Subnetting with class a and class b networks – ZyXEL Communications Internet Security Gateway 10~100 Series User Manual
Page 53
ZyWALL 10~100 Series Internet Security Gateway
IP Subnetting
8-7
Chart 8-12 Class C Subnet Planning
NO. “BORROWED” HOST BITS
SUBNET MASK
NO. SUBNETS NO. HOSTS PER SUBNET
1 255.255.255.128
(/25)
2
126
2 255.255.255.192
(/26)
4
62
3 255.255.255.224
(/27)
8
30
4 255.255.255.240
(/28)
16
14
5 255.255.255.248
(/29)
32
6
6 255.255.255.252
(/30)
64
2
7 255.255.255.254
(/31)
128
1
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 Chart 8-1) available for subnetting.
The following table is a summary for class “B” subnet planning.
Chart 8-13 Class B Subnet Planning
NO. “BORROWED” HOST BITS
SUBNET MASK
NO. SUBNETS
NO. HOSTS PER SUBNET
1 255.255.128.0
(/17)
2 32766
2 255.255.192.0
(/18)
4 16382
3 255.255.224.0
(/19)
8
8190
4 255.255.240.0
(/20)
16 4094
5 255.255.248.0
(/21)
32 2046
6 255.255.252.0
(/22)
64 1022
7 255.255.254.0
(/23)
128 510
8 255.255.255.0
(/24)
256 254