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IP Addressing

IP SubnettingStatic SubnetVariable Length Subnet Masks(VLSMs)

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The Hierarchical IP AddressingScheme

IP address consists of 32 bits of information.

You can depict an IP address using one of threemethods:

Dotted-decimal, as in 172.16.30.56 Binary, as in 10101100.00010000.00011110.00111000

Hexadecimal, as in AC .10.1 E .38

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Network Addressing

Network Address Range: Class A00000000 = 001111111 = 127

Network Address Range: Class B10 000000 = 12810 111111 = 191

Network Address Range: Class C 110 00000 = 192 110 11111 = 223

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Network Address Ranges: Classes D and E

The addresses between 224 and 255 arereserved for Class D and E networks. Class

D (224 239) is used for multicastaddresses and Class E (240 255) for scientific purposes,

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Summary of the three classes of networks

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Class A Addresses

network.node.node.node For example, in the IP address 49.22.102.70 , the 49 is thenetwork address, and 22.102.70 is the node address.

the network address of all 0s (0000 0000) is reserved todesignate the default route

Additionally, the address 127 , which is reserved for diagnostics, cant be used either,

you can really only use the numbers 1 to 126 to designateClass A network addresses. This

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Class C Addresses

network.network.network.node example IP address 192.168.100.102, thenetwork address is 192.168.100, and the nodeaddress is 102.

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Private IP Addresses

These addresses can be used on a private network,but theyre not routable through the Internet.

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2004 Cisco Systems, Inc. All rights reserved. ICND v2.2 3-21

IP Subnetting

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CIDR -- Classless InterDomainRouting 192.60.128.0 (11000000.00111100.10000000.00000000 ) Class C subnet address192.60.129.0 (11000000.00111100.10000001.00000000 ) Class C subnet address192.60.130.0 (11000000.00111100.10000010.00000000 ) Class C subnet address192.60.131.0 (11000000.00111100.10000011.00000000 ) Class C subnet address--------------------------------------------------------

192.60.128.0 (11000000.00111100.10000000.00000000 ) Supernetted Subnet address255.255.252.0 (11111111.11111111.11111100.00000000 ) Subnet Mask192.60.131.255 (11000000.00111100.10000011.11111111 ) Broadcast address

In this example, the subnet 192.60.128.0 includes all the addresses from192.60.128.0 to 192.60.131.255 . As you can see in the binaryrepresentation of the subnet mask, the Network portion of the addressis 22 bits long, and the host portion is 10 bits long .

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CIDR(1)

Under CIDR, the subnet mask notation is reduced toa simplified shorthand . Instead of spelling out the bitsof the subnet mask, it is simply listed as the number of 1s bits that start the mask . In the above example,

instead of writing the address and subnet mask as192.60.128.0, Subnet Mask 255.255.252.0 the network address would be written simply as:192.60.128.0/22

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CIDR(2)

The use of a CIDR notated address is thesame as for a Classful address . Classfuladdresses can easily be written in CIDRnotation (Class A = /8, Class B = /16, and ClassC = /24 )

Reference http ://www .sluug .org /resources /cidr .html
http://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.htmlhttp://www.sluug.org/resources/cidr.html

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What Is a Variable-LengthSubnet Mask?

Subnet 172.16.14.0/24 is divided into smaller subnetsSubnet with one mask (/27)Then further subnet one of the unused /27 subnets into

multiple /30 subnets

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Calculating VLSMs

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A Working VLSM Example

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What Is Route Summarization?

Routing protocols can summarize addresses of severalnetworks into one address.

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Summarizing Within an Octet

S i i Add i

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Summarizing Addresses in aVLSM-Designed Network

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Implementation Considerations

Multiple IP addresses must have the samehighest-order bits.

Routing decisions are made based on theentire address.

Routing protocols must carry the prefix(subnet mask) length.

R S i i

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Route SummarizationOperation in Cisco Routers

Supports host-specific routes, blocks of networks,and default routesRouters use longest match

192.16.5.33 /32 Host192.16.5.32 /27 Subnet192.16.5.0 /24 Network192.16.0.0 /16 Block of Networks0.0.0.0 /0 Default

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Summarizing Routes in a Discontiguous Network

RIPv1 and IGRP do not advertise subnets, and thereforecannot support discontiguous subnets.OSPF, EIGRP, and RIPv2 can advertise subnets, andtherefore can support discontiguous subnets.

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Chapter 4 IP VLSMs(3-2548)

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