Cisco IPv6 Training IPv6 Router Prefix Delegation

What is Prefix Delegation?

By Charles Ross CCNP #CSCO10444244

Well, to quickly answer your question; Prefix Delegation (PD) is considered to be a procedure (mechanism) that is used to automate the delegation of IPv6 prefixes (address blocks). Prefix Delegation is explained in RFC 3769 and is normally used by ISPs, to aid with the process of delegating IPv6 prefixes (address blocks) to their customers.

Cisco’s version of Prefix Delegation (PD) consists of three items a Customer Edge (CE) router, a Provider Edge (PE) router and a AAA server.

The Customer Edge (CE) router which is also known as the Requesting Router (RR) performs like a DHCP client and is located at the customer’s premises; it has the job of requesting IPv6 prefixes (address blocks) from the Provider Edge (PE) router.

The Provider Edge (PE) router which is also known as the Delegating Router (DR) performs like a DHCP server and is located at the ISP’s premises; it has the responsibilities of validating the authenticity and the profile of the Requesting Router (RR) with a AAA server; and also places a route into the ISP’s routing system on the behalf of the Requesting Router (RR) for the delegated prefix.

The reason why the Delegating Router places a route into the ISP’s routing system on the behalf of the Requesting Router (RR) for the delegated prefix; is to avoid the need for a dynamic routing protocol between the Delegating Router (DR) and the Requesting Router (RR). So, in other words, with Cisco’s version of Prefix Delegation the DR and RR are normally directly connected to one another; and only in certain circumstances its appropriate to configure a DHCP Relay router between the DR and RR to allow them to communicate.

Now, just in case if you were wondering; the AAA server that is connected to the DR at the ISP’s location is the server that actually hands out the IPv6 prefixes and passes the IPv6 prefixes to the DR using Radius, so the DR can then pass the IPv6 prefix (address block) information to the RR.

To your success,

Charles Ross

CCNP #CSCO10444244