03-08-2017 01:17 PM - edited 03-08-2019 09:40 AM
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.
03-08-2017 01:28 PM
Hi
Are you running routing protocols on this devices? have you configured the Ip helper-address under the SVI?
Could you please provide the config or diagram?
Thank you in advance.
03-08-2017 01:54 PM
Yes, I am currently using it to route traffic. I only have one default static entry (0.0.0.0 0.0.0.0 10.91.16.1). Also, ip helper-address is configured on the SVI. The biggest problem with the entire issue is, that once I replaced the 3560 at one remote center, IP addresses at 3 other locations started changing.
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide