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Supernetting is synonymous with Classless Inter-Domain Routing (CIDR) although CIDR is rather just the concept that is implemented when subnetting or supernetting. The process of supernetting is also known as route aggregation or route summarization.

Overview

In Internet networking terminology, a supernet is a block of contiguous subnetworks addressed as a single subnet. Supernets always have masks that are smaller than the classful mask, otherwise it isn't a supernet. One purpose of this is to free up millions of wasted IP addresses on the Internet that classful addressing consumed.

Supernetting alleviates some of the issues with the original classful addressing scheme for IP addresses by allowing multiple networks address ranges to be combined, either to create a single larger network, or just for route aggregation to keep the "Internet Routing Table" (or any routing table) from growing too large.

Supernetting refers to the process of aggregating multiple routes of Internet-connected routers, thus saving space in the routing table and speeding up packet routing. An analogy would be on a U.S. interstate highway, where a single sign points in the direction of three to five major cities. As you draw nearer to your destination, the signs start separating for the distinct paths to each city. The same principle can be applied to supernetting .

Supernetting, also known as route aggregation or route summarization, summarizes a group of routes into a single route advertisement. Route summarization can be used as a powerful tool in a networking environment. The demand for increased network capabilities has resulted from corporate expansions and mergers. The number of subnets and network addresses contained in routing table is rapidly increasing based on these expansions. This growth has had a negative impact on CPU resources, bandwidth, and memory used to maintain the routing tables. Therefore, route summarization was introduced as a way to reduce the size of network routing tables.

If configured properly, supernetting can reduce the latency associated with router hop, since the average speed for routing table lookup will be increased due to the reduced number of entries. The overhead for routing protocols can also be reduced since fewer routing entries are being advertised.

Another advantage of using supernetting in large, complex networks is that it can isolate topology changes from other routers. This can aid in improving the stability of the network by limiting the propagation of routing traffic after a network link goes down. For example, if a router only advertises a summary route to the next router hop, then it will not advertise any changes to specific subnets within the summarized range. This can significantly reduce any unnecessary routing updates following a topology change. Hence, increasing the speed of convergence and allowing for a more stable environment.

Protocol requiremetns

For supernetting to work, you must be using static routing everywhere or be using a routing protocol which supports classless routing, such as RIPv2 or OSPF (or BGP for Exterior Routing) which can carry subnet mask information with the routing update. The older RIPv1 (or EGP for Exterior Routing) protocol only understands classful addressing, and therefore cannot transmit subnet mask information.

EIGRP is also a Classless Routing Protocol capable of support for CIDR or VLSM (Variable Length Subnet Masking). By default EIGRP will summarize the routes within the routing table and forward these summarized routes to its peers. This can be disastrous within heterogeneous routing environments if VLSM has been used with Discontiguous Subnets and therefore Auto-Summarization should be disabled unless VLSM has been carefully designed and implemented.

The family of Classfull Routing Protocols are RIPv1, and IGRP - these protocols can not support CIDR as they do not have the ability to include subnet info within the Routing Updates.

The Family of Classless Routing Protocols are RIPv2, OSPF, EIGRP and BGP. EIGRP can handle multiple Routed Protocols such as IPX and Appletalk. RTP (Reliable Transport Protocol) is used by EIGRP as it's layer 4 protocol as opposed to TCP. This keeps EIGRP Protocol Independent because RTP is not native to THE TCP/IP ip stack like TCP.

Examples

Let's take a class B mask of 255.255.0.0 - If we borrow 2 network bits, the mask changes to 255.252.0.0, this is called Supernetting. If on the other hand we borrow two host bits, the mask changes to 255.255.192.0, this is called subnetting.

This same method can be used on class A and C addresses.

As an example of how supernetting can be used as a powerful tool in a networking environment imagine a company that operates 150 accounting services in each of the 50 states and each accounting office has a router and frame relay link connected to its corporate office. Without supernetting, the routing table on any given router would have to maintain 150 routers times 50 states = 7,500 different networks. However, if supernetting is implemented, then each state would have a centralized site to connect it with all other offices. Since each router is summarized before being advertised to other states, then every router will only see its own subnets and 49 summarized entries representing other states. This would create less stress on the router’s CPU, memory, and bandwidth.

