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Subnets.md

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66 lines (54 loc) · 3.26 KB
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2024-12-11T20:01
2025-01-05 14:55
network
ip
ip-address
subnet
ipv4
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An IP network is a pool of devices connected by a network, where each device is identified in the network using it's IP address. e.g. the internet is an IP network. Internet Protocol (IP) is a set of rules and procedures that govern how devices identify themselves and exchange data with other devices on a network.

An IP network can be partitioned into smaller (non-overlapping) subnetworks (i.e. subnets), each subnet with it's own IP address range.

IPv4

An IPv4 address is a 32-bit number, meaning a number which is represented by 32 binary digits. e.g. 10011000011001100101010111001100 is a 32-bit number.

An IP address is divided into four 8-bit numbers (called octets).

For example, the IP address

192.168.1.20

in binary is

11000000.10101000.00000001.00010100

IPv4 Subnets

A subnet mask is a 32-bit number which is used to subdivide the IP network (pool of IP addresses) into a network portion and a host portion.

Example: The netmask 255.255.252.0 in binary is 11111111.11111111.11111100.00000000 Applying this netmask to the IP address 192.168.1.20 (11000000.10101000.00000001.00010100) divides the IP address into a network portion and a host portion:

IP Addr: 1 1 0 0 0 0 0 0 . 1 0 1 0 1 0 0 0 . 0 0 0 0 0 0 0 1 . 0 0 0 1 0 1 0 0
NETMASK: 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 0 0 . 0 0 0 0 0 0 0 0
Network: _ _ _ _ _ _ _ _   _ _ _ _ _ _ _ _   _ _ _ _ _ _  
Host:                                                    _ _   _ _ _ _ _ _ _ _

All devices within the subnet have the same network values, but each connected device has a unique host value. The are 2 reserved IP addresses in the subnet - the network and broadcast IP addresses.

Network: 11000000.10101000.00000000.00000000 (192.168.0.0) Broadcast: 11000000.10101000.00000011.11111111 (192.168.3.255) Host range (min): 11000000.10101000.00000000.00000001 (192.168.0.1) Host range (max): 11000000.10101000.00000011.11111110 (192.168.3.254)

In CIDR notation, the subnet of the IP address 192.168.1.20 would usually be notated 192.168.0.0/22 (i.e. just showing the network portion of the IP address). The /22 is the number of bits in the network portion.

Therefore, the number of available IP addresses in a /22 subnet is $(2^{32-22})=1024$ (noting that 2 of them cannot be assigned to individual hosts, but are reserved for "network" and "broadcast" addresses, so 1022 are actually assignable). In general (aside from the exception /31), number of IP addresses available in a $/n$ subnet is $2^{32-n}$

There is something called a "wildcard", which is just the inverse of the subnet mask.

References

Related

  • Links to other notes which are directly related go here