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Cisco 10000 Series Router Software Configuration Guide
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Chapter 10 Configuring Address Pools
Address Assignment Mechanisms
Benefits of RADIUS-Based Address Assignment
RADIUS is an effective mechanism for providing IP address assignment for remote users:
•
One benefit of RADIUS-based address assignment is its ability to effectively manage the IP address
pools configured on the server. RADIUS can dynamically resize pools as needed, removing
addresses from poorly utilized pools and adding them to pools that run out of addresses.
•
RADIUS supports route summarization and uses profiles configured on the server to provide
efficient addressing and AAA services.
•
RADIUS can also attach a fixed IP address to a remote user’s login.
Limitations of RADIUS-Based Address Assignment
When deciding upon an addressing mechanism, you must weigh the limitations and benefits of
RADIUS-based address assignment. The following are some of the limitations of RADIUS-based
address assignment:
•
Using RADIUS for address assignment can increase the load on the server and slow the server’s
performance.
•
As remote users log on and off, route summarization can become less efficient because it becomes
more difficult for the PE router to have a contiguous set of IP addresses that the PE can summarize
to the RADIUS server.
•
Each time a user logs on or off, the Border Gateway Protocol (BGP) sends update information to the
PE routers to update the VRFs configured on each router.
•
Remote users have limited connectivity during the time it takes for BGP to propagate a newly
configured route to all PE routers.
DHCP-Based Address Assignment
Dynamic Host Configuration Protocol (DHCP) servers allocate IP addresses to remote users, eliminating
the need to configure users individually. DHCP also provides all the parameters that user systems require
to operate and exchange information on the Internet network to which they connect. DHCP is based on
a client/server model. The client software runs on the user system and the server software runs on the
DHCP server.
DHCP uses a lease mechanism that offers an automated, reliable, and safe method for distributing and
reusing addresses in networks, with little need for administrative intervention. As a system
administrator, you can tailor the lease policy to meet the specific needs of your network.
Leases are grouped together in an address pool called a
scope
. The scope defines the set of IP addresses
available for requesting hosts. A lease can be reserved (the host always receives the same IP address) or
dynamic (the host receives the next available, unassigned lease in the scope).
Benefits of DHCP-based Address Assignment
One of the most significant benefits of DHCP is that it can dynamically configure user systems with IP
addresses and associate leases with the assigned addresses. DHCP also provides for multiple servers.
You can configure redundant DHCP servers so that if one server cannot provide leases to requesting
clients, the other one can take over. Existing DHCP clients can continue to keep and renew their leases
without knowing which server is responding to their requests.
