Hello,
I recently swapped out a 3650X for a 3560S. After connecting the 3650 to our network an issue occurred. Users started noticing that they could no longer print or access certain files. After verifying the IP address on the hosts, I noticed that they were receiving wrong information. Hosts were no longer receiving IP address from the closes 1, 2, or 3 DHCP servers but were receiving them from other remote sites. Since each remote site DHCP server only had scopes for their locations, users devices would no longer be on the same subnets as other devices. Exam: Site A is 172.20.X.X, Site B is 172.21.X.X, Site C is 172.22.X.X, etc.... Host from Site A would receive address from site B/C and B would also receive addresses from C.Regardless of the first 2 octets, if the 3 octets had the same value, addresses would cross networks. Exam: Vlan 5 (APs) from site A should be receiving 172.20.5.X address but they would receive 172.22.5.X addresses which also corresponded to a vlan 5 called APs.
To resolve the issue, I had to block off totally separate numbers for different locations. IE: vlan 1-5 for site A, vlan 6-10 for site b, 11-15 for site c. Site A became 172.20.1-5.X, Site B became 172.21.6-10.X, Site C became 172.22.11-15.X.
My question is do anyone know why all that occurred and what could be done to resolve the issue? I want to get it resolved for future admins. I would hate for someone to take over and use 172.21.1.X at site B and the network scrabbles again. Also, note that I configured dhcp pools on the 3650X and the same thing still occurred. As long as the one octet matches, IP addresses for that vlan will cross boundaries.
