#IP ROUTE SUMMARY CALCULATOR UPDATE#

This network will scale beautifully and have minimal performance issues (at least because of route table and routing update overhead).įIGURE 3.15 Proper planning prevents poor performance.įollowing these rules will give you one of the additional benefits of summarization as well: hiding instability in the summarized networks. It’s much like using a map to drive to a friend’s house you don’t need a great deal of detail when you are on the highway, but when you get into the residential areas, you need to know very precise information if you have a hope of finding the place.įigure 3.15 illustrates the same network after your friendly neighborhood Cisco Certified Internetwork Expert has spent the afternoon re-addressing the network and configuring summarization.

The further you get from the core, the more detail the routers need to get traffic to the correct destination network. These routers have the job of dealing with high volumes of traffic headed for all different areas of the network, so we do not want to burden them with big, highly detailed route tables. The core is where the bigger, faster, busier routers are-like the Central Office router in the previous example. The second rule is to summarize into the core of your network. Figure 3.14 shows a badly designed network that will be almost impossible to summarize because the subnets are discontiguous, with individual subnets scattered all over the system.įIGURE 3.14 Poor planning prevents proper performance. Advance planning, including making plenty of room for future growth, will give you a solid, scalable network design that readily lends itself to summarizing. The packet will get routed to the router that connects to the dead network, and dropped there. The summary is essentially saying, “I can reach the networks represented by this summary send any traffic for them through me.” If one (or more) of the networks behind the summarizing router is unavailable, traffic will be dropped-but not by the summarizing router, because the individual routes to the networks that were summarized are still valid, and have a longer match entry than the summary. This means that you will group contiguous subnets together behind the router that will summarize them-you do not want to have some subnets from a summarized group behind some other router. The first rule is to design your networks with summarization in mind, even if you don’t need it yet. Serious routing problems will happen otherwise-such as routers advertising networks inaccurately and possibly duplicating other routers’ advertisements, suboptimal or even totally incorrect routing, and severe data loss. It is important to follow a few rules and guidelines when summarizing. Know the definition and advantages of route summarization. If we take that diagram and put it into context, we can see how route summarization can reduce the number of entries in the route table, as shown in Figure 3.13. In the previous VLSM example, all the subnets for the branches and the WAN links were created from the 192.168.0.0 /24 Class C network. With more than 450,000 routes (at the time of this writing, anyway) known to major Internet routers, some way to reduce the number of entries is not only desirable, but also critical. This, of course, is an undesirable state of affairs. They get slower, drop packets, and even crash. As the network grows large, the number of individual networks listed in the IP route table becomes too big for routers to handle effectively. If subnetting is the process of lengthening the mask to create multiple smaller subnets from a single larger network, route summarization can be described as shortening the mask to include several smaller networks into one larger network address. Answer B is incorrect this describes classful routing protocols (in part). A is incorrect that is the opposite effect of summarization. Summarization enforces router authentication, preventing spurious updates from excessively loading the router.Summarization reduces the size of route tables, prevents route table instability due to flapping routes, and reduces the size of routing updates.Summarization sends all subnets as classful networks, eliminating the overhead of transmitting the mask in routing updates.It adds detail to the route tables of routers.

Why is summarization so important to an efficient routed system?

Ip route summary calculator