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21
Administration for Network Connectivity
555-233-504 — Issue 1 — April 2000 CID: 77730
1 Networking Overview
Valid subnet masks The valid subnets for each Class of address are:
Notice that all 5 valid Class C subnet masks can also be valid Class B or Class A
subnet masks, and all 13 valid Class B subnet masks can also be valid Class A subnet
masks.
For example,
255.255.255.224
is a valid subnet mask for all three address
classes. It allows 6 (2
3
−
2) subnetworks for Class C addresses, 2046 (2
11
−
2)
subnetworks for Class B addresses and 524,286 (2
19
−
2)subnetworks for Class A
addresses. Each of these subnetworks can have 30 (2
5
−
2) hosts.
Class A
(default 255.0.0.0)
Class B:
(default 255.255.0.0)
Class C
(default 255.255.255.0)
255.192.0.0 255.255.192.0 255.255.255.192
255.224.0.0 255.255.224.0 255.255.255.224
255.240.0.0 255.255.240.0 255.255.255.240
255.248.0.0 255.255.248.0 255.255.255.248
255.252.0.0 255.255.252.0 255.255.255.252
255.254.0.0 255.255.254.0
255.255.0.0 255.255.255.0
255.255.128.0 255.255.255.128
255.255.192.0 255.255.255.192
255.255.224.0 255.255.255.224
255.255.240.0 255.255.255.240
255.255.248.0 255.255.255.248
255.255.252.0 255.255.255.252
255.255.254.0
255.255.255.0
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252