dhcp request being nak'd by 3650 after receiving request

[slichtblau]

Hello,

  I am using a 3650 as a dhcp server for several vlans and any client that attempts to get a dhcp address receives a nak from the 3650.  I have a base configuration attached, as well as a png of the wireshark capture showing base info seen.  Is there some default configuration on this hardware that disable the dhcp functionality, I am using IOS 16.8.1a, and had the same result with 16.6.4.  The same dhcp configuration seems to work fine on a 3850.  Or is there some needed configuration that I am missing?!

Thanks,

Scott.

[Georg Pauwen]

Hello,

the default router IP addresses configured in the DHCP pools and the addresses configured on the actual VLAN interfaces do not match. Also, Vlan 101 has a wrong subnet mask configured:

ip dhcp pool dl-101
network 172.16.0.0 255.255.248.0
default-router 172.16.0.1
dns-server 8.8.8.8
lease 0 2
!
ip dhcp pool emn-301
network 192.168.31.0 255.255.255.0
default-router 192.168.31.1
dns-server 8.8.8.8
!
ip dhcp pool clr-501
network 192.168.51.0 255.255.255.0
default-router 192.168.51.1
dns-server 8.8.8.8
lease 0 2

interface Vlan101
ip address 172.16.0.5 255.255.255.248
no ip route-cache
!
interface Vlan301
ip address 192.168.31.5 255.255.255.0
no ip route-cache
!
interface Vlan501
ip address 192.168.51.5 255.255.255.0
no ip route-cache

Change it to:

interface Vlan101
ip address 172.16.0.1 255.255.248.0
no ip route-cache
!
interface Vlan301
ip address 192.168.31.1 255.255.255.0
no ip route-cache
!
interface Vlan501
ip address 192.168.51.1 255.255.255.0
no ip route-cache

[chrihussey · Accepted solution]

Take another look at the mask on the Vlan101 interface:

!
interface Vlan101
 ip address 172.16.0.5 255.255.255.248
 no ip route-cache
!

should be 255.255.248.0.

Also, i just noticed this,  take a second look at the excluded addresses for:

!

ip dhcp excluded-address 192.168.5.1 192.168.51.10
ip dhcp excluded-address 192.168.5.250 192.168.51.254

!

Regards

[slichtblau · Accepted solution]

Thank you much, that was exactly IT!    Since none of the dhcp scopes worked, I was only troubleshooting the 172.16.0.0/21 one, but the exclude on 192.168.5...  disabled everything on the other 2 scopes.  Always good to get a second set of eyes - very much appreciated!!

-Scott.