VLSM and CIDR : VLSM and CIDR Routing Protocols and Concepts – Chapter 6
Objectives : Objectives Compare and contrast classful and classless IP addressing.
Review VLSM and explain the benefits of classless IP addressing.
Describe the role of the Classless Inter-Domain Routing (CIDR) standard in making efficient use of scarce IPv4 addresses
Practice implementing VLSM and CIDR
Key Terms : Key Terms Classful IP Addressing
Discontiguous Address Assignment
Supernet/Supernetting
VLSM
CIDR
Introduction : Introduction Prior to 1981, IP addresses used only the first 8 bits to specify the network portion of the address
In 1981, RFC 791 modified the IPv4 32-bit address to allow for three different classes
IP address space was depleting rapidly
the Internet Engineering Task Force (IETF) introduced Classless Inter-Domain Routing (CIDR)
CIDR uses Variable Length Subnet Masking (VLSM) to help conserve address space.
-VLSM is simply subnetting a subnet
Classful and Classless IP Addressing : Classful and Classless IP Addressing Classful IP addressing
As of January 2007, there are over 433 million hosts on internet
Initiatives to conserve IPv4 address space include:
-VLSM & CIDR notation (1993, RFC 1519)
-Network Address Translation (1994, RFC 1631)
-Private Addressing (1996, RFC 1918)
Classful and Classless IP Addressing : Classful and Classless IP Addressing The High Order Bits
These are the leftmost bits in a 32 bit address
IP Classes - Review : IP Classes - Review Classes of IP addresses are identified by the decimal number of the 1st octet
Class A address begin with a 0 bit
Range of class A addresses = 0.0.0.0 to 127.255.255.255
Class B address begin with a 1 bit and a 0 bit
Range of class B addresses = 128.0.0.0 to 191.255.255.255
Class C addresses begin with two 1 bits & a 0 bit
Range of class C addresses = 192.0.0.0 to 223.255.255.255.
Network vs. Host Based on Subnet Mask : Network vs. Host Based on Subnet Mask
Classful Routing Protocols : Classful Routing Protocols Classful Routing Updates
Recall that classful routing protocols (i.e. RIPv1) do not send subnet masks in their routing updates
Classful routing protocols assume the classful mask
Classless Inter-domain Routing (CIDR) : Classless Inter-domain Routing (CIDR) Advantage of CIDR (RFC 1517) :
-More efficient use of IPv4 address space
-Route summarization
VIDEO - http://www.youtube.com/watch?v=jh5-V27DpCQ
CIDR & Route Summarization : CIDR & Route Summarization CIDR allows for routes to be summarized as a single route
Variable Length Subnet Masking (VLSM)
Allows a subnet to be further sub-netted according to individual needs
Prefix Aggregation a.k.a. Route Summarization
Classless Routing Protocols : Classless Routing Protocols Characteristics of classless routing protocols:
Routing updates include the subnet mask
Supports VLSM
Supports Route Summarization
Classful and Classless IP Addressing : Classful and Classless IP Addressing Classless Routing Protocol
VLSM : VLSM VLSM – the process of sub-netting a subnet to fit your needs
-Example:
Subnet 10.1.0.0/16, 8 more bits are borrowed again, to create 256 subnets with a /24 mask.
-Mask allows for 254 host addresses per subnet
-Subnets range from: 10.1.0.0 / 24 to 10.1.255.0 / 24
Route Summarization in CIDR : Route Summarization in CIDR Routes are summarized with masks that are less than that of the default classful mask
-Example:
172.16.0.0 / 13 is the summarized route for the 172.16.0.0 / 16 to 172.23.0.0 / 16 classful networks
Steps to Calculate a Summary Route : Steps to Calculate a Summary Route List networks in binary format
Count number of left most matching bits to determine summary route’s mask
Copy the matching bits and add zero bits to determine the summarized network address
Chapter 6 Labs : Chapter 6 Labs 6.4.1: Basic VLSM Calculation and Addressing Design
6.4.4: Basic Route Summarization (using Packet Tracer)
Slide 18 :