Many of us are familiar with the subnetting process when managing large networks. Through subnetting, we divide one network into a series of smaller sets known as subnets.
The inverse of this approach is a process called supernetting, in which we merge multiple networks to form a super network or supernet. While these methodologies differ in procedure and implementation, their goal is ultimately the same: to improve network performance and resolve the issue of IP address depletion.
Optimizing Paths With Supernetting
This guide will walk you through some of the core concepts of supernetting, its advantages, and the difference between subnetting vs. supernetting. Then we’ll discuss best practices to help you make the most of your network, including using IP management software such as SolarWinds® IP Address Manager (IPAM) to create and manage supernets.
How Does Supernetting Work?
At its most basic, the definition of supernetting is the process of combining several smaller subnets into a larger supernet. If you’re unfamiliar with the term supernetting, you may have heard it referred to as one of these other names: route summarization, route aggregation, or prefix aggregation.
Here are a few other helpful terms as we learn how supernetting works:
Internet Protocol Address
More commonly referred to as an IP address, this is a string of numbers serving as an ID and helping identify individual users on a given network. Every IP address is unique to a device, so billions of IP addresses exist today, and trillions more are available. An IP address consists of two main elements: the network address and the host address. The network address identifies which network a device is located on, while the host address identifies the host within a particular network. The division of an IP address into a network and host address is known as a subnet mask.
Subnet Mask
It divides an IP address into its two primary components—the network and host addresses.
Subnet
Also referred to as a subnetwork, a subnet is a smaller piece of a larger network and consists of the network portion of an IP address. It helps to identify the various devices using a single network.
Supernet
Sometimes referred to as a supernetwork, a supernet is when two or more IP networks are combined into one larger network using classless inter-domain routing (CIDR) notation.
CIDR
Classless inter-domain routing is a method of IP address routing used in supernetting. CIDR merges multiple subnets into one larger supernet, effectively organizing various IP addresses and optimizing address distribution.
Routing Table
Sometimes called a routing information base, a routing table is a database within a router or network containing sets of information (routes) for directing where traffic gets directed, as well as an inventory of known networks.
Network Class
There are currently five IPv4 network classes, also known as subnetworks or IP address classes. These are Class A, B, C, D, and E. Each one contains specific information for mandating how many devices can be on a single network.
Since we’re now more familiar with a few essential definitions, let’s explore how the process of supernetting works.
Optimizing Paths With Supernetting
An internet service provider (ISP) has thousands of networks with a host IP address assigned to every client. The ISP’s routers collect and trade information about the host IPs they have visibility over, creating new entries in their routing tables for each network. With thousands of networks to monitor, these routing tables can quickly become over-encumbered, putting stress on the routers due to the sheer amount of updates they must perform. A solution? Reduce the size of the routing tables and optimize paths.
By merging multiple Class C networks into a single routing entry, supernetting drastically reduces how many networks a routing table monitors, decreasing how many routes the router must share. This process is why supernetting is sometimes referred to as route summarization or route aggregation.
Supernetting consolidates several networks by taking bits from an IP address’s network ID portion and moving them to the host ID section. This movement condensesthe number of networks but raises the number of hosts.
Supernetting Rules
As you begin creating supernets, it’s important to note not all networks can be aggregated. Before you get started, keep the following rules in mind to avoid running into routing issues:
- Contiguous networks: Any network involved in the supernetting process must be contiguous (sequential)
- Equal networks: Proposed networks should all be of the same size (Class A, B, C, etc.) and be in the power of two (2^n or 2n)
- Divisible network: The first network ID should be divisible by the number of networks (size of the block) being merged
A group of networks must satisfy all three of these requirements to be successful. Using tools such as a supernet calculator can help expedite the process while reducing the possibility of error. Let’s look at some examples of how these supernetting rules are implemented.
