Understanding Subnetting and Its Importance in Networking
Explore the concept of subnetting in networking, where IP networks are divided into smaller subnets. Learn how organizations use subnetting to create efficient network structures and why subnetting is crucial for network management and security within an organization.
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Subnetting ECE 461 Professor Jorg Liebeherr 1
Takeaways Takeaways Subnetting = Dividing an IP network (subnet) into smaller networks Subnetting is done by increasing the network prefix An organization uses subnetting to create smaller networks for its organizational units Subnetting is not visible outside the organization 2
Network Prefix and Interface Identifier Network Prefix and Interface Identifier IP address consists of a network prefix and an interface identifier: 128.100 11.60 netmask 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 0 0 0 0 0 0 255 255 0 0 CIDR notation: Netmask notation: 128.100.11.60/16 128.100.11.60, 255.255.0.0 3
Subnetting Subnetting Scenario: Organization has a large network prefix and wants to create smaller networks UofT Network 128.100.0.0/16 Faculty of Engineering 128.100.11.0/24 Faculty of Arts and Science 128.100.58.0/24 Subnetting: Use a portion of the interface identifier to identify a smaller network ( subnetwork , subnet ). ECE 128.100.11.64/26 Library 128.100.136.0/24 MIE Each subnet becomes a separate network 128.100.11.128/26
Basic Idea of Subnetting Basic Idea of Subnetting Split the interface identifier portion of an IP address into a subnet identifier and a (smaller) interface identifier. interface identifier network prefix subnet id interface id network prefix extended network prefix Then: Subnets can be freely assigned within the organization Internally, subnets are treated as separate networks Subnet structure is not visible outside the organization
Subnetmask Subnetmask For the IP configuration, the subnet id becomes part of the network prefix Device only knows about the extended network prefix The netmask of the extended network prefix is called subnetmask 128.100 11.60 CIDR notation: 128.100.11.60/24 network prefix interface identifier 128.100 11 60 Netmask notation: 128.100.11.60, 255.255.255.0 network prefix subnet id interface id extended network prefix 1 1 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 subnetmask
Example Example IP address of host: (original) network prefix: 128.100.11.60 128.100.0.0/16 Subnet number (with length 8 bit) : 11 CIDR notation of new network prefix: 128.100.11.0/24 Address of host: CIDR notation: Netmask notation: 128.100.11.60/24 128.100.11.60, 255.255.255.0
Advantages of Subnetting Advantages of Subnetting With subnetting, IP addresses use a 3-layer hierarchy: Network prefix Subnet identifier Interface identifier Subnetting reduces router complexity. Since router outside the organization do not need to know about subnetting, the complexity of routing tables at outside the organization is reduced. Flexibility: Length of the subnet mask need not be identical on all subnetworks.
Creating and Managing Subnets Creating and Managing Subnets Use of subnetting or length of the subnetmask is decided by the network administrator Subnets are created by setting the subnetmask of an IP interface Important: Subnetmasks must be set consistently
No Subnetting No Subnetting All hosts think that the other hosts are on the same network 128.143.137.32/16 subnetmask: 255.255.0.0 128.143.137.144/16 subnetmask: 255.255.0.0 128.143.71.21/16 subnetmask: 255.255.0.0 128.143.71.201/16 subnetmask: 255.255.0.0 128.143.0.0/16
With Subnetting With Subnetting Hosts with same prefix/subnetmask belong to the same network 128.143.137.32/24 subnetmask: 255.255.255.0 128.143.137.144/24 subnetmask: 255.255.255.0 128.143.71.21/24 subnetmask: 255.255.255.0 128.143.71.201/24 subnetmask: 255.255.255.0 128.143.137.0/24 Subnet 128.143.71.0/24 Subnet 128.143.0.0/16
With Subnetting With Subnetting Different subnetmasks lead to different views of the scope of the network 128.143.137.32/26 subnetmask: 255.255.255.192 128.143.137.144/26 subnetmask: 255.255.255.192 128.143.71.21/24 subnetmask: 255.255.255.0 128.143.71.201/16 subnetmask: 255.255.0.0 128.143.71.0/24 Subnet 128.143.137.0/26 Subnet 128.143.137.128/26 Subnet 128.143.0.0/16
Usage of subnet and Usage of subnet and subnetmask subnetmask Earlier, we used the term subnet even though there was no subnetting This is a convention: The terms subnet or IP subnet are used to designate an IP network Also, subnetmask and netmask are often used interchangeably 13
Every IP network is a subnet Every IP network is a subnet The term subnet for an IP network is fitting since we can view every IP network as a subnet of a larger network 0.0.0.0/0 128.0.0.0/2 Class B 128.100.0.0/16 (UofT) 128.100.11.0/24 14