In order to determine the summary route on a router, you must first decide the number of highest-order bits that match in all addresses. See the following example which shows the process of calculating a summary route.

In the table below, Router A has the following networks in its routing table:

192.168.98.0
192.168.99.0
192.168.100.0
192.168.101.0
192.168.102.0
192.168.105.0

First of all, you must convert the addresses to binary format and align them in a list as shown in the table below.

Address	First Octet	Second Octet	Third Octet
192.168.98.0	11000000	10101000	01100010
192.168.99.0	11000000	10101000	01100011
192.168.100.0	11000000	10101000	01100100
192.168.101.0	11000000	10101000	01100101
192.168.102.0	11000000	10101000	01100110
192.168.105.0	11000000	10101000	01101001

Second, locate the bits where the common pattern of digits ends (those in red). Lastly, count the number of common bits. The summary route should be your lowest IP address, followed by a slash, followed by the number of common bits.

Summarized route is 192.168.96.0/20 (or 255.255.240.0)

192.168.96.0	11000000	10101000	01100000	00000000

As you can see, the first 20 bits of the IP address are the same. Hence, the best summary route can be advertised as 192.168.96.0/20. For supernetting to work properly, multiple IP addresses must share the same highest-order bits and should only be implemented within classless routing protocols such as EIGRP, OSPF, RIP v.2, IS-IS for IP, and BGP.

In some cases, this feature may not be feasible. For example, in RIP v.1 is a classful routing protocol that automatically summarizes based on class when advertising across a major network boundary. Automatic supernetting can potentially cause problems if summarization occurs at more than one point in the network since the summarized routes may be in conflict. When this occurs, a router receives identical summary routes from different directions. This can lead to serious connectivity issues.

External links

The Supernetting/CIDR Chart

This computer networking article is a stub. You can help Wikipedia by expanding it.

