem is that all > devices on that subnet will have the wrong MAC address in their ARP > caches. I know that if I issue a unicast ping from the new router it > will force the end host to update its ARP cache but a broadcast ping > does not accomplish the same thing, probably because most devices ignore > a broadcast ping, and I don't feel like pinging every device > individually. > > I can't configure HSRP just to gain the benefit of gratuitous ARP; > simply configuring it will be disruptive and that's what I'm trying to > avoid. > With the new box being a Cisco, the good answer is you won't have to do anything. For many many years, Cisco routers have performed several operations anytime you "no shut" an interface or change its IP address: 1) ARP broadcast as a duplicate IP address test (and hope nobody replies). 2) Gratuitous ARP reply sent to the broadcast MAC. The latter causes every local host to blindly overwrite its previous ARP entry. Life goes on undisturbed... If you want to observe this behavior without a protocol analyzer, type "debug arp", then perform the change.
Marty Adkins Email: [EMAIL PROTECTED] Chesapeake NetCraftsmen, LLC o:410.757.3050, p:[EMAIL PROTECTED] 1290 Bay Dale Drive, Suite 312 http://www.netcraftsmen.NET Arnold, MD 21012-2325 Cisco CCIE #1289 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51692&t=51674 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
