How DHCP works?

Guys, I have basic doubt, how does DHCP works?

hi,
How DHCP Works?
Before learning the process through which DHCP achieves it’s goal, we first have to understand the different messages that are used in the process.
1. DHCPDISCOVER
It is a DHCP message that marks the beginning of a DHCP interaction between client and server. This message is sent by a client (host or device connected to a network) that is connected to a local subnet. It’s a broadcast message that uses 255.255.255.255 as destination IP address while the source IP address is 0.0.0.0
2. DHCPOFFER
It is DHCP message that is sent in response to DHCPDISCOVER by a DHCP server to DHCP client. This message contains the network configuration settings for the client that sent the DHCPDISCOVER message.
3. DHCPREQUEST
This DHCP message is sent in response to DHCPOFFER indicating that the client has accepted the network configuration sent in DHCPOFFER message from the server.
4. DHCPACK
This message is sent by the DHCP server in response to DHCPREQUEST recieved from the client. This message marks the end of the process that started with DHCPDISCOVER. The DHCPACK message is nothing but an acknowledgement by the DHCP server that authorizes the DHCP client to start using the network configuration it received from the DHCP server earlier.
5. DHCPNAK
This message is the exact opposite to DHCPACK described above. This message is sent by the DHCP server when it is not able to satisfy the DHCPREQUEST message from the client.
6. DHCPDECLINE
This message is sent from the DHCP client to the server in case the client finds that the IP address assigned by DHCP server is already in use.
7. DHCPINFORM
This message is sent from the DHCP client in case the IP address is statically configured on the client and only other network settings or configurations are desired to be dynamically acquired from DHCP server.
8. DHCPRELEASE
This message is sent by the DHCP client in case it wants to terminate the lease of network address it has be provided by DHCP server.

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How DHCP scope will work between two Wireless contoller

Dear All,
I would like to inform you that we are going to deploy Wireless Network with redundancy of Wireless LAN Controller and we need to figure out how DHCP scope would work during fail over any one of Wireless LAN controller and DHCP Server .I have two site where Two Differenet DHCP Server would be palced with different DHCP socpe.So My query is that if Site-A(according to attached diagram) DHCP Server and controller fails how Wireless client will take the DHCP scope from Site-B(according to attached diagram) DHCP Server as it has been configured different DHCP Scope.Can any one tell me whether i can configure same DHCP Scope at Both Site's DHCP Server.
Is there any way to configure same DHCP Scope for two sites.For your infromation client wants two Different DHCP Server with different scope for Two Site and how redundancy would be ensured if any one WLC or DHCP goes down.
I am eagerly waiting for your reply as early as possible.Please help to figure out the solution.
I am going to attached Sample Design for your reference.
Thanks and regards
Erfan

Erfan:
My query was that if one wireless client already associated
WLC-A with one IP block of Location-A (DHCP Server) using SSID named TEST. If DHCP-A or WLC-A goes down then how that same client would associate with WLC-B and get the IP Block from Location-B (DHCP Server) using same SSID name TEST.
In this case the clinets connected to the APs in location A will disconnect (if the WLC went down) and they have to connect again when the APs join WLC-B. They will get IP address from location B block then.
If DHCP went down when new clinets try to connect the primary DHCP is down so they are referred to the secondary DHCP. connected clinets will disconnect only when their DHCP lease times out. They will try to renew but the DHCP server is not available. They will disconnect then and connect again and getting IP from B site.
1. How we will create same policy for that two different block using same SSID.
what policy? where?..etc?
2. client would be connected with Access point but they will get the IP through VLAN interface of the Controller and we have to assign IP helper address in the interface vlan.So how the the client would get the IP block if we assign two IP helper address in the interface vlan in case of failure of DHCP and WLC of one location.
3. If we assign two IP helper address then which DHCP Server will release the IP for client and we can make delay between two DHCP Server to release the IP address.
If two IP helpers are configured the switch will send them both the client's request and they client receives two offers. The clients chooses one of the offers. Usually the clinet will accept the faster DHCP server to respond.
If you are using the DHCP on the WLC then it is different. The WLC will always try to reach the primary DHCP server as long as it is reachable. If the primary DHCP is not reachable then it falls back to the secondary DHCP server.
Note that when you use IP helper then you usually disable DHCP Proxy feature on the controller. Do you have it disabled?

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Question on how networking works with new Macbook Pro

Hi,
I have a question about how networking works with my new Macbook Pro. This is my first laptop so am new to mobile computing. I am about to configure it to replace my desktop which uses a wired DSL connection. Once I have my Macbook Pro configured to run off the DSL modem, what happens when I take this computer to a location that has ethernet? Will just plugging in the ethernet cable be enough to get on line? Or is there further configuration work that needs to be done?
I used a Windows laptop from work and all I had to do was plug it in to a hotel ethernet cable to get on line. However, this laptop was never configured to run on my DSL network so I am not certain if that makes things more complicated.
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Hi
Your MacBook Pro should just work when plugged into an ethernet connection.
Just check something, Open Network Preferences, you can select it from the Airport icon in the menu bar.
In the left-hand pane click on Ethernet and just check that it is set to configure using DHCP in the right-hand pane, that's it.
So when you plug in the ethernet cable it will ask the router for an IP address and off you go.
I assume that any system you plug into will use DHCP rather than static IP addresses. If it is a static IP address, you will need to manually configure the ethernet settings by inputting the IP address and subnet mask info plus DNS servers.
Usually it is done with DHCP and you don't have to do a thing and likewise your home DSL is DHCP?
If not then you will have to change your settings, make a 'Hotel' setting which you can use when in hotels and keep your 'Home' set-up for when you are at home. In the pull down menu select Edit Locations to add new ones.
Phil
Message was edited by: Philip Tyler

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Phil,
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AC

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Couldn't thank you more

Hi,
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How DHCP works?

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