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DHCP relay and routing - help me with this scenario

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Miroslav Lukac
Occasional Contributor

DHCP relay and routing - help me with this scenario

I have following design in attachment(please see). Lets say there is ip routing enabled and dhcp-relay enabled on switch. VLAN 2,3 and 4 are only VLANs with IP, thus routing between them is enabled. Only VLAN2 is connected to port on ISA server.
Now questions:
1. Will PCs in VLANs 2,3 and 4 get the IP settings from DHCP?
2. If DHCP server is Win2003, is possible to get IP from 10.1.2.0/24 range for VLAN2, IP from 10.1.3.0/24 range for VLAN3 and so on? How to setup this on DHCP server?
3.Do I need some specific static routes?
4.If I do not want routing for VLAN5 (no IP assigned) but still need DHCP, do I need DHCP server in that VLAN?
5.Are the IP setting of all PC correct?

I will appreciate any help with this. Thanks.
3 REPLIES
Evert Goor
Trusted Contributor
Solution

Re: DHCP relay and routing - help me with this scenario

1. Yes if the isa server will allow dhcp requests

2. Yes . Just make multiple scopes on the dhcp server.

3 . Just def gateway for outside isa server should handle local routing to the dhcp server.

4. tricky one normaly you need an ip adress to get the swtich to forward the dhcp requests. so acl's are needed.

5. Looks good to me
Jeff Carrell
Honored Contributor

Re: DHCP relay and routing - help me with this scenario

replies to q's:

1) yes, if there are appropriate scopes setup for each subnet, see next q/a

2) you need multiple scopes on the dhcp server for each subnet:
scope 2 - 10.1.2.0/24, range for ip's, 10.1.2.2 g/w
scope 3 - 10.1.3.0/24, range for ip's, 10.1.3.2 g/w
scope 4 - 10.1.4.0/24, range for ip's, 10.1.4.2 g/w

3) well, you do need a static route in order to get to subnet 10.1.1.0, since that is where the dhcp server is, and the 4200 does not have 10.1.1.0 on it...and if you need to get off any vlans to the wan router for external access, then you'd need a static route in order to get off the 4200 switch...

i also assume you have routing enabled on the MS-ISA server...

4) in order to dhcp relay, you are required to have an ip addr on vlan5, but since you don't want routing on that vlan, then yes you will need a separate dhcp server for that vlan...(or separate NIC for vlan5 in the dhcp server and routing -not- enabled on that server)

5) they look basically ok...

hth...jeff
Miroslav Lukac
Occasional Contributor

Re: DHCP relay and routing - help me with this scenario

Thank You very much guys. I am facing such a scenario first time and it took me some time to do research on topic and I was unsure about some details. Thanks again.