ZyXEL Communications Internet Security Gateway ZyWALL 2 Series User Manual page 567

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5
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Subnetting With Class A and Class B Networks.
For class "A" and class "B" addresses the subnet mask also determines which bits are part of the network
number and which are part of the host ID.
A class "B" address has two host ID octets available for subnetting and a class "A" address has three host ID
octets (see Error! Reference source not found.) available for subnetting.
The following table is a summary for class "B" subnet planning.
NO. "BORROWED" HOST BITS
1
2
3
4
5
6
7
8
9
10
11
12
13
IP Subnetting
255.255.255.240 (/28)
255.255.255.248 (/29)
255.255.255.252 (/30)
255.255.255.254 (/31)
Chart I-13 Class B Subnet Planning
SUBNET MASK
255.255.128.0 (/17)
255.255.192.0 (/18)
255.255.224.0 (/19)
255.255.240.0 (/20)
255.255.248.0 (/21)
255.255.252.0 (/22)
255.255.254.0 (/23)
255.255.255.0 (/24)
255.255.255.128
(/25)
255.255.255.192
(/26)
255.255.255.224
(/27)
255.255.255.240
(/28)
255.255.255.248
(/29)
ZyWALL 2 Series User's Guide
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NO. SUBNETS NO. HOSTS PER SUBNET
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
14
6
2
1
32766
16382
8190
4094
2046
1022
510
254
126
62
30
14
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