70-216 - DHCP Relay Agent..Where does it go?

Author

DHCP Relay Agent..Where does it go?

River19

2002-07-30, 4:57 pm

Okay, obviously if anyone has taken the beast they know that Microsoft likes to use the DHCP Relay agent alot in this exam. I do know WHAT the DHCP Relay agent does, but what I don't know is how to use it. More specifically, where to put it when designing a network.

For example, suppose I have two subnets, Subnet A and Subnet B.

Subnet A has 200 clients and a DHCP server local to the subnet.

Subnet B has the same amount of clients, but no DCHP server. These two subnets are connected by a router which does not support the forwarding of BOOTP packets. The DHCP server has active scopes installed for each subnet.

This is the typical setup for a DHCP relay question. Now what I want to know is, where do I install the DHCP relay agent?? Would it be on a computer on subnet A? subnet B? the server? the router?

I really got spanked on this one when I took the test and failed so I'm trying to improve on what I missed. Any help would be great.

Sexy Lexy

2002-07-30, 5:32 pm

DHCP relay agents provide IP addresses for clients on different subnets that do not have their own DHCP server and are segmented by routers.

If you have two subnets (A and B) with a DHCP server on A the the relay agent is placed on a server in subnet B as subnet A relays requests (Passes requests) over to the server on subnet B. Thus providing clients in B with an IP address and respective IP information.

You can also install a relay agent on an RRAS server to enable access to other segments on the network besides the one on which the RRAS server is located.

You don't need to install the Microsoft DHCP relay agent on a DHCP server or on a router. You will find that relay agents are designed for routed networks where the router does not forward DHCP requests. As the DHCP server already issues IP addresses you don't need one on a DHCP server.

Hope this helps.

Pavlov

2002-07-30, 5:34 pm

You would install the DHCP Relay Agent on Subnet B.

For each IP network segment that contains DHCP clients, either a DHCP server or a computer acting as a DHCP relay agent is required.

Somebody feel free to correct me if I'm wrong on my interpretation here.

Slinky

2002-07-30, 6:42 pm

quote:
Originally posted by Pavlov
You would install the DHCP Relay Agent on Subnet B.

You are correct. The relay agent basically listens for DHCP requests from client computers and forwards those requests to a DHCP server. Again you only need this when you dont have an rfc 1542 compliant router. When taking the tests its important that you catch that little keyword. It can make the difference between passing or failing.

River19

2002-07-30, 9:07 pm

Thanks guys, your comments are definately appreciated.

Thanks Sexy Lexy for clearing that up.

River19

2002-07-31, 2:00 pm

One more thing before I lay this whole DHCP Relay agent thing to rest, do you install it on a server on Subnet B or on a workstation? Or does it matter?

Sexy Lexy

2002-07-31, 2:03 pm

Relay agents are installed on the server, to my knowledge you can't install it on a Windows 2000 professional computer (Unless there is an add-on to do it)

Napsterbum

2002-07-31, 11:13 pm

Sweet, these boards are awesome, i cant wait till im a 2k Mcsa... great thing about it, im not even 16

Zaraspook

2002-08-01, 11:28 pm

In the context of Windows 2000 only, the DHCP relay agent service is only available via the Windows 2000 server product configured through the RRAS console.

A DHCP relay agent acts as an agent for the DHCP server, listening on the local segment where no DHCP server is located for any DHCP/BOOTP broadcast requests. Once a client broadcasts a request for an IP address, the DHCP relay agent hears the broadcast and relays this request via a directed send, (point to point), to the DHCP server located on the other segment. No broadcasts are used for that communication, since the DHCP relay agent and the DHCP server are both located on different subnets. The DHCP server then responds to the request by issuing an IP address assignment to the DHCP relay agent, (again via a directed send), which in turn relays the address to the client.

The DHCP server uses two separate scopes, one for the local segment that the DHCP server is located on and the other for the network segment that the DHCP relay agent is located on. The DHCP server can tell the difference between the clients that request addresses on the local subnet, (DHCPDISCOVER broadcast), and the requests for addresses by a DHCP relay agent, (IP address and subnet mask of the DHCP relay agent is included with the request so the DHCP server can distinguish the network ID). The addresses are then assigned accordingly, based on the subnet of the requesting machine.

You should never install the DHCP relay agent on a server running the DHCP service. Also, you should never place a DHCP relay agent on the same physical network segment where a DHCP server is located. You should instead always place a DHCP relay agent on a server located on the same physical network segment as the clients it is intended to service, where no DHCP server is located.

Sexy Lexy

2002-08-02, 1:00 am

You won't get better detail than that, he should have used the subject "Everything you wanted to know about DHCP relay agents"

Superb.

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