Thursday, November 21, 2013

Summary route & Default route

When we learn about routing, there are something that you need to know.
That is Summary route & Default Route.

What is Summary Route?

When we configure static route, it is still fine when you configure in small network. But when we face a large network. This will become pain. which means u must configure one by one configuration for static route for every network.
This configuration would be bad for router’s memory and processor since it will need a lot of source for this configuration.
In many cases, the router doesn’t even need specific routes to each and every subnet (e.g., It would be just as happy if it knew how to get to the major network (e.g., and let another router take it from there. A router’s ability to take a group of subnetworks and summarize them as one network (i.e., one advertisement) is called route summarization.
Summary route is a method which summarize a few of route to become one route. This will make routing table more efficient.
Besides reducing the number of routing entries that a router must keep track of, route summarization can also help protect an external router from making multiple changes to its routing table due to instability within a particular subnet. For example, let’s say that you were working on a router that connected to As you were working on the router, you rebooted it several times. If you were not summarizing your routes, an external router would see each time that went away and came back. Each time, it would have to modify its own routing table. However, if your external router were receiving only a summary route (i.e.,, then it wouldn’t have to be concerned with your work on one particular subnet.
Summarization is the process of combining networks to save routing table entries. For example, it is typically more efficient to advertise instead of 254 subnets starting with going to Supernetting can save a lot of room in a routing table!
Supernetting is a technology to combine a multiple subnet.
The benefit of supernetting is:
To short routing table in router so it will save router’s memory .
You can use supernetting in a variety of networks (typically those that are large), using all types of routers and routing protocols. This section shows you how to create a supernet and then how to apply it to Cisco routers running both EIGRP and OSPF, the routing protocols usually used in larger networks.
To create a summarized entry, you gather the networks you want to combine and then write them out in binary. Let’s combine the following in an effort to save routing table entries: through through through
First, notice that the networks can easily be summarized because they are close to each other. An example of a range of networks that would be a poor choice for summarization is,, and A non close range of networks makes for an inefficient summarization entry.
Supernetting through
First, put everything into binary and then follow the bits, starting on the left and stopping when the bits do not line up. Notice where you stopped using boldface in the following: 00001010.00000001.00000000.00000000 00001010.00000010.00000000.00000000 00001010.00000011.00000000.00000000 00001010.00000100.00000000.00000000 00001010.00000101.00000000.00000000 00001010.00000110.00000000.00000000 00001010.00000111.00000000.00000000
Now, create a network number using only the boldface bits. Do not count the bits that are not in boldface. The second octet has no bits on (1s in the boldface section), so you get this:
To come up with the mask, now count all the boldface bits as 1s. Because 8 bits in the first octet and 5 bits in the second are boldface, you get this:
Supernetting through
Let’s put the network addresses into binary and use boldface for the bits starting on the left and moving to the right until they stop lining up: 10101100.0001000.00010000.00000000 10101100.0001000.00010001.00000000 10101100.0001000.00010010.00000000 10101100.0001000.00010011.00000000 10101100.0001000.00010100.00000000 10101100.0001000.00010101.00000000 10101100.0001000.00010110.00000000 10101100.0001000.00010111.00000000 10101100.0001000.00011000.00000000 10101100.0001000.00011001.00000000 10101100.0001000.00011010.00000000 10101100.0001000.00011011.00000000 10101100.0001000.00011100.00000000 10101100.0001000.00011101.00000000 10101100.0001000.00011110.00000000 10101100.0001000.00011111.00000000
Count only the boldface bits and only the bits that are on (1s) to get the following network address:
Now, create the mask by counting all the bits that are in boldface up to the point where they stop lining up. You have 9 bits in the first octet, 8 bits in the second octet, and 4 bits in the third octet. That is a /20 or this:
Try this shortcut. Take the first number and the very last number and put them into binary: 10101100.0001000.00010000.00000000 10101100.0001000.00011111.00000000
Can you see that you actually came up with the same bit numbers lining up? This is a lot easier than writing out possibly dozens of addresses.
Supernetting through
In this example, you’ll see how to summarize through By using only the first network number and the last, you’ll save a lot of time and come up with the same network address and subnet mask:
First number: = 11000000.10101000.00100000.00000000
Last number: = 11000000.10101000.00111111.00000000
Network address:
Subnet mask:
Design Considerations for Route Summarization
Keep the following information in mind when designing your network summarization points:
Only classless routing protocols support route summarization. Examples of classless routing protocols include RIPv2, EIGRP, and OSPF. Therefore, if you are working in a RIPv1 or IGRP environment, route summarization is not going to work for you.
Route summarization is most effective when the addresses have been organized in a hierarchy (i.e., hierarchical addressing). When we speak of addresses being hierarchical, we mean that the IP subnets at the bottom of the tree (i.e., the ones with the longest subnet masks) are subsets of the subnets at the top of the tree (i.e., the ones with the shortest subnet masks).

Default Route

Now let us start talk about Default route.
What is Default Route?
Default route is a rute that considered compatible to all IP address destination.
If Ip address destination from a package is not found in a routing table, router will use default route to forward those package.
Default route commonly use when there are only one rute to a network.
Step to create default routing is :
Just have 1 rute for out / 1 gateway to another network.(network stub)


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