Imagine we have two lists of networks we want to supernet; how do they measure up against these rules?
| List 1 | List 2 |
| 192.168.0.0/24 | 10.3.0.0/16 |
| 192.168.3.0/24 | 10.4.0.0/16 |
| 10.5.0.0/16 |
Contiguous:
- List 1 doesn’t pass this rule because the networks are not in sequence. The next subnet after 192.168.0.0/24 should be 192.168.1.0/24
- List 2 does pass this rule because each subnet is in sequence
Equal:
- List 1 does pass this rule because two networks need to be merged. 2 is an order of 2
- List 2 does not pass this rule because three networks need to be merged. 3 is not an order of 2
Divisible:
- List 1 does pass this rule because the first non-common octet is octet 3. The lowest IP address block is 0, and this is divisible by the block number, which is 2
- List 2 doesn’t pass this rule because the first non-common octet is octet 2. The lowest IP address block is 3. While 3 is divisible by 3, it’s not in the order of 2
Because lists 1 and 2 failed to meet the requirements of all three rules, neither of these is eligible for aggregation.
How to Implement Supernetting
Here are a few quick tips before you begin creating your first supernet:
- Because supernetting increases the number of host addresses, you’ll likely need more routers to supplement the additional load. However, they’ll not need excessive processing power to operate due to the shortening of routing tables begot by supernetting
- Consider using outside tools such as a supernet calculator or SolarWinds IPAM to streamline the process
- You will need a subnet mask, block size, CIDR value, network ID, and broadcast ID of each route
Creating a Supernet
Once you’ve ensured your networks all pass these three rules, you can begin the network aggregation by creating a subnet mask.
- Line up your IP addresses so every bit is aligned
- Compare each bit until you encounter a column where the bits don’t match up
- Set the bits to zero starting from the column where the bits did not align all the way to the end
- You can then create a subnet mask by putting ones in the positions leading up to the column where the zeroes start and copying the zeroes for the last positions
- Then, starting from the left side, count the number of zeroes equal to the number of positions in the supernet ID. For each network to the power of 2 aggregated, you’ll need one bit. For example, if you’re merging two networks, you need one bit, but if you’re aggregating eight, you’ll need three
- From here, you can translate the route into CIDR notation by using the address created in step three, then add the bits from the subnet mask created in step four
Advantages of Supernetting
One of the biggest reasons we use supernetting is to reduce the size of routing tables, but what benefit does this have? When we have a massive group of thousands of networks, the strain on routers can severely affect their performance. To avoid a router having dozens of routes, we can aggregate these. This shortening of the routing table can:
- Improve routing efficiency by increasing the speed at which routing decisions are made
- Decrease the size and frequency of routing updates
- Free up memory and reduce processing power needs
- Reduce network traffic
- Help manage your network more effectively
Another advantage of supernetting is it allows you to expand how many available addresses are on a single network.
Supernetting vs. Subnetting
While subnetting and supernetting are both methods used for managing addresses, they have several differences in how they’re implemented. For example, where subnetting breaks down a single network into smaller subnets, supernetting is the act of combining multiple networks (subnets) to form a super network or supernet. Further, subnetting is implemented using a variable length subnet mask (VLSM), whereas supernetting uses classless inter-domain routing (CIDR).
Regarding bits, subnetting involves taking bits from the host ID and adding them to the network ID of the IP address. Reversely, supernetting takes bits from the network ID and adds them to the host. This means subnet masks move bits to the right of the default mask, and supernet masks move bits to the left.
Despite their differences, ultimately, both subnetting and supernetting share the common goal of improving network speed, manageability, and overall performance.
How to Manage Supernets
Once your supernets are set up, it’s time to manage them. Manually maintaining spreadsheets or piecemealing many different solutions together will only exacerbate an already complex task and make it more time-consuming than it should be. One of the best ways to manage your supernets is by using dedicated IP management software. Doing so can help significantly improve how you manage your supernets and your network’s overall health.
We recommend using SolarWinds IP Address Manager (IPAM) to not only manage but create and edit your supernets as well. With a user-friendly drag-and-drop interface, you can quickly scan for IP addresses, upload subnets from existing spreadsheets, and create groups for your supernets.
The software also provides ways to help you track, compare, and organize data to help give you complete oversight of your entire network—all easily accessible from one centralized dashboard.
Get the Most Out of Your Supernetting With SolarWinds
Supernetting can significantly help you improve your networks’ speed, performance, and manageability. With help from SolarWinds and our suite of intuitive, feature-rich tools such as IPAM, you can create subnets and supernets, gain visibility into your networks, automate scanning of your networks for IP addresses, and much more.
If you want to explore everything SolarWinds IP Address Manager offers, download your free 30-day trial today.