IP routing 15

A subnet address is created by increasing the network portion to include a subnet address, thus decreasing the host portion of the IP address. For example, in the address 128.32.10.0, the network portion is 128.32, while the subnet is found in the first octet of the host portion (10). A subnet mask is applied to the IP address and identifies the network and host portions of the address.

"Subnet masks for Class B and Class C IP addresses" (page 15)illustrates how subnet masks used with Class B and Class C addresses can create differing numbers of subnets and hosts. This example shows the use of the zero subnet, which is permitted on a Nortel Ethernet Routing Switch 5510.

Subnet masks for Class B and Class C IP addresses

Number

Subnet Mask

Number of Subnets

Number of Hosts

of bits

(Recommended)

per Subnet

 

 

 

 

 

 

 

Class B

 

 

 

 

 

2

255.255.192.0

2

16 382

 

 

 

 

3

255.255.224.0

6

8 190

 

 

 

 

4

255.255.240.0

14

4 094

 

 

 

 

5

255.255.248.0

30

2 046

 

 

 

 

6

255.255.252.0

62

1 022

 

 

 

 

7

255.255.254.0

126

510

 

 

 

 

8

255.255.255.0

254

254

 

 

 

 

9

255.255.255.128

510

126

 

 

 

 

10

255.255.255.192

1 022

62

 

 

 

 

11

255.255.255.224

2 046

30

 

 

 

 

12

255.255.255.240

4 094

14

 

 

 

 

13

255.255.255.248

8 190

6

 

 

 

 

14

255.255.255.252

16 382

2

 

 

 

 

 

 

Class C

 

 

 

 

 

1

255.255.255.128

0

126

 

 

 

 

2

255.255.255.192

2

62

 

 

 

 

3

255.255.255.224

6

30

 

 

 

 

4

255.255.255.240

14

14

 

 

 

 

5

255.255.255.248

30

6

 

 

 

 

6

255.255.255.252

62

2

 

 

 

 

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

Copyright © 2005-2007, Nortel Networks

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Image 15
Nortel Networks NN47200-503 manual IP routing