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DHCP from Server and Router

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16 years 10 months ago #25216 by SteveP
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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16 years 10 months ago #25218 by Smurf
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
Firewall.cx Team Member
www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
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16 years 9 months ago #25226 by SteveP
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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16 years 9 months ago #25243 by Ozzy_98
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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16 years 9 months ago #25401 by Datacom_guy
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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16 years 9 months ago #25402 by SteveP
I'm not familiar with a DHCP Relay agent. I'd better do some googling!
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