Cisco CCNA Certification Examination Tutorial: Prefix Notation
Cisco CCNA Certification Examination Tutorial: Prefix Notation
While you're preparing to cross the CCNA examination and earn this coveted Cisco certification, you've got to be totally ready for the many kinds of binary and subnetting questions Cisco might throw at you. You also should be conversant in the totally different manners wherein a subnet masks might be expressed, as within the following:
255.255.255.zero
/24
Imagine it or not, those two values are exactly the same. The first mask is written out in the more acquainted dotted decimal format, and you know by looking at those first three octets that each bit is about to "1", since the maximum worth of such an octet is 255.
The second value represents the exact same mask, only this worth is expressed in prefix notation. This explicit worth could be pronounced "slash twenty-four", and the 24 represents the variety of consecutive ones which might be set within the subnet mask.
Those of us who hate to sort numbers are notably appreciative of this, because it means you may must kind lots much less numbers to symbolize a subnet mask. In addition, it is loads easier to debate masks in prefix notation than dotted decimal. ("I thought of using a -fifty-5 -fifty-5 -fifty-five zero mask ,but then determined to make use of a two-fifty-5 two-fifty-five two-fifty-5 one-twenty-eight mask...")
Make certain you're comfortable with prefix notation earlier than taking your CCNA exam. As with Cisco documentation, you'll most certainly see masks expressed in both dotted decimal and prefix notation, and you've got to be ready to make use of the both as nicely!
RIP isn't exactly essentially the most advanced routing protocol on the CCNA exam, but that makes it easy to overlook a number of the necessary details you must remember to be able to pass the exam! That can assist you overview for the exam, listed here are only a few of these details!
RIP's default behavior is to send version 1 updates, however to just accept each version 1 and 2 routing updates.
R2(config)router rip
R2(config-router)net 172.16.0.zero
R2(config-router)^Z
R2show ip protocols
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 6 seconds
Invalid after one hundred eighty seconds, hold down 180, flushed after 240
Outgoing update filter checklist for all interfaces is
Incoming replace filter listing for all interfaces is
Redistributing: rip
Default model management: send model 1, receive any model
Interface Send Recv Key-chain
Serial0 1 1 2
By default, RIP v2 autosummarizes routing updates despatched across classful network boundaries. To disable this behavior, run no auto-abstract under the RIP process.
R1conf t
R1(config)router rip
R1(config-router)model 2
R1(config-router)no auto-summary
You don't specify a subnet masks or wildcard masks when configuring RIP - simply the classful network, even when you're operating RIP v2.
R1conf t
Enter configuration instructions, one per line. Finish with CNTL/Z.
R1(config)router rip
R1(config-router)version 2
R1(config-router)no auto-summary
R1(config-router)community 172.10.0.zero ?
Debug ip rip displays the routing updates and metrics as the commercials are despatched and requested. To see this in motion without waiting for the next often scheduled update, run clear ip route *.
R1debug ip rip
RIP protocol debugging is on
R1clear ip route *
01:16:54: RIP: sending v1 update to 255.255.255.255 through Loopback1 (1.1.1.1)
01:16:54: network 2.0.0.0, metric 2
01:16:54: community 3.0.0.0, metric 2
01:sixteen:fifty four: network 172.16.0.0, metric 1
01:sixteen:54: network 10.0.0.zero, metric 2
01:sixteen:54: RIP: sending v1 update to 255.255.255.255 via Serial0 (172.16.123.1)
01:16:fifty four: subnet 172.16.123.zero, metric 1
01:16:fifty four: community 1.0.0.zero, metric 1
01:16:54: community 2.0.0.0, metric 2
01:16:54: community 3.0.0.zero, metric 2
01:sixteen:fifty four: community 10.0.0.zero, metric 2
To see solely the routes discovered by a routing protocol, run show ip route followed by the title of the protocol:
R1show ip route rip
R 2.0.0.zero/8 [120/1] by way of 172.16.123.2, 00:00:26, Serial0
R 3.0.0.0/eight [120/1] via 172.16.13.2, 00:00:09, Serial1
[120/1] by way of 172.16.123.three, 00:00:09, Serial0
R 10.0.0.0/8 [120/1] via 172.16.13.2, 00:00:09, Serial1
[120/1] through 172.16.123.three, 00:00:09, Serial0
[120/1] by way of 172.16.123.2, 00:00:26, Serial0
And do not forget - to show off all presently running debugs, run undebug all.
R1undebug all
All potential debugging has been turned off
Do not overlook RIP and IGRP with regards to the CCNA exam. OSPF and EIGRP are more complicated to configure, however it's essential perceive how distance vector protocols work with the intention to cross the CCNA!
To pass the CCNA examination, you have to know the right way to work with IGRP and EIGRP unequal-price load balancing. Chances are you'll not see a lot IGRP in manufacturing networks anymore, but you may see a number of EIGRP, and part of nice-tuning your EIGRP community is making sure that each one paths are in use whereas allowing for various bandwidth rates.
Using the variance command is the straightforward half - it is getting the metric that is the onerous half with IGRP. With EIGRP, you simply look in the topology desk and that's it. With IGRP, you've got to run a debug to get the best metric.
The variance command is a multiplier when the value provided with the variance command is multiplied by the bottom-cost metric, it must exceed the higher-value metric in order for the higher-value path to be added.
If that sounds complicated, it's not. It's one of those issues that sounds tough, however isn't. Belief me!
In this instance, R1 has two paths to 172.23.0.zero, but is at present utilizing solely one. By trying within the IP routing desk, we've seen that the bottom-value metric for network 172.23.0.zero on R1 is 8576. This path goes by the 172.12.123.0 network. There may be one other valid path that uses the 172.12.13.zero network, however just isn't currently in use.
I 172.23.0.0/16 [100/8576] through 172.12.123.2, 00:00:fifty three, Serial0
IGRP doesn't have a "present" command that shows all valid routes to a vacation spot, as does EIGRP. The command debug ip igrp transactions will present the present metric of the routes using the 512 KBPS route.
R1debug ip igrp transactions
IGRP protocol debugging is on
19:17:51: IGRP: broadcasting request on Loopback0
19:17:fifty one: IGRP: broadcasting request on Serial0
19:17:51: IGRP: broadcasting request on Serial1
19:17:51: IGRP: received update from 172.12.13.3 on Serial1
19:17:fifty one: subnet 172.12.13.0, metric 23531 (neighbor 21531)
19:17:fifty one: subnet 172.12.123.0, metric 23531 (neighbor 8476)
19:17:51: community 1.0.0.zero, metric 24031 (neighbor 8976)
19:17:51: network 2.0.0.0, metric 22131 (neighbor 1600)
19:17:51: community 3.0.0.zero, metric 22031 (neighbor 501)
19:17:51: network 172.23.0.0, metric 21631 (neighbor 1100)
R1(config)router igrp 1
R1(config-router)variance 3
R1show ip route 172.23.0.0
Routing entry for 172.23.0.0/sixteen
Identified via "igrp 1", distance one hundred, metric 8576
Redistributing through igrp 1
Marketed by igrp 1 (self originated)
Last update from 172.12.123.2 on Serial0, 00:00:01 ago
Routing Descriptor Blocks:
* 172.12.13.3, from 172.12.13.three, 00:00:20 in the past, through Serial1
Route metric is 21631, visitors share count is 1
Total delay is 21000 microseconds, minimal
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