| Author |
Q. about RFC1542 compliant router
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| creamy_stew 2001-10-01, 8:31 am |
| Hi folks!
If a DHCP server is to serve two or more subnets by means of an RFC1542 compliant router/DHCP relay, how does it know which clients belong to which subnet?
Am I missing something basic here?
/creamy | |
| chodan 2001-10-06, 12:40 pm |
| I don`t belive a dhcp server will supply an address to its own subnet that is outside the range indicated by the subnet mask on its own network interface.
Also if the request comes from another subnet and the server has a scope set up for that subnet it will assign a host address that applies for that subnet.
If I am incorrect in this someone please correct me.
Chodan | |
| el duderino 2001-10-06, 1:40 pm |
| The DHCP server will get the subnet address from the relay agent (the relay agent's IP address, which will be from the same subnet as the requesting client so tha is how the DHCP server knows what subnet the request came from) and, if the DHCP server has a scope set up for that subnet, it will provide an IP address from the correct scope to the client computer on the 'remote' subnet. I hope I didn't confuse this too much.  | |
| Joe Blacke 2001-10-06, 5:10 pm |
| quote:
Originally posted by chodan
[B]I don`t belive a dhcp server will supply an address to its own subnet that is outside the range indicated by the subnet mask on its own network interface.
Correct, unless you combine scopes by supernetting and create superscopes. | |
| chodan 2001-10-06, 8:09 pm |
| Cool
and you wouldn`t have to apply a supernetted mask to the interface also? | |
| Joe Blacke 2001-10-06, 9:56 pm |
| I'm not sure I understand what your trying to say?
The DHCP server would have a network address, and subnet mask that is set manually. It would be a valid address within the ranges for the subnet.
For example: a DHCP server with a 10.1.x.x address can assign a 10.2.x.x, OR a 10.1.x.x address to a client on the same subnet. Multiple scopes have to be configured on the DHCP server, and then combined into one superscope. The only problem, is that you can't determine which subnet address will be given to the client without using reservations. The client could get a 10.1 once and a 10.2 the next 100 times, but then go back to 10.1. | |
| chodan 2001-10-07, 9:13 am |
| I`m not sure why you would combine 2 seperate scopes into one superscope in that case.
Wouldn`t you just create a scope for each subnet and leave it at that?
I need to dig up some more info on DHCP hehe
I searched technet for info on "DHCP in a routed environment".
All the articles I found assumed you were putting a DHCP server on every subnet.
Not very helpful in this case.
PS: I also searched for "DHCP relay agent"
and recieved 0 hits.
Oh well | |
| Joe Blacke 2001-10-07, 9:30 am |
| You create superscopes because:
You ran out of IP addresses for one subnet, but still have more clients that need addresses. You combine the scopes and every client on the subnet can use an IP address that is part of the superscope.
You will not see superscopes when using Reserved IP addresses, for the most part. It can be usesfull when you can't afford to waste public addresses.
Don't confuse subnets with scopes. We are only talking about ONE subnet, but two scopes of IP addresses apply. | |
| chodan 2001-10-07, 9:39 am |
| Gotcha
That was exactly what I was doing. | |
| creamy_stew 2001-10-08, 2:37 am |
| Ok, just to make sure I got this:
Scenario:
DHCP relay on network 11.0.0.0 pointing to the DHCP server
DHCP server on network 10.0.0.0
DHCP server has a superscope consisting of
-scopeA 10.0.0.1-10.255.255.254
-scopeB 11.0.0.1-11.255.255.254
Both scopes are active
The DHCP server will now automatically (without further config.)assign addresses in the range 11.0.0.1-11.255.255.254 to clients on the 11.0.0.0 network
Is this all there is to it?
/creamy | |
| rnewt6926 2001-10-18, 5:56 pm |
| Look up GIADDR in your 2K Server help and it will explain how a single DHCP server handles multiple scopes on multiple subnets.
Hope that helps | |
| creamy_stew 2001-10-30, 8:38 am |
| Thanks all for replying, esp rnewt6926!
/creamy | |
| m22baker 2001-11-09, 6:40 pm |
| This is the way it works:
If you have a DHCP Server connected to a router with three subnets(the DHCP server on one of them), the computer without the IP address tells the DHCP Relay Agent(on it's own subnet) that it needs an IP address. The Relay Agent contacts the DHCP Server and tells it it needs an IP address because somebody needs it. The DHCP server sends the IP address to the relay agent and the relay agent sends the IP address to the requesting computer.
If you meant an rfc 2131 compliant router, then it would be a different issue(RFC 2131 uses an IP Helper to send packets to the proper place). |
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