Cisco CCNA Exam Tutorial: Route Summarization
Cisco CCNA Exam Tutorial: Route Summarization
Making ready to cross the CCNA exam and earn this vital Cisco certification? Route summarization is just one of many many abilities you will must grasp with a purpose to earn your CCNA. Whether it is RIP model 2, OSPF, or EIGRP, the CCNA examination will demand you could flawlessly configure route summarization.
Route summarization isn't simply vital for the CCNA exam. It's a helpful talent to have in the true world as well. Accurately summarizing routes can lead to smaller routing tables which are still capable of route packets precisely - what I prefer to call "concise and full" routing tables.
The primary talent you have to have with a purpose to work with route summarization is binary math; more specifically, you have to be able to take multiple routes and come up with each an abstract route and mask to promote to downstream routers. Given the networks 100.16.0.zero /sixteen, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.zero /sixteen, may you shortly come up with both the abstract address and mask? All it is advisable to do is break the 4 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 solely illustrate find out how to convert the first and second octet from decimal to binary.
a hundred 16 = 01100100 00010000
a hundred 17 = 01100100 00010001
100 18 = 01100100 00010010
one hundred 19 = 01100100 00010011
To come up with the summary route, just work from left to right and draw a line where the 4 networks no longer have a bit in common. For these 4 networks, that time comes between the 14th and fifteenth bits. This leaves us with this string: 01100100 000100xx. All it is advisable do is convert that string back to decimal, which provides us a hundred for the primary octet and sixteen for the second. (The two x values are bits on the right aspect of the road, which aren't utilized in calculating the abstract route.) Since we all know that zero is the worth for the last two octets, the ensuing abstract community number is 100.16.0.0.
But we're not accomplished! We now must come up with the summary mask to promote together with the summary route. To reach at the summary route, write out a masks in binary with a "1" for every bit to the left of the line we drew beforehand, and a "0" for every bit to the right. That offers us the next string:
11111111 11111100 00000000 00000000
Converting that to dotted decimal, we arrive on the summary mask 255.252.0.0. The right abstract network and masks to promote are 100.16.0.zero 252.0.0.0.
For the CCNA examination, emphasis is put on realizing methods to promote these summary routes in RIPv2 and EIGRP. For each of these protocols, route summarization occurs on the interface stage - it is not configured below the protocol. On the interface that should advertise the abstract route, use the command "ip abstract-deal with". Here are examples of how the above summary route can be configured on ethernet0 in each RIPv2 and EIGRP.
R1(config-if)ip abstract-handle rip 100.16.0.zero 255.252.0.0
R1(config-if)ip summary-address eigrp a hundred 100.16.0.zero 255.252.0.zero
The primary distinction between the two is that the EIGRP command must specify the AS quantity - that is what the "one hundred" is in the midst of the EIGRP command. Since RIPv2 doesn't use AS numbers, there isn't any further value wanted in the configuration.
For OSPF, the commands differ. If you're configuring inter-space route summarization, use the "area vary" command; if you're summarizing routes which might be being redistributed into OSPF, use the abstract-deal with command underneath the OSPF routing course of on the ASBR. Neither of these are interface-degree commands.
I communicate from experience when I let you know that practice makes excellent on the CCNA exam, particularly with binary and summarization questions. The beauty of these questions is that there are not any gray areas with these questions - you either know the best way to do it otherwise you don't. And with practice and a mind for detail, you can master these expertise, cross the examination, and become a CCNA. Here's to your success!
For CCNA exam success, you had higher know what cut up horizon is, how to turn it off, and when to show it off. Knowing when to turn cut up horizon off can also be vital in manufacturing networks, as a result of it may well trigger a hub-and-spoke community to have incomplete routing tables on the spokes.
Cut up horizon exists for an excellent cause - routing loop prevention. The rule of break up horizon states that a router can not ship an commercial for a route out the identical interface that it came in on. Break up horizon is on by default on all interfaces operating RIP, IGRP, and EIGRP.
In this CCNA tutorial, R1 will serve, as the hub and R2 and R3 would be the spokes. We'll first configure EIGRP over the 172.16.123.0 /24 network, the community connecting the three routers.
R1conf t
R1(config)router eigrp 100
R1(config-router)no auto-summary
R1(config-router)community 172.12.123.zero 0.0.0.255
R2conf t
R2(config)router eigrp a hundred
R2(config-router)no auto-summary
R2(config-router)community 172.12.123.0 0.0.0.255
R3conf t
R3(config)router eigrp one hundred
R3(config-router)no auto-abstract
R3(config-router)community 172.12.123.zero 0.0.0.255
Operating present ip eigrp neighbor on R1 shows that adjacencies to R2 and R3 are up.
R1show ip eigrp neighbor
IP-EIGRP neighbors for course of a hundred
H Deal with Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
1 172.12.123.three Se0/zero 11 00:02:forty five 1 5000 0 1
zero 172.12.123.2 Se0/zero 161 00:03:01 1 5000 0 1
Each router will now advertise its loopback handle through EIGRP.
R1conf t
R1(config)router eigrp a hundred
R1(config-router)network 1.1.1.zero 0.0.0.255
R2conf t
R2(config)router eigrp a hundred
R2(config-router)network 2.2.2.zero 0.0.0.255
R3conf t
R3(config)router eigrp one hundred
R3(config-router)network 3.3.3.0 0.0.0.255
Running show ip eigrp route on each router shows that R1 has a route for each R2's and R3's loopback. R2 and R3 will solely see R1's loopback address, and never one another's. Why?
R1show ip route eigrp
2.0.0.zero/24 is subnetted, 1 subnets
D 2.2.2.0 [90/2297856] via 172.12.123.2, 00:03:19, Serial0/0
3.0.0.0/24 is subnetted, 1 subnets
D 3.3.3.zero [90/2297856] through 172.12.123.three, 00:03:04, Serial0/0
R2show ip route eigrp
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856] by way of 172.12.123.1, 00:03:40, Serial0/0.123
R3show ip route eigrp
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856] by way of 172.12.123.1, 00:05:17, Serial0/0.31
EIGRP makes use of Split Horizon by default to forestall routing loops. On this lab, though, it prevents full community reachability. R2 and R3 each form neighbor relationships with R1's Serial bodily interface. R2 advertises its loopback address to R1's Serial interface, as does R3. Break up Horizon doesn't permit a path to be advertised back out the same interface it was acquired on. This prevents R1 from promoting R2's loopback to R3, or R3's loopback to R2.
Split Horizon should be disabled to permit full network reachability on this lab. To do so, run no ip split-horizon eigrp a hundred on R1's Serial interface. When Cut up Horizon is disabled, that may cause the neighbor
relationships to fail, and then reestablish. Run present|
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