Interesting Dilema

[csharporbflat]

Here is my proposed configuration, tell me if I am missing something.

I have the following hypethetical subnetting scheme

2 subnets, 2 vlans.

lets say for argument that subnet 1 is on network 172.16.0.0

and subnet 2 is on netowkr 172.16.32.0

lets say of have 2 vlans

VLAN 10

VLAN 20

I have a router port IP assigned of 172.16.0.1

I have 2 DHCP pools that match the 2 subnets Im using

172.16.0.1 - 172.16.31.254 excluding 172.16.0.1

default gateway 172.16.0.1

and

172.16.32.1 - 172.16.63.254

default gateway 172.16.0.1

here is the issue.

both DHCP pools use the same default gateway as the switches can only be set up on the network to come off of a single port on the router

Now lets assume that all switches are Trunked and on the same VTP domain, and that all ports are set to VLAN 1.

Now some 5 or 6 switches down the line I have all of the ports assigned to VLAN 2,

This is wherer the problem arises

How will the router know Which DHCP pool to assign to wich VLAN. I want all hosts on this switch to be assigned to subnet 172.16.32.0. VLAN 2

and all hosts on all other switches to be assigned 172.16.0.0 on VLAN 1

How is this done?

.

What am I missing?

[Tom Watts]

Hi Drew,

The small business switches do not support VTP.

If using a L3 small business switch, you would enable DHCP option 82. specify the DHCP relay and then do add route on the DHCP server.

-Tom

[csharporbflat]

thanks for reply.

so if the small business switches dont support vtp, i can manually configure vlans on each switch

i would like to have dhcp comming from 1 central location , that being the router.

what is option 82 and is that set on the switch or router?

[Tom Watts]

The option 82 can be set on the switch. If your router is the DHCP server, it shouldn't require option 82 as long as the trunk/tags are understood.

-Tom