DHCP issue on Cisco 3650 switch

[M Talha]

Dear All,

I have been facing an issue where users complains of not getting an IP address from DHCP server although i have done all the necessary configuration and checked multiple times. I am using 3650 switch with built in wireless controller for my three AP's. Using a pool of 192.168.1.0/26 and using option 43 and 66 for wireless users. Using lease time of 24 hrs but still getting problem. Users that have been assigned static IP's works fine but rest of the users still facing problem on daily basis. Need your help guys. Thanks

[Reza Sharifi]

Hi,

Can you post switch config?

[M Talha]

Please find the attached config file. Sorry for late reply.

[surahuja]

Hi , 

The official CISCO document states that option 43 is declared via either ascii or hex values comma-separated. The manner in which the hex value is to be calculated is given as : 

"Note: TLV values for the Option 43 suboption: Type + Length + Value. Type is always the suboption code 0xf1. Length is the number of controller management IP addresses times 4 in hex. Value is the IP address of the controller listed sequentially in hex. For example, suppose there are two controllers with management interface IP addresses, 192.168.10.5 and 192.168.10.20. The type is 0xf1. The length is 2 * 4 = 8 = 0x08. The IP addresses translates to c0a80a05 (192.168.10.5) and c0a80a14 (192.168.10.20). When the string is assembled, it yields f108c0a80a05c0a80a14. The Cisco IOS command that is added to the DHCP scope is option 43 hex f108c0a80a05c0a80a14."

http://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html

Is the manner in which you have put this value in your configuration correct ?

Also, do you have another upstream device whose address is X.Y.Z.65 ? The config you provided marks the vlan1 IP as 66 and I suppose you are carrying all the network traffic on vlan 1 itself. 

ip dhcp pool Servers
 network X.Y.Z.64 255.255.255.192
 default-router X.Y.Z.65 
 dns-server X.Y.Z.25 X.Y.Z.43 
 option 43 hex f104.8ce7.ae42
 option 66 ip X.Y.Z.61 
 lease 365
!

[M Talha]

No i haven't any upstream device with ip address X.Y.Z.65. Secondly i have correctly converted the ip address X.Y.Z.66 (vlan ip) in the hex with option 43 in DHCP configuration with manner as described by you and the Cisco documentation. Still issue exist.

[surahuja]

Hi , 

66 seems to be the switch IP. However, you will be accepting option 43 set packets from the APs. So the hex value is calculated for the range of AP IPs. The process to do that is mentioned in the document attached above. 

If that does not help , can you try without the options and see if that works ?

Regards,