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How do I get DHCP to work on various Subnet VLANS using SBS 2003 Premium & Netgear FSM7352S

Posted on 2009-04-07
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Last Modified: 2013-11-30
I have a SBS 2003 Server and I need to introduce VLANS with 4 different Subnets

Server IP 192.168.1.200/24 LAN inside
Server IP 10.x.x.x WAN side
DHCP Scopes are set for each VLAN Subnet (see below)
Router in each scope is set to the VLAN IP (i.e. 192.168.x.1)
RIP 2 is enabled
bootpdhcphelper is enabled pointing to 192.168.1.200
VLAN Routing configured on Switch
VLAN 1 IP 192.168.1.1/24
VLAN 2 IP 192.168.2.1/24
VLAN 3 IP 192.168.3.1/24
VLAN 4 IP 192.168.4.1/24

Anyone have any idea why this doesnt work?

I have read SBS DHCP doesnt work with VLANS but then other sites say it works
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Question by:JAH227
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by:akalbfell
ID: 24090972
I dont know of any issue on SBS not supporting multiple DHCP Scopes so i will answer this as if thats not the issue...
under each vlan interface you should have the following...
ip broadcast-address x.x.x.x
ip helper-address y.y.y.y

where x.x.x.x = the broadcast address of that vlan
where y.y.y.y = is the address of the DNS server
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JAH227 earned 0 total points
ID: 24104590
I have found the solution! Unfortunately neither Microsoft or Netgear were of any help and there is no real documentation on the web.

The solution is as follows:

A Small Business Server is essentially a router itself.
It therefore stands to reason that there would need to be a static route entered on the SBS
In RRAS enter the Static Route as follows:
192.168.2.1/24 to 192.168.1.1 (This is the address of the port on the switch which is connected to the Server)
Continue to add the Static Routes for each VLAN.

Dont forget to set a default route on the switch to the Server: 0.0.0.0  0.0.0.0 192.168.1.200 (other wise the system doesnt know where to send packets that aren't on the LAN

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by:akalbfell
ID: 24107549
that doesnt make much sense. if your switch is L3 and doing routing what purpose does setting a static route to another network as the servers default gateway? if you could ping the server from another computer before than routing was working fine already.
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Author Comment

by:JAH227
ID: 24108472
An SBS server works as a router if it has 2 NICS
1 NIC inside (LAN)
1 NIC outside (WAN)
Simplisticaly:
A UDP Packet enters the LAN side requesting DHCP with the source 192.168.4.x
The server responds and sends the response back to 192.168.4.x
Only the thing is the NIC interface on the server is 192.168.1.200 (subnet 192.168.1.x/24)
So without a static route the packet would be routed through to 10.x.x.x because there is no reference to the subnet 192.168.4.x

Hope this explains it in understandable terms.

Familiarity with the FSM7352S is important - you cannot use iphelper for UDP 67 & 68, you have to use bootpdhcprelay. iphelper can be used for other ports. There is no reason to set broadcast address on the switch, the broadcast is changed to unicast which is sent through bootpdhcprelay to the SBS server (as stated in my question). iphelper to identify DNS is in the questioned scenario pretty irrelevant as this information is provided by the DHCP server in the response. Having said that it is possible on the switch to set up to 8 DNS Servers - but the solution works with these or without.

It isnt a CISCO switch! Nor is it a Nortel Switch - there are some differences and that isnt just the price!

The main bit (which I had missed, otherwise I wouldnt have posted the question) is that the SBS is acting as a router. Yes it was a Eureka moment when it came to me after a glass or two of fine Shiraz!

It works - and that is what I wanted!

If anyone who has both an SBS running VLANS using an FSM7352S and can show me a config that works (both switch and Server) that doesn't involve setting the stated static routes - please do so.
Otherwise I consider the matter closed and hope that this issue will assist others that may run into the same problem that I had initially. I havent found it documented anywhere else.







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