Grouping IP addresses into subnets and supernets is a fundamental aspect of IP address management. Enabling network admins to break up and aggregate different IP groups of their massive network address space into manageable entities, IP subnetting and supernetting have become core components of effective network address space management. The reason why creating a supernet helps the administrator utilize the available IP address space more efficiently is because of the simplified routing. These supernets are beneficial especially when there are multiple networks with limited number of IPs within each network.

Understanding the nuances of supernetting and the key differences between supernets and subnets is critical to designing and managing your IT ecosystem's network address space. A proper supernetting solution can help you address these nuances, and build network resiliency within your network. On this page, we will discuss the following:

What is a Supernet?

Supernets or supernetworks are formed by aggregating several IP subnets with contiguous (i.e., adjacent or adjoining) address ranges into one large network with a single Classless Inter-Domain Routing (CIDR) prefix. This new, shorter prefix represents the supernet and its associated subnets as one entry in the routing table entries.

For example, consider four subnets: /24 /24 /24 /24

To create a supernet for these subnets with contiguous IP prefixes, the network admins can use the prefix /21, which covers all these subnets. Note that the routing prefix of the supernet is the same as the collection of routing prefixes of its associated subnets.

Instead of advertising the routes of each of the four subnets separately, with supernetting, the routes to these subnets can be advertised as a single aggregated supernet route. This simplifies network address space management and reduces the number of routing table entries. This in turn reduces the network routing overhead, router process overhead, and routing device requirements, helping the router store information efficiently by combining several independent routes.

The process of creating a supernet is called supernetting, route aggregation, or route summarization.

Explaining route aggregation: How does a supernet work?

In enterprise networks with a massive IP address space, IP subnetting creates multiple smaller networks by lengthening the IP address mask. As the network scales, the number of subnets formed increases the number of routing table entries, eventually causing a router overload. To avoid this scenario and optimize network routing, as discussed above, the subnets should be aggregated into one supernet.

Protocol requirements for supernets to work

Supernets and route aggregation rely on classless routing to transmit the subnet mask information. The two protocols that support this are:

  • CIDR.
  • Enhanced Interior Gateway Routing Protocol (EIGRP).

Other TCP and IP routing protocols, such as Interior Gateway Routing Protocol (IGRP) and Routing Information Protocol (RIP), only support classful routing and thus do not support supernets or the route aggregation process.

Route aggregation with supernets

Among its several benefits, supernetting significantly reduces the number of routing updates required. With each route, as the packet size increases, so does the amount of bandwidth required to transfer it, leaving less bandwidth available for other data transfers. Supernetting avoids this hassle by following the three processes of:

  • Supernet advertising: The network administrators plan and design the IP address space into smaller subnetworks and summarize their routes into the larger supernet. The router advertises this summarized route to populate the routing table entries of the neighboring routers.
  • Supernet routing: During the network's IP-based data transfer, when a router receives a data packet with the summarized supernet prefix as the destination address, it uses the prefix's routing table entry to forward the packet to its next hop.
  • Supernet to subnet routing: If the destination address is within one of the original subnets aggregated into the supernet, the router will perform an additional lookup to determine the next hop for the specific subnet.

Only Supernetting your network is not enough, it has to be managed constantly to make sure there are no network outages. This can be done by using a supernetting tool like ManageEngine OpUtils, which helps you manage the supernets in your organization efficiently.

Summarizing routes: How to supernet your network

As discussed earlier, to create a supernet solution, you need to group multiple smaller subnets into one larger network. But to effectively do this, it is necessary to have a good understanding of how IP subnetting and IP addressing works. Network admins can create supernets in three simple steps:

Step 1: Decide on the required subnets

Prerequisite: The subnets should be contiguous.

Not all subnets need to be aggregated into a supernet. Network admins are advised to carefully analyze their network address space and routing loads before creating supernets.

Let us assume that an organization has the following four subnets and that the network admin has choosen to aggregate them into a supernet: /24 /24 /24 /24

Step 2: Identify the supernet's network ID

Translate the numerical IP addresses of the subnets' IDs into their binary form.

This translates the subnets above to the following: /24 = 00001010.00001100.00000001.00000000 /24 = 00001010.00001100.00000010.00000000 /24 = 00001010.00001100.00000011.00000000 /24 = 00001010.00001100.00000100.00000000

Now, in the binary form, find the longest matching bits from left to right and add zeros for the remaining bits. Adding zeros converts the network bits of the aggregated subnets into host bits.

In this case, the result would be 00001010.00001100.00000000.00000000. Which translates to the following network ID: This is the summarized route of the supernet that will be advertised.

Step 3: Calculate the supernet's new subnet mask

To identify the mask, replace the matching bits identified in Step 2 with ones.

