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TOPIC: DHCP from Server and Router

DHCP from Server and Router 8 years 9 months ago #25216

  • SteveP
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I'm doing CCNA v3.1 and DHCP configuration doesn't come into the syllabus (our tutor said not). Suppose I set up a router and a W2K3 server, each providing a pool of IP addresses and they are connected to a switch. I attach an XP client (configured to obtain the IP address automatically) to the switch, so the question is "which takes precedence in providing the IP address - the router or the W2K3 server?". I guess it doesn't really matter, so long as the client gets an address, but I'm just interested to know how a conflict is resolved.

I don't have access to a server, otherwise I'd set this up and test it for myself.
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Re: DHCP from Server and Router 8 years 9 months ago #25218

  • Smurf
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Its really simple Steve, the one that gets the reply back the quickest, hehe.

Thats basically it........It uses a broadcast mechanism (sent to broadcast address) so both devices will get the request and will respond.

Cheers
Wayne Murphy
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www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
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Re: DHCP from Server and Router 8 years 9 months ago #25226

  • SteveP
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Pah - so simple! I assumed that there must be some clever algorithm or other reason that one would take priority. I was just thinking at a "higher" level.

I realise that a DHCP request involves a broadcast (the "DORA" acronym springs to mind) so, if the server was on the other side of the router (a different LAN to the client), it would be the router which supplied the address becasuse the router wouldn't forward the broadcast from the client.

Thanks for clearing it up for me.
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Re: DHCP from Server and Router 8 years 9 months ago #25243

  • Ozzy_98
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If the DHCP server was on the otehr side of a router, then by default, you wouldn't get DHCP addresses, since routers do not forward broadcasts. Also remember too, there's IP broadcasts (Sent to the last IP address in a range, the 192.168.1.255 for example on the 192.168.1.0 network) and there's physical broadcasts (Sent to the FF:FF:FF:FF mac address)
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Re: DHCP from Server and Router 8 years 8 months ago #25401

If the DHCP server was on the other side of a router, then the router needs to set up as a DHCP Relay agent, so that it can forward the DHCP Request.

Thanks,
Datacom_guy
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Re: DHCP from Server and Router 8 years 8 months ago #25402

  • SteveP
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I'm not familiar with a DHCP Relay agent. I'd better do some googling!
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