RE: ISA Server as DHCP Server
- From: Shijaz <Shijaz@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 3 Aug 2006 07:03:02 -0700
- Since you have the DHCP Helper configured, devices on any VLAN can "send"
DHCP requests to your ISA machine.
- IMO you dont need a Default Gateway to have DHCP traffic sent to your
VLANs because the machines themselves dont have IP addresses yet, so can't
have packets "routed" (IP routing) to them. Remember, the workstation that
was booting doesn't know who it is, and only has its MAC address already
assigned.
What a IP Helper does is that it sniffs DHCP requests from the network and
forwards it to the preset DHCP server (ISA machine) by placing the device's
own IP as the SOURCE IP or by using Gateway Interface Address (GIADDR) field
on the request. The DHCP server will then return the IP to this device and
the device in turn forwards it to the original requesting workstation.
--
Shijaz
MCSE:Security, CCNA
www.shijaz.com/isaserver
"Heath" wrote:
We have that IP Helper Address Configured on those other devices. If we run.
DHCP on any other server, it works perfectly, but ISA will only answer
requests from the same VLAN as the internal adapter. How does it know how to
route internally among VLANs without a default gateway on that adapter? I
set this up EXACTLY as the deployment guide suggests including the creation
of the rules to allow DHCP Server and Relay.
"Shijaz" wrote:
To use a DHCP Server to service multiple VLANs you need to use a feature
called "DHCP Helper IP address" on the device that you use to route between
your VLANs.
For more info, see this article:
http://tcpmag.com/qanda/article.asp?EditorialsID=285
For information on installing DHCP on ISA 2004, see
http://www.microsoft.com/technet/prodtechnol/isa/2004/plan/isaondhcpserver.mspx
--
Shijaz
MCSE:Security, CCNA
www.shijaz.com/isaserver
"Heath" wrote:
I've installed an ISA server with two network cards as a firewall/proxy for a
mid-size business. One adapter has a live internet address (External
Network) and one has an internal address (Internal Network). The deployment
document located at the ISA TechCenter tells me to only have a default
gateway on the external network adapter. All is fine and well with that.
The document also tells me to use the ISA Server as my DHCP server and to
disable my current DHCP Server. So I have created all my scopes on the ISA
Server and it is now my DHCP Server. With the default gateway set only on
the external network, it doesn't respond to DHCP requests from other VLANs.
Also if you ping it from the same network as the internal adapter, it
responds, but if you ping it from another VLAN, you get no response. How can
I use this as my DHCP server if it doesn't know how to route between VLANs on
my internal network?
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