In this case, it would be 11111111.11111111.11111000.00000000. Which translates to the following new mask: Thus, our new summarized route or supernet address is / 21.

Supernetting vs. IP subnetting: 7 key differences

Subnetting and supernetting are two different techniques used in IP networking to optimize IP address usage and routing efficiency, respectively. However, there are significant differences between the two. Here are 7 key differences between subnetting and supernetting:

Factor Subnets Supernets
1. Core purpose Decrease address depletion Improve routing efficiency
2. Network segmentation Segment the IP address space into smaller, more manageable networks Aggregate smaller networks to be represented as a single networking entity
3. IP address bits Increase the network's address bits by shifting the network mask bits towards the right Increase the host's address bits by shifting the network mask bits towards the left
4. IP management techniques Rely on variable-length subnet mask (VLSM) and fixed-length subnet mask (FLSM) techniques Rely on the CIDR technique
5. Addressing restrictions Require all IP-associated devices within the subnet to use the same subnet mask
  • Cannot work between different IP address classes
  • Cannot work with non-contiguous subnets
6. Security Can limit network communication between different devices by creating several isolated subnets Do not offer this capability
7. Use cases
  • Are recommended when limiting network congestion is the primary requirement
  • Are often used in LANs
  • Are recommended when optimizing the routing process is the primary requirement
  • Are often used in WANs

Pros and cons of IP supernets

Before choosing to create supernets, it is important to carefully evaluate their pros and cons with respect to your network. While supernets offer several benefits, careful planning and choosing a powerful supernet solution is required to avoid their potential drawbacks.

Advantages of supernets

  • Routing optimization: Processing large routing tables for each packet that enters increases the router process overhead and CPU consumption. By dramatically reducing the number of advertised routes, supernetting significantly optimizes network routing and the router performance.
  • Simplified IP address management: With supernets, network admins can manage multiple IP address groups as a single entity, thereby simplifying network design and IP monitoring. Also, the grouping capability of supernets offers more efficient use of IP addresses, which might have otherwise been wasted in a network with smaller subnets.
  • Flexibility in IP address grouping: Supernetting offers more flexibility in network designing and grouping with a comprehensive network mask that can represent all associated subnets. Also, since the supernet's size can be calculated and recalculated according to the number of subnets being associated with it, it offers better network scalability with limited routing update requirements.

In a nutshell, supernet provides a scalable and efficient way to manage IP addresses and optimize network routing.

Disadvantages of supernets

  • Increased risk of network outages: Since a supernet represents all its associated subnets with one routing table entry, any issue in the table updates or routing process can affect all the associated subnets. This increases the risk of network outages for all associated subnets, even if the cause of the outage pertains to just one of the associated subnets.
  • Complicated troubleshooting: When a network issue arises, it can be more difficult to troubleshoot it when using supernets as there are more IP addresses and subnets to examine. Also, supernetting requires careful planning to ensure that routing tables do not become too large or unwieldy.
  • Increased security risks: Subnets offer security capabilities such as subnet isolation. However, aggregating subnets with different security configurations into a supernet increases the security risks by making it easier for unauthorized access to occur.

Supernetting best practices

  • Understand your IT requirements: Supernetting is best suited for enterprise-level WANs that have a large number of subnets that need to be aggregated. Also, it is important to ensure proper routing protocol support as not all routing protocols support supernets.
  • Select subnets carefully: Aggregating unnecessary subnets and overlapping subnets can lead to routing complexities and issues in the network. Ensure that only the required subnets are aggregated into supernets. This makes the resulting supernet efficient and easily manageable.
  • Plan ahead for scalability: Supernets are often not a set-and-forget endeavor. Ensure that the subnet mask for the supernet has enough IP addresses to accommodate future subnet aggregations.
  • Follow a security-first approach: Avoid aggregating subnets with different security requirements into one supernet.
  • Use classless addressing and limit the supernet size: Classelss addressing offers better flexibility in supernet design than classful addressing. However, unplanned supernetting can lead to larger routing tables, which can negatively impact routing performance. To avoid this, limit the size of supernets to no more than /22.
  • Ensure real-time supernet monitoring: Stay in the know about your supernet status in real time. Tracking the availability of the associated subnets helps you enhance capacity planning and stay ahead of issues such as IP address conflicts that can disrupt network connectivity for end users.

Managing supernets with OpUtils: Centralized, simple, effective

ManageEngine OpUtils' is a supernet tool that enables you to leverage a comprehensive IP address manager and advanced IP scanner to track, monitor, and manage your supernets with ease. This holistic supernet monitor tool offers in-depth insights into all your network supernets and associated subnets, with real-time insights into the IP utilization, status, and availability metrics.

What is Supernet? - ManageEngine OpUtils

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