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As you people know that you can easily identify systems in your network that are running SQL SERVER INSTANCE but is this possible that I can force DHCP to recognize my application?

example: I have many clients and a single server. but in secure networks out-bond traffic and port listeners are blocked. so I am trying to use reverse model.

I am successful in getting information about all the leased IP through querying DHCP but I want that my clients can query DHCP that where is my server and I want this without having access to DHCP server.

Scenario#1: Server Running on: DHCP: when my client application runs on some machine it query DHCP about the server and DHCP should tell him that your server is running @


  1. Server Started, Begins initialization

  2. Requested IP from DHCP Server [broadcast a packet called DHCP Discover packet] Server replies and assigns an IP

  3. DHCP Offer Paket [Determines Configuration]
  4. DHCP REQUEST ... and continues finally get an IP

What I want is to send some Vendor Specific information to DHCP server so that it can store it its filed 43. and When my filed 43 aware [parsing logic present in client]client will turn on it will send a packet by filling field 60 so that DHCP server returns that vendor specific information to my client i.e vendor specific information stored in field 43. I can store N bytes there means I can store my Server IP address and that can be useful for clients.

I hope this is clear now.. if you are interested then kindly read


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I thought SQL instances were identified via SQL Browser Service, not DHCP. – jscott Oct 22 '10 at 13:53
I think he wants his application to stick the location of the SQL server into the DHCP server when it finds it, so network clients can query for it from DHCP, which isn't what it's designed to do and I don't think he can stick random arbitrary data into the DHCP server without administrative privs. He'd be better off periodically sending the location over UDP or sticking it as a static configuration on the network. – Bart Silverstrim Oct 22 '10 at 14:10
DHCP only assigns IPs (and certain options) to computers and keeps track of what computer (by MAC address) it has assigned an IP to. DHCP has nothing to do with SQL whatsoever. SQL users a location service (which has nothing to do with DHCP) as jscott pointed out. What you are asking for doesn't exist. – Chris S Oct 22 '10 at 14:49
DHCP does have extensions that allow for vendor-specific information to be included; it's conceivable that you could (A) rewrite your dhcp server to provide information about your SQL servers, and (B) rewrite your DHCP clients so they could understand this information and do something useful with it. Possible. Not sensible, but possible. – James Polley Oct 25 '10 at 22:50
This questions demonstrates a poor understanding of both DHCP and DNS. The latter being the correct way to do this. – John Gardeniers Oct 26 '10 at 1:29

Yep, this is easy, it's called DNS - basically each time any machine whether it's a client or server, is given an IP address by a DHCP server the DHCP server registers a DNS entry for that device. All of the devices look to the same DNS server/s and can therefore request any registered device's IP address as required. This is a robust system used pretty much everywhere. Obviously you've not mentioned you operating systems but this is available for any you have.

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Sorry dear I request you to kindly read the question again. Thanks for your kind consideration. – AZ_ Oct 22 '10 at 12:48
Sorry, you're still not clear, do you want the client to know the name of the DHCP server that gave it its IP address or do you want to know how to find a server? you're really far from clear. – Chopper3 Oct 22 '10 at 12:52
I want to store a vendor specific information (that could be any thing) in DHCP server. So that my client can query DHCP server go get data from "vendor specific information" that is filed 43 to get my server ip address. – AZ_ Oct 22 '10 at 13:23
Otherwise if I have 200 pc computers (where broadcastPING, SLP, port listeners are blocked) will be very difficult to search my client. – AZ_ Oct 22 '10 at 13:24
But that's not what it's there for, you seem very confused about this - you just use DHCP to get IP addresses, register DNS addresses and if needed store other info in the scope DB. Nobody uses this DB from the client side to make destination choices - it makes no sense, that's what DNS is for. That extra information is usually things, if used, like OS version, make/model etc. It just lets the DHCP server know who's asked for an address, as it would normally only have a MAC to go on. – Chopper3 Oct 22 '10 at 13:42

I don't think you can do this via DHCP without making changes on the DHCP server. The DHCP protocol has option 43 - Vendor Specific Information which would allow you to encode your server's address.

share|improve this answer
Option 43 has unspecified amount of bytes available to store something and client can ask DHCP server to give that specific information but HOW ?? :) – AZ_ Oct 22 '10 at 12:33
I have found something interesting but still did not find a way to accomplish it pragmatically… – AZ_ Oct 22 '10 at 12:47
Wonderful... – AZ_ Oct 22 '10 at 13:07
@Chopper3 is correct - the better way to do this is to configure the DNS to point to the server that supports your application then have your hosts do a simple DNS lookup to get the info they need. If you really want to do it with DHCP programatically then you should ask over on stackoverflow – Iain Oct 22 '10 at 13:07
Vendor Specific DHCP (option 43) in Windows CE – AZ_ Oct 25 '10 at 9:58

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