@@ Line 1: / Line 1: @@
-'''Supernetting''' is synonymous with '''[[Classless Inter-Domain Routing]] (CIDR)''' although CIDR is rather just the concept that is implemented when '''subnetting''' or '''supernetting'''.
+'''Supernetting''' is synonymous with '''[[Classless Inter-Domain Routing]] (CIDR)''' although CIDR is rather just the concept that is implemented when '''subnetting''' or '''supernetting'''. The process of supernetting is also known as ''route aggregation'' or ''route summarization''.
+== Overview ==
 In [[Internet]] networking terminology,  a '''supernet''' is a block of contiguous [[subnetwork]]s addressed as a single subnet. Supernets always have masks that are smaller than the classful mask, otherwise it isn't a supernet.  One purpose of this is to free up millions of wasted IP addresses on the Internet that [[classful addressing]] consumed.
 Supernetting alleviates some of the issues with the original [[classful addressing]] scheme for [[IP address]]es by allowing multiple networks address ranges to be combined, either to create a single larger network, or just for [[route aggregation]] to keep the "Internet Routing Table" (or any [[routing table]]) from growing too large.
+Supernetting refers to the process of aggregating multiple routes of Internet-connected [[router]]s, thus saving space in the [[routing table]] and speeding up packet routing. An analogy would be on a U.S. interstate highway, where a single sign points in the direction of three to five major cities. As you draw nearer to your destination, the signs start separating for the distinct paths to each city. The same principle can be applied to supernetting .
+Supernetting, also known as ''route aggregation'' or ''route summarization'', summarizes a group of routes into a single route advertisement. Route summarization can be used as a powerful tool in a networking environment. The demand for increased network capabilities has resulted from corporate expansions and mergers. The number of subnets and network addresses contained in routing table is rapidly increasing based on these expansions. This growth has had a negative impact on CPU resources, bandwidth, and memory used to maintain the routing tables. Therefore, route summarization was introduced as a way to reduce the size of network routing tables.
+If configured properly, supernetting can reduce the latency associated with router hop, since the average speed for routing table lookup will be increased due to the reduced number of entries. The overhead for [[routing protocol]]s can also be reduced since fewer routing entries are being advertised.
+Another advantage of using supernetting in large, complex networks is that it can isolate topology changes from other routers. This can aid in improving the stability of the network by limiting the propagation of routing traffic after a network link goes down. For example, if a router only advertises a summary route to the next router hop, then it will not advertise any changes to specific subnets within the summarized range. This can significantly reduce any unnecessary routing updates following a topology change. Hence, increasing the speed of convergence and allowing for a more stable environment.
+== Protocol requiremetns ==
 For supernetting to work, you must be using static [[routing]] everywhere or be using a routing protocol which supports classless routing, such as [[RIPv2]] or [[Open Shortest Path First|OSPF]] (or [[BGP]] for Exterior Routing) which can carry subnet mask information with the routing update. The older [[RIPv1]] (or [[EGP]] for Exterior Routing) protocol only understands classful addressing, and therefore cannot transmit subnet mask information.
@@ Line 13: / Line 25: @@
 The Family of Classless Routing Protocols are '''RIPv2''', '''OSPF''', '''EIGRP''' and '''BGP'''. '''EIGRP''' can handle multiple Routed Protocols such as '''IPX''' and '''Appletalk'''. '''RTP''' (Reliable Transport Protocol) is used by '''EIGRP''' as it's layer 4 protocol as opposed to TCP. This keeps EIGRP '''Protocol''' '''Independent''' because RTP is not native to THE TCP/IP ip stack like TCP.
+== Examples ==
-Another way to look at supernetting is:
 Let's take a class B mask of 255.255.0.0 - If we borrow 2 network bits, the mask changes to 255.252.0.0, this is called Supernetting. If on the other hand we borrow two host bits, the mask changes to 255.255.192.0, this is called subnetting.
@@ Line 19: / Line 31: @@
 This same method can be used on class A and C addresses.
+As an example of how supernetting can be used as a powerful tool in a networking environment imagine a company that operates 150 accounting services in each of the 50 states and each accounting office has a router and frame relay link connected to its corporate office. Without supernetting, the routing table on any given router would have to maintain 150 routers times 50 states = 7,500 different networks. However, if supernetting is implemented, then each state would have a centralized site to connect it with all other offices. Since each router is summarized before being advertised to other states, then every router will only see its own subnets and 49 summarized entries representing other states. This would create less stress on the router’s CPU, memory, and bandwidth.
-== Content from 'Route summarization' ==
-Route summarization refers to the process of aggregating multiple routes of Internet-connected [[router]]s, thus saving space in the [[routing table]] and speeding up packet routing. An analogy would be on a U.S. interstate highway, where a single sign points in the direction of three to five major cities. As you draw nearer to your destination, the signs start separating for the distinct paths to each city. The same principle can be applied to route summarization.
