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You must know the difference between a "routed" protocol and a "routing" protocol. A routed protocol can be routed by a router, which means that it can be forwarded from one router to another. Examples of a routed protocols are IP, IPX and AppleTalk.
A routed protocol contains the data structure for a packet to be sent outside of its local network segment. This structure is called an addressing scheme. Based on the addressing scheme, you will be able to identify the network to which a host belongs, in addition to identifying that host on that network. All hosts on an internetwork (routers, servers, and workstations) can communicate with each other by using a routable protocol such as IP, IPX or AppleTalk. A routingprotocol is used to communicate routing information between routers. Its purpose is to help routers building and maintain routing tables. Examples of routing protocols are RIP, IGRP, EIGRP and OSPF(there are many others). When a router has built a complete routing table from the various routing protocols it supports, it will be able to most efficiently forward traffic via the best route.
Routed Protocols
As mentioned above, IP, IPX and AppleTalk are three common routed protocols. The exam focuses on IP since that is the predominant protocol used today. So what do you need to know about IP other than that is how all your node to node communication will occur? Make sure you know how to subnet! If you do not know how to create subnet masks to most efficiently meet a desired goal of number of subnets and hosts, you will most definitely fail the exam. Understanding how to subnet will not guarantee that you will pass this exam, but not understanding subnetting will guarantee that you fail! If you have an IP address and its subnet mask, you need to be able to identify the subnet ID of that host, the first and last useable host on that subnet, the subnet broadcast address, in addition to the number of possible subnets and hosts per subnet. If those items do not come easily to you, then you will need to brush up on these concepts. Remember you have roughly a minute per question on the exam. If it takes you more than a minute to figure the above items out, you will not finish the test in the allotted time. In addition, you will need to know how to recognize a subnet mask in its dotted decimal form (255.255.255.248) and by using a bit count (/29). You should also know which bits must be off and on in the first octet for the various classes of IP addresses (Class B would have "10" in the first two bits).
Routing Protocols
The CCNA objectives only require that you know how to configure RIP and IGRP. However, you do need to know about the three classes of routing protocols (distance vector, link state, and hybrid), and which protocol belongs to which class. RIP and IGRP are distance vector protocols. OSPF is the only link state protocol with which you need to concern yourself at this level, and EIGRP is the only hybrid protocol. Know which protocol has a lower administrative distance (RIP is 120 vs. IGRP is 100), and that static routes have a lower administrative distance if you use the defaults a static router is 1 and a directly connected router is 0. When configuring RIP or IGRP, make sure that you also know how to turn on the attached networks so that they will start sending and receiving routing updates(network xxx.xxx.0.0).
Also remember that IGRP requires the addition of an autonomous system number(AS xx). Be familiar with the metrics RIP and IGRP use in determining the best path through which to route. RIP for IP only uses hops and IGRP uses only Bandwidth and Delay be default but can also be configured to use Bandwidth, Delay, Reliability, Load, and MTU. Remember that "show ip route" displays the contents of all routing protocols in your routing table.
A routed protocol contains the data structure for a packet to be sent outside of its local network segment. This structure is called an addressing scheme. Based on the addressing scheme, you will be able to identify the network to which a host belongs, in addition to identifying that host on that network. All hosts on an internetwork (routers, servers, and workstations) can communicate with each other by using a routable protocol such as IP, IPX or AppleTalk. A routingprotocol is used to communicate routing information between routers. Its purpose is to help routers building and maintain routing tables. Examples of routing protocols are RIP, IGRP, EIGRP and OSPF(there are many others). When a router has built a complete routing table from the various routing protocols it supports, it will be able to most efficiently forward traffic via the best route.
Routed Protocols
As mentioned above, IP, IPX and AppleTalk are three common routed protocols. The exam focuses on IP since that is the predominant protocol used today. So what do you need to know about IP other than that is how all your node to node communication will occur? Make sure you know how to subnet! If you do not know how to create subnet masks to most efficiently meet a desired goal of number of subnets and hosts, you will most definitely fail the exam. Understanding how to subnet will not guarantee that you will pass this exam, but not understanding subnetting will guarantee that you fail! If you have an IP address and its subnet mask, you need to be able to identify the subnet ID of that host, the first and last useable host on that subnet, the subnet broadcast address, in addition to the number of possible subnets and hosts per subnet. If those items do not come easily to you, then you will need to brush up on these concepts. Remember you have roughly a minute per question on the exam. If it takes you more than a minute to figure the above items out, you will not finish the test in the allotted time. In addition, you will need to know how to recognize a subnet mask in its dotted decimal form (255.255.255.248) and by using a bit count (/29). You should also know which bits must be off and on in the first octet for the various classes of IP addresses (Class B would have "10" in the first two bits).
Routing Protocols
The CCNA objectives only require that you know how to configure RIP and IGRP. However, you do need to know about the three classes of routing protocols (distance vector, link state, and hybrid), and which protocol belongs to which class. RIP and IGRP are distance vector protocols. OSPF is the only link state protocol with which you need to concern yourself at this level, and EIGRP is the only hybrid protocol. Know which protocol has a lower administrative distance (RIP is 120 vs. IGRP is 100), and that static routes have a lower administrative distance if you use the defaults a static router is 1 and a directly connected router is 0. When configuring RIP or IGRP, make sure that you also know how to turn on the attached networks so that they will start sending and receiving routing updates(network xxx.xxx.0.0).
Also remember that IGRP requires the addition of an autonomous system number(AS xx). Be familiar with the metrics RIP and IGRP use in determining the best path through which to route. RIP for IP only uses hops and IGRP uses only Bandwidth and Delay be default but can also be configured to use Bandwidth, Delay, Reliability, Load, and MTU. Remember that "show ip route" displays the contents of all routing protocols in your routing table.
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