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DHCP - Info

Latest reply: Aug 16, 2018 22:19:01 1241 5 1 0 0
DHCP is anApplication Protocol.
 
  • The main purpose
Automatethe process of providing, maintenance and control the addressing of anenterprise network especially for end devices.
  • Why?
Becausemaking this process manual is tedious and lead to many issues as addressduplication.
 
  • Who can be a DHCP server?
    • Router  
    • Core Switch  
    • Firewall  
    • Server

 
  • Which kind of problems solves     DHCP?
    • Duplicate IP Address  
    • Human Error  
    • Complex administration

 
  • DHCP supports three     mechanisms for IP address allocation:
  • Automatic      allocation assigning a permanent IP Address to a host.  
  • Dynamic allocation assigned      an IP address for a limited period of time.  
  • Manual Allocation where an      administrator manually define which IP address assigned to the host.
 
  • Manual allocations allows     DHCP to be used to eliminate the error-prone process.
 
DHCP Messages


  DHCP Discover
  
  Broadcast/ UDP  messaged used to located a DHCP server.
  
  DHCP Offer
  
  Unicast  Server responds  with an offer of configuration.
  
  DHCP request
  
  Broadcast
Client responds for:
    1)To confirm that accepts one offer from one DHCP server declining  others.
    2)When was restarted and send a message request to confirm if he can use  the last leased configurations. When the client was logging into the network  before.

  3)Extending the  lease on a particular address.
   
  
  DHCP ACK
  
  Unicast Sent by DHCP Server to acknowledge the  Request message.
  
  DHCP NACK
  
  Server  declined  the client's Request Message.
  
  DHCP RELEASE
  
  Client cancels the  remaining lease
  
  DHCP Inform  Message
  
  After a host has  IP address and Mask sent this message to obtain gateway address and DNS  addresses.
  
  DHCP DECLINE
  
  Sent by a client  do inform the server the IP address is under use.
  
 
 
Afterreceiving a DHCP Discover message each DHCP Server selects an unassigned IPAddress from the pool and sends a DHCP Offers message with the assigned IPAddress and others configurations. Ifmultiples DHCP servers offers the client accepts the first DHCP offers Messagereceived.


Three timers are set on the     DHCP client.
 
  Release Renewal
  
  At what time needs  to renew the lease IP address.  Default 50% of the lease time.
  
  Rebinding timer
  
  The time which  will wait to have an answer from the DHCP server. Default 12.5% of the lease time.
  
  Lease  timer
  
  Final timer in the  expiration process. If the client doesn't receive an answer before the lease  time expires the DHCP client must stop using the current IP Address  immediately. And start a new DHCP DISCOVER.
  

  • The leased     time by default is 1 day.
 
  Port
  
  Server
  
  Protocol
  
  67,68
  
  DHCP
  
  UDP
  
 


DHCP - Info-2727197-1
This post was last edited by DiegoXD at 2018-08-16 13:44.
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Fernandoizsa
Created Aug 16, 2018 13:50:48

key information, its necessary understand how DHCP works also its very important know the negotiation between the DHCP Server & DHCP Client for troubleshootings:)
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j84088811
Created Aug 16, 2018 14:35:58

Very important remember this information and also understanding DHCP working way. When we face an issue about DHCP we can save many time during troubleshooting. :)
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KarimUC
Created Aug 16, 2018 14:38:11

good info
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xelamaster69
Created Aug 16, 2018 14:58:04

Thanks for the information also we need to remember these basic concepts, most of the time we do not remember it. DHCP - Info-2727309-1
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Argentym
Created Aug 16, 2018 22:19:01

Do you know what option delivers metric for GW?
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