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IPv6 Training (Cisco): What is DHCP for IPv6 Rapid Commit? Hot

Added: 08/15/2008, Hits: 7,744, Rating: 0, Comments: 0, Votes: 0
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Rapid-Commit; is the process (option) in which a Requesting Router (DHCP Client) obtains “configurable information” (configurable parameters) from a Delegating Router (DHCP Server) by using a rapid DHCPv6 two-message exchange. The messages that are exchanged between the two routers (RR and DR) are called the DHCPv6 “SOLICIT” message and the DHCPv6 “REPLY” message.

I know you maybe saying, well so what.

But, you must remember when a DHCP Client (The RR) normally needs to obtain “configurable information” from a DHCP Server (The DR) it will use the default DHCPv6 four-message exchange. That means the following four DHCPv6 messages are going to be sent between the RR and DR.

  • The DHCPv6 “SOLICIT” message

  • The DHCPv6 “ADVERTISE message

  • The DHCPv6 “REQUEST” message

  • The DHCPv6 “REPLY” message

The DHCPv6 “SOLICIT” message is sent out by the DHCP Client (The RR) to verify that there is a DHCP Server (a DR) available to handle its requests (demands).

The DHCPv6 “ADVERTISE message is sent out by the DHCP Server (The DR) as a reply to the DHCPv6 “SOLICIT” message that was sent out by the DHCP Client (The RR); basically, this message is sent by the DR to tell the RR that it is the DHCP Server that can handle the requests (demands).

The DHCPv6 “REQUEST” message is sent out by the DHCP Client (The RR) to request (demand) its “configurable information” from the DHCP Server (a DR). In other words, the DHCP Client (The RR) sends this type of message to a DHCP Server (a DR) when it is saying “Hey, DHCP Server (DR) give me my configurable information, Right Now!”

The DHCPv6 “REPLY” message is sent out by the DHCP Server (The DR) to the DHCP Client (The RR), and it contains the “configurable information” that the DHCP Client (The RR) requested (demanded). In other words, the DHCP Server (The DR) is sending this message to the DHCP Client (The RR) to say “O.K. here is your configurable information that you requested (demanded), Good Luck.”
Well, by now you should begin to understand why the “rapid-commit” option (mechanism) is such a wonderful option (mechanism), because it is actually a short cut to allow a RR (DHCP client) receive “configurable information” from a DR (DHCP server).

Because, the RR (DHCP client) that is requesting the “configurable information” from the DR (the DHCP Server) is going to include the "rapid-commit" option in the SOLICIT message that it sends; so it can inform the DR (DHCP server) to send a REPLY message immediately.

By the way, just in case if you were wondering; the “rapid-commit” option has to configured on a RR’s (DHCP client’s) interface as well as a DR’s (DHCP server’s) interface to work properly.

In this entire article, I used the term “configurable information” so you could quickly learn how the “rapid-commit” option is used.

But, from a Cisco Systems standpoint the “rapid-commit” option (mechanism) is used by a RR (DHCP client) to request IPv6 Prefix information (Prefix Delegation) from a DR (DHCP server). In other words, Cisco Systems uses the “rapid-commit” option so a RR can request (retrieve) IPv6 Prefixes (address blocks) from a DR.

I invite you to visit my website at where you’ll find the latest information regarding Cisco IPv6 Design and Implementation Techniques. And, also learn more about the new "Cisco IPv6 Video Accelerated Training Course" which contains over 3000 videos that will teach you all you need to know about Desiging, Building, and Deploying Cisco IPv6 networks. (Guaranteed)

To your success,

Charles Ross
CCNP #CSCO10444244

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