-Route summarization, also known as [[route aggregation]], summarizes a group of routes into a single route advertisement. Route summarization can be used as a powerful tool in a networking environment. The demand for increased network capabilities has resulted from corporate expansions and mergers. The number of subnets and network addresses contained in routing table is rapidly increasing based on these expansions. This growth has had a negative impact on CPU resources, bandwidth, and memory used to maintain the routing tables. Therefore, route summarization was introduced as a way to reduce the size of network routing tables.
-If configured properly, route summarization can reduce the latency associated with router hop, since the average speed for routing table lookup will be increased due to the reduced number of entries. The overhead for [[routing protocol]]s can also be reduced since fewer routing entries are being advertised.
-Another advantage of using route summarization in large, complex networks is that it can isolate topology changes from other routers. This can aid in improving the stability of the network by limiting the propagation of routing traffic after a network link goes down. For example, if a router only advertises a summary route to the next router hop, then it will not advertise any changes to specific subnets within the summarized range. This can significantly reduce any unnecessary routing updates following a topology change. Hence, increasing the speed of convergence and allowing for a more stable environment.
-As an example of how summarization can be used as a powerful tool in a networking environment imagine a company that operates 150 accounting services in each of the 50 states and each accounting office has a router and frame relay link connected to its corporate office. Without route summarization, the routing table on any given router would have to maintain 150 routers times 50 states = 7,500 different networks. However, if route summarization is implemented, then each state would have a centralized site to connect it with all other offices. Since each router is summarized before being advertised to other states, then every router will only see its own subnets and 49 summarized entries representing other states. This would create less stress on the router’s CPU, memory, and bandwidth.
 In order to determine the summary route on a router, you must first decide the number of highest-order bits that match in all addresses. See the following example which shows the process of calculating a summary route.
@@ Line 104: / Line 106: @@
 As you can see, the first 20 bits of the IP address are the same. Hence, the best summary route can be advertised as 192.168.96.0/20.
-For summarization to work properly, multiple IP addresses must share the same highest-order bits and should only be implemented within classless routing protocols such as EIGRP, OSPF, RIP v.2, IS-IS for IP, and BGP.
+For supernetting to work properly, multiple IP addresses must share the same highest-order bits and should only be implemented within classless routing protocols such as EIGRP, OSPF, RIP v.2, IS-IS for IP, and BGP.
-In some cases, this feature may not be feasible. For example, in RIP v.1 is a classful routing protocol that automatically summarizes based on class when advertising across a major network boundary. Automatic route summarization can potentially cause problems if summarization occurs at more than one point in the network since the summarized routes may be in conflict. When this occurs, a router receives identical summary routes from different directions. This can lead to serious connectivity issues.
-[[Category:Network performance]]
-[[Category:Routing]]
-== Content from Route aggregation ==
-'''Route aggregation''' is a technique that is used to conserve the problem of address space exhaustion as well as to limit the amount of routing information being advertised. The term Classless Inter-Domain Routing (CIDR) is a route aggregation technique that was used in the early 90's to deal with these problems. From a conceptual point of view, CIDR will take a block of contiguous class C addresses and represent them as a pair of numerical terms:
-(network address, count)
-This pair shows the smallest network address in the block, and the count indicates the number of networks in the block. For example:
-(192.168.1.0, 4) = 192.168.1.0, 192.168.2.0, 192.168.3.0, 192.168.4.0.
-The pair represents a total of 4 network addresses. reduces the size of routing tables. In practice, CIDR does not restrict network numbers to class C networks nor does it use a count to specify block sizes. Instead CIDR requires the block of addresses to be a power of 2, and it uses a bit mask to identify the size of the block.
-Example:
-An ISP is assigned a block of [[IP address]]es by a regional Internet registry (RIR); for example they may receive the address range of 172.1.0.0 to 172.1.255.255.  They could then assign [[subnetwork|subnet]]s to each of their downstream providers, e.g.: ''Customer A'' will have the range 172.1.1.0 to 172.1.1.255, ''Customer B'' would receive the range 172.1.2.0 to 172.1.2.255 and ''Customer C'' would receive the range 172.1.3.0 to 172.1.3.255 and so on.  Instead of an entry for each of the subnets 172.1.1.x and 172.1.2.x etc, the ISP could aggregate the entire 172.1.x.x address range and advertise the network 172.1.0.0/16 on the Internet community, which would reduce the number of entries in the global [[routing table]].
-Comer, Douglas E. (2006). Internetworking with TCP/IP, 5, Prentice Hall: Upper Saddle River, NJ.
-[[Category:Routing protocols]]
-[[id:Route aggregation]]
+In some cases, this feature may not be feasible. For example, in RIP v.1 is a classful routing protocol that automatically summarizes based on class when advertising across a major network boundary. Automatic supernetting can potentially cause problems if summarization occurs at more than one point in the network since the summarized routes may be in conflict. When this occurs, a router receives identical summary routes from different directions. This can lead to serious connectivity issues.
 == External links ==
 * [http://www.firewall.cx/supernetting-chart.php The Supernetting/CIDR Chart]
+[[Category:Network performance]]
+[[Category:Routing protocols]]
 [[Category:Internet terminology]]
 [[Category:Routing]]