My Netwok Dictionary

Route summarization or aggregation,  is a mechanism used to design networks that are more flexible and perform better. With route summarization  or aggregation, in a hierarchical routing infrastructure, one route in a routing table represents many routes.

Although some routing protocols summarize only at the boundaries of major network numbers, others support route summarization (aggregation) at any bit boundary. Variable-length subnet masks enable routing protocols to summarize on bit boundaries.

In contrast, in a flat routing infrastructure, the routing table on every router in the network contains an entry for each network segment. When you use flat routing, the network IDs have no network/subnet structure and cannot be summarized.

To support route summarization, your IP addressing scheme must meet the following requirements:

• Classless routing protocols
• All IP addresses used in route summarization must share identical high-order bits.
• The length of the prefix can be any number of bits up to 32.

Advantage of Route or aggregation:

Reduces size routing tables

· Allocates an existing pool of addresses more economically

· Improve efficiency routing process more

· Lessens the load on router processor and memory resources

· Speed up network convergence.

· Isolates topology changes

· Facilitates monitoring, reporting, and troubleshooting

Calculating Summery Route

Given the networks :

100.16.0.0 /16,

100.17.0.0 /16,

100.18.0.0 /16,

100.19.0.0 /16

All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we’ll only illustrate how to convert the first and second octet from decimal to binary.

100 16 = 01100100 00010000

100 17 = 01100100 00010001

100 18 = 01100100 00010010

100 19 = 01100100 00010011

To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren’t used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.

To arrive at the summary route, write out a mask in binary with a “1″ for every bit to the left of the line we drew previously, and a “0″ for every bit to the right. That gives us the following string:

11111111 11111100 00000000 00000000

You can try Summary Route, a  free tool for calculating summery route.