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TOPIC: Some Doubts about DHCP?

Some Doubts about DHCP? 13 years 1 month ago #8189

  • jaiwardhan
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Hi Friends
I was asked this question at an interview. THe person asked if he has 2000 computers in a company. There are 9 DHCP severs to handle the ip address allotment. The company adds more 50 computers in a department . How will the new computers added know out of 9 DHCP servers to which DHCP server they should contact for ip address ?
I got not give the answer of this question. It would be really nice if someone could help me with this question :)
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I could be wrong but..... 13 years 1 month ago #8190

  • Ranger24
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Not a nice question!
For me this question cannot really be answered fully without knowing the architecture of the network.

I would assume that the 2000 machines are over several logical sites which are connected via switches / routers. The switch / router for each logical site would need to be configured as a DHCP relay for it's site.

Simple example:

SWITCH A is configured with a DHCP relay address of is the address of DHCP SERVER 1

SWITCH A recieves a DHCP request from PC "Z"

SWITCH A forwards the DHCP request to The packet has the IP address of SWITCH A as the source address

DHCP SERVER 1 recieves the request and sends a reply to SWITCH A with IP address to be assigned

SWITCH A forwards the reply to PC "Z"

So in answer to the question each of the 50 pcs would use the DHCP server that it's switch/router is configured to use.

I hope this make sense and helps. Maybe someone with a bit more experiance then me can check!


Patience - the last reserve of the any engineer
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DHCP 13 years 1 month ago #8192

  • TheBishop
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Since they didn't give you any detailed information on the design of the network, I would just have given them the simple answer:
When a workstation is added to the network it will send a DHCP broadcast which effectively says "hello, I'm a DHCP client, is there a DHCP server out there that would like to give me an IP address?" One or more DHCP servers may respond to this. The workstation will act on the first response that comes in, which is most likely to be from the nearest (in network terms) DHCP server. So unless they have done something more sophisticated it will most likely be the nearest, most local server to the new clients that will allocate the addresses.
If they wanted more, they would then have to give you more info to get it
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Re: Some Doubts about DHCP? 13 years 1 month ago #8197

  • kcbell
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What is given is there are 2000 PC already in place and with 9 DHCP server. Logically, I would think these 9 DHCP servers are serving 9 VLAN. These 9 VLAN could be 9 separate departments of a company. If the switch is configurated correctly, with the correct VLAN, the PC should be able to get an IP from the correct DHCP server.
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