Vlan and DHCP

[Edward999]

HI i got problem getting ip address from my DHCP server on vlan port.

I have a Cisco 3550 core switch, 2 layer 2 Dell switch and a DHCP server.

My PC connected to one of my Dell switch and my DHCP server connected to another Dell switch. Both Dell switch and DHCP server having an ip address 192.168.1.X

DHCP connected to vlan1 port(Default vlan) having ip 192.168.1.X

I manage to get Ip address from DHCP when i connected to dell switch vlan1 (Default vlan).

When i connected to a port other then vlan1, i cannot get the ip address from the DHCP server.

Both of my 5324 Dell switch have tagging on port 24(SPF port), port 23 is having vlan1 and the rest of the port i created different vlan ID. My 3550 have trunking on the interface with 802.1q encapsulation.

interface GigabitEthernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
ip access-group 101 in

I already created the vlan at the 3550 global configuration mode and when i show vlan the vlan status is active and i already put in ip helper-address DHCP server. I also check the interface on 3550 is up and running.

interface Vlan101
ip address 10.1.22.1 255.255.255.0
ip helper-address 192.168.1.10

I also created a subnet 10.1.22.1 at my DHCP configuration file.

Please help...thx in advance

edward

 

[lambent]

Can you ping from the 3550 switch to the DHCP server (provided that you didn't block ping)?

Also what's in your access-list 101?

 

[Edward999]

Thanks for the reply. I can ping from my 3550 to DHCP and my access-list 101 is permit ip any any at my 3550

 

[Edward999]

ooops...sorry the vlan interface at 3550 is

interface Vlan101
ip address 10.0.1.1 255.255.255.0
ip helper-address 192.168.1.10

I also created a subnet 10.0.1.1 at my DHCP configuration file.

sorry for that.

many thanks for your reply.

 

[lambent]

Then try to hard code a static IP address 10.1.22.x in your PC with default gateway pointing to 10.1.22.1.

Plug the PC to the VLAN 101 ports in your Dell switches.

Check the L2 and L3 connectivity by pinging the default gateway and the DHCP server respectively.

 

[Edward999]

After i change to static ip 10.0.1.33, i can ping to default gateway 10.0.1.1 and i can ping to my 3550 192.168.1.X but i cannot ping to my DHCP server.


Is that mean that the traffic cannot go through my DHCP server. What should i do?

Please help.....

many thanks for your help.

 

[Edward999]

Hi I also cannot ping to my another layer 2 dell switch.

Is my vlan configuration at dell switch got problem?

thx

 

[lambent]

Check the default gateway of your DHCP server and see if it's set correctly.

Then ping from your DHCP server to the 192.168.1.x IP on the VLAN 1 interface (I suppose).

Then ping from your DHCP server to 10.0.1.1.

Then ping from your DHCP server to 10.0.1.33 which is the static IP of your PC right now.

 

[lambent]

You should have a "management VLAN" in each of your Dell L2 switch. Make sure that the Mgt VLAN has the proper subnet and the proper default gateway of that subnet.

 

[Edward999]

Hi thanks again for your reply.


I cannot ping to 10.0.1.1 and 10.0.1.33 from my DHCP server.

My DHCP default gateway point to one of my layer 2 dell switch.

Actually my PC point to another layer 2 dell switch.

thx

 

[Jsteve]

I'm not sure if your doing this, but make sure
- that everything in each vlan is in the same subnet
- point your dhcp to your vlan1 ip address on the 3550
- point your other pc on the second vlan to the vlan IP address and make sure that it's on the same subnet.
-make sure the ip helper-addres x.x.x.x (dhcp server address) is addred.

 

[lambent]

I assume your Dell switches are only layer-2 with no routing capability. So if you set the default gateway to the IP of the switches, the traffic destined to remote subnets will be terminated in those switches since they don't know the routes to remote subnets.

As per Jsteve suggestion, you'll have to set the default gateway to a router or a layer-3 device on the same subnet as your PC.

 

[Edward999]

Thanks a million guys that is the correct answer i'm looking for changing the DHCP default gateway.

I appreciate you help. Thanks again.

Edward