Media for Cisco SLB: Duplicate Address

Cisco SLB: Duplicate Address

I have a Cisco 3640 (IOS 12.4.12) where I have configured SLB to load balance two apache servers.

Here is a configuration extract (I have replaced real IPs with letters):

ip slb serverfarm WEBFARM real x.y.z.A faildetect numconns 3 numclients 1 retry 180 inservice real x.y.z.B faildetect numconns 3 numclients 1 retry 180 inservice

ip slb vserver VIRT_TCP_00 virtual x.y.z.C tcp 0 serverfarm WEBFARM idle 600 inservice ! ip slb vserver VIRT_UDP_00 virtual x.y.z.C udp 0 serverfarm WEBFARM idle 600 inservice !

formatting link

will resolve to x.y.z.C

real hosts A and B have

ifconfig lo:1 x.y.z.C netmask 255.255.255.255

In theory the router shoud learn which mac addresses A and B have and forwards packets for x.y.z.C to either A or B

However, it appears that sometimes it complains as follows:

Dec 18 00:20:00 router 316: 000322: Dec 18 00:20:00.082 GMT: %IP-4-DUPADDR: Duplicate address x.y.z.C on BVI1, sourced by

0010.1010.1001

0010.1010.1001 is the mac address that belongs to x.y.z.B

the message varies reporting either A or B.

Has anyone else had a similar problem with SLB? How do I resolve this issue?