Using DHCP across T1/routers 2

[SF18C]

Here is my set up

WAN link
|
SiteA SiteB
RouterA ----T1----RouterB----WAN Link
| |
| |
Layer3 Layer3
SwitchA SwitchB
| |
DHCP DHCP
ServerA ServerB
192.168.37.5 192.168.17.5
VLANs 30 to 41 VLANs 10 to 20




Situation: I currently have 2each WIN2K DHCP servers, one for each site with scopes created for the vlans at its location. I have layer3 switches that have the IP helper address for each vlan to that sites DHCP server. I have only about 10 vlans per site and I want to take down one of the DHCP servers (at siteB). Each VLAN contains 1 subnet (ie VLAN 30 is 192.168.30.X, VLAN 10 is 192.168.10.X). Each VLAN on the switch has an IP Helper for that sites DHCP server (i.e. for VLANs 30 -41 the IP helper-address is 192.168.37.5 and on VLANs 10-20 it is 192.168.17.5).


My questions
1. At site B do I put the IP helper on VLANS on SwitchB to DHCP server A (I don’t think this will do it)
2. Or do I need to set the IP helper for the vlans the DFGW to Router B and then place an IP helper on router B to DHCP server A ?
3. Do in need the IP helper on Router A as well?
4. Or is there another option I am totally blanking out.

The bottom line: How can I use 1 DHCP server across 2 routers and 2 layer three switches? I know it can be done…I just can’t get a PC at site B to find the DHCP server at site A. All past attempts die at Router B.

Thanks for any assistance…it’s late and I hope I an not missing something painfully obvious!


SF18C
CCNA, MCSE, A+, N+ & HPCC

"Tis better to die on your feet than live on your knees!"

 

[oj88]

You should put an ip helper-address command on every VLAN on your L-3 switches pointing to your DHCP server.

Also, it would help if you include the command ip forward-protocol udp bootpc. This will only allow DHCP requests to be forwarded by the router to the DHCP server. Otherwise, any broadcast traffic would be sent to the DHCP server unnecessarily by default.

Orlando Palomar Jr
CCIE# 11206, CCNP
CIPT Operations Specialist
Phil-Data Business Systems, Inc.

 

[Whoheard]

I agree with OJ88, but I would not put the Bootp forwarder on the router. The VLANS of the Layer 3 switches should be enough and are capable of directing DHCP broadcast traffic to the DHCP servers.

While your Layer 3 switch is configured with IP Helpers, so would the router; and this would create/generate duplicate DHCP requests from the same source. This would increase traffic flow across the WAN links--by a little bit.

Food for thought

bob

 

[oj88]

My apologies. I was indeed refering to adding the command on the L-3 switches. I unconsciously used the term "router" instead, as an L-3 switch is functionally equivalent to a router.

Bob is correct in saying that these commands must be configured on every VLAN on the L-3 switch... not on the WAN routers UNLESS, you have hosts connected on the network between the WAN router and the L-3 Switch.

Thanks for the clarification, Bob.

Orlando Palomar Jr
CCIE# 11206, CCNP
CIPT Operations Specialist
Phil-Data Business Systems, Inc.

 

[SF18C]

Thanks for the info...once we get the DHCP scopes copied from DHCP2 to DHCP1 I will see if I can get the clients to find the server.


SF18C
CCNA, MCSE, A+, N+ & HPCC

"Tis better to die on your feet than live on your knees!"