DHCP Server in multiple VLANs

[verdura]

Hi,

I have a layer 3 switch (SG500) and I created VLANs in it. 

I have a Microsoft DHCP server that I need to serve all my VLANs. When I plug in a PC in VLAN110 I cannot get addresses. If I put it in VLAN120 all works fine.

Part of the config is:

vlan database
vlan 10,100,110,120
exit
!
ip dhcp relay address 192.168.200.1
ip dhcp relay enable
ip dhcp information option
!
interface vlan 100
 name STUDENTS
 ip address 192.168.100.50 255.255.255.0
 ip dhcp relay enable
!
interface vlan 110
 name STAFF
 ip address 192.168.110.50 255.255.255.0
 ip dhcp relay enable
!
interface vlan 120
 name SERVERS
 ip address 192.168.200.50 255.255.255.0
!
interface gigabitethernet1/1/16
 description "PC1"
 ip source-guard
 switchport mode access
 switchport access vlan 120
!
interface gigabitethernet1/1/17
 description "PC2"
 ip source-guard
 switchport mode access
 switchport access vlan 110
!
interface gigabitethernet1/1/21
 description "DHCP SERVER"
 ip dhcp snooping trust
 switchport mode access
 switchport access vlan 120
!
macro auto processing type host enabled
ip dhcp snooping
ip dhcp snooping information option allowed-untrusted
ip dhcp snooping vlan 100
ip dhcp snooping vlan 110
ip source-guard
ip default-gateway 192.168.200.254

I plug in a PC in gigabitethernet1/1/17 and I cannot get address.

Is there any command to see the DCHP requests?

Can you please help me?

Thanks

[ktonev]

Hi,

There is no command to see DHCP requests - you can do port mirroring on this port and have another port connected to a PC running Wireshark. This way you will be able to see all packets, DHCP negotiation, etc.

Have you tried to plug another PC/device in port 17?

Have you tried to configure another port in VLAN110 and see if you can receive an IP address?

[verdura]

Thanks for the answer. 

I've  been overwhelmed with work and cannot do more tests. Probably next week I'll try again.

Thanks for the idea of port mirroring /Wireshark. I'll try it!

[johndesgarennes]

If you have dhcp snooping enabled you can do a "show ip dhcp-snooping binding" to see the dhcp snooping database. I also believe you need to enable Ip arp inspection if you want to enable dhcp snooping.

[verdura]

I had a problem in DHCP server...
All works fine now!