DHCP not working

[garynicklaw]

DHCP

I have a cisco 2921 router connected to a cisco sg300-52 L3  switch. The switch is configured with several subnets and I need to use  the router for DHCP. I setup DHCP on the router to assign addresses to a  subnet on the switch but cannot get it to work.

Router:

gateway to LAN is xxx.16.10.1

ip dhcp excluded-address xxx.16.0.1 xxx.16.0.9

!

ip dhcp pool data

network xxx.16.0.0 255.255.254.0

default-router xxx.16.1.1

dns-server xxx.16.1.202

domain-name mydhcp.com

Switch to router xxx.16.10.2

Network on switch for DHCP is xxx.16.1.1

when I do a sho dhcp spool I see the addresses

any idea?

[David Hornstein]

Hi Gary,

I am wondering if you need to vlan and trunk your ethernet interface going to the SG300 switch?

See a example i used on my old 2821 router;  usually on my 300 series switch I leave vlan1 untagged and leave vlan 100 tagged on my trunk port.

Here is my router config , notice that I tagged the interfaces going to my ethernet switch. Works ok.

GigabitEthernet0/1 is the interface trunked to my switch.

ip dhcp excluded-address 192.168.20.1 192.168.20.10

ip dhcp excluded-address 10.2.1.1 10.2.1.10

!

ip dhcp pool data

   import all

   network 192.168.20.0 255.255.255.0

   default-router 192.168.20.1

   dns-server 209.18.47.61 209.18.47.62

!

ip dhcp pool Voice

   network 10.2.1.0 255.255.255.0

   dns-server 209.18.47.61 209.18.47.62

   default-router 10.2.1.1

interface GigabitEthernet0/1

no ip address

duplex auto

speed auto

!

interface GigabitEthernet0/1.1

encapsulation dot1Q 1 native

ip address 192.168.20.1 255.255.255.0

ip virtual-reassembly in

!

interface GigabitEthernet0/1.100

encapsulation dot1Q 100

ip address 10.2.1.1 255.255.255.0

hope this helps

regards Dave

[garynicklaw]

David,

Thanks for the response. When I finally found where to download the sg300 maintenance manual I found where I needed to setup the switch as a DHCP relay for the various subnets on the switch.

Thanks

[garynicklaw]

David,

What does the “import all” command do in the DHCP?

[David Hornstein]

Hi Gary,

My config assumes that the Sx300 series switch is trunked to the router.  I guess you are just relaying dhcp requests via vlan1 to a router. 

Import all does the following,  it  imports Dynamic Host Configuration Protocol option parameters into the DHCP server database.

regards Dave

[garynicklaw]

David,

Thanks, I was reading up on that. Last thing is to setup the Firewall in the 2921 router, any examples on that?

Thanks