![]() Therefore, the best summary route is 172.16.12.0/22.ġ-17 Summarizing Within an Octet, for Router D in Figure 1-16 As Figure 1-17 illustrates, the first 22īits of the IP addresses from 172.16.12.0 through 172.16.15.255 are the same. Is represented by the first IP address in the block, followed by a slash,įollowed by the number of common bits. (It might be helpful to draw a vertical line marking the last matching bit inĬount the number of common bits. Locate the bit where the common pattern of digits ends. To calculate theĬonvert the addresses to binary format and align them in Highest-order (leftmost) bits that match in all the addresses. To determine the summary route on router D, determine the number of Router D in Figure 1-16 has the following networks in its routing table: This results in less CPU, memory, and bandwidth States, every router sees its 200 state subnets and 49 summarized entries States, and each of these routes is summarized before being announced to other Instead, if each state has a central site to connect it with all the other Routers would have 200 * 50 = 10,000 networks. Without route summarization, the routing table on any of those Summarization is described in RFC 1518, An Architecture for IP AddressĪs an example of the power of summarization, imagine a company that operatesĪ series of pizza shops, with 200 stores in each of the 50 states in the U.S.Įach store has a router with an Ethernet and a Frame Relay link connected to Support summarization on any bit boundary. Support summarization on any other bit boundaries. Classful routing protocols (RIPv1 and IGRP)Īutomatically summarize routes on the classful network boundary and do not IS-IS, and EIGRP) support route summarization based on subnet addresses, Classless routing protocols (such as RIPv2, OSPF, Routing protocols summarize or aggregate routes based on shared network Into groups and try to summarize the groups separately. If the number of networkĪddresses is not contiguous or not a power of 2, you can divide the addresses Must take place on binary boundaries (powers of 2). Summary masks are binary masksjust like subnet masksso summarization For example, 4,ġ6, or 512 addresses can be represented by a single routing entry because The network addresses are in contiguous blocks in powers of 2. Route summarization is most effective within a subnetted environment when Route summarization is possible only when a proper addressing plan is in Router E also saves CPU resources, because it evaluates packets againstġ-16 Routers Can Summarize to Reduce the Number of Routesįlapping is a common term used to describe intermittent interface or link Router E needs to maintain only one route and therefore saves If routerĭ summarizes the information into a single network number entry, theīandwidth is saved on the link between routers D and E. Maintain, because it is a method of representing a series of network numbers inįor example, in Figure 1-16, router D can either send four routing updateĮntries or summarize the four addresses into a single network number. Or supernetting) can reduce the number of routes that a router must Route summarization (also called route aggregation It is often problematic for routers to maintain this volume of routes in In large internetworks, hundreds, or even thousands, of network addresses canĮxist. In route summarization, a group of subnets is rolled up into a summarized With VLSM, you break a block of addresses into smaller subnets Interdomain Routing." The relationship between summarization and VLSM isĪlso examined. This sectionĭescribes summarization CIDR is covered in the later section "Classless Summarization and CIDR, you can implement a scalable network. Summarization and CIDR techniques can manage this corporate growth much Resources, memory, and bandwidth used to maintain the routing table. Network addresses in routing tables is increasing rapidly. As the result of corporate expansion and mergers, the number of subnets and
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