Configure IP addresses, subnet masks, and gateway addresses on routers and hosts

Configuring the IP address and subnet mask on a Cisco router is done with one easy command.

The gateway address, also referred to as a default route, is the IP address of the next step toward an IP address in a different subnet that isn’t provided by some other route. Setting the default route on a Cisco router is also an easy single commnd.

Configuring these values on a host (as far as the exam is concerned) is more about knowing what values to configure than how to configure them (every operating system has different methods for setting these values anyway). Understanding subnets is the most imporatant aspect of this objective point. Make sure you can tell which IP addresses in a list are included in a subnet and which are outside of a subnet. Keep in mind that the default route for a host must be in the same subnet as the host’s IP address.

Configure routing protocols given user requirements

The principle job of a router is to take in a packet, figure out where to send it next to get it closer to its destination, and send it out the appropriate interface. To do this, a router is configured with or builds a routing table containing network addresses and how to route to those networks (either by IP address or router interface). The majority of this objective, and a good part of the CCNA exam, is related to configuring a router to dynamically build the routing table.

There are four routing protocols in addition to static routing that you need to be comfortable with, all with their own jargon and configuration steps. Ultimately, the configuration steps for each are rather simple. The trick is understanding when to use one over the others and remembering the configuration nuances of each.

Multiple routing protocols may be in use at the same time on the same router. Each routing protocol is assigned an administrative distance, a number determining the reliability of the information. When multiple routes from different protocols are available to a destination, the router will select the route from the protocol with the lowest administrative distance.

Static Routes

Administrative distance: 1
Routing protocols are either static or dynamic. Static routes change only when manually edited. Changes to the network will not be reflected in the routing table of a router. Static routing alone is rarely used in large networks because of the administrative overhead, but their ease of configuration make them attractive for small networks with few or rarely changing routes or between networks connected by an expensive or slow WAN link. Static routes require no conversation between routers, so utilize no bandwidth. All dynamic routing protocols require some exchange of routing information between routers, thus utilizing the bandwidth between them.

Configuring a static route is discussed here.

Default route

The “gateway of last resort” is another term for the default route, an IP address that serves as the route used when a destination is not included in the routing table. The default route is a specialized form of static route and it’s configuration is similar.

Dynamic routing

Static routing does not scale well as networks increase in size. Dynamic routing protocols provide the scalability required to support large networks. There are numerous protocols, but for the exam it is sufficient to know RIP, IGRP, EIGRP, and OSPF. Each routing protocol has its own merits and configuration steps.

For each of these protocols, the important information is highlighted in the text (the benefits and drawbacks of each), a link is provided for basic configuration instructions, and another link for detailed information about the protocol. It is recommended not to get too deep into the behind-the-scenes information about the protocols. The important information here is to be able to select the appropriate routing protocol based on simplistic scenarios and to be able to perform the few commands necessary to configure each protocol. Avoid links to the more involved whitepapers on these topics (until you’re going for your CCNP.. or maybe CCIE).

RIP

Administrative distance: 120
Distance-vector (maximum hop count 15)
Route with fewest hops wins
High bandwidth use (full routing table updates every 30 seconds)
Configuration steps
Detailed information

OSPF

Administrative distance: 110
Configuration steps
Detailed information

IGRP

Administrative distance: 100
Proprietary (developed by Cisco)
Distance-vector (maximum hop-count 255)
Classful protocol (no subnet masks)
Configuration steps
Detailed information

EIGRP

Administrative distance: 90
Distance-vector and link-state hybrid
Classless protocol (supports variable length subnet masks)
Configuration steps
Detailed information

Develop an access list to meet user specifications

Implementing access lists comes down the road in objective 2.10. For now, it is only important to understand the types of access lists, their uses, and their overall design.

NetworkClue has an overview of access lists that provides a good starting point.

A longer article called Demystifying Cisco Access Control Lists provides a great and more thorough review of access lists. The Anatomy of an Access List PDF referenced on the first page is an awesome reference and is definitely printer worthy. The article gets into the how which we will revisit down the road, but it won’t hurt to read through it now.

Design a simple internetwork using Cisco technology

Cisco provides an introduction to WAN technologies which lightly covers the basics of internetworking sufficiently for this objective. As you progress through preparation for the CCNA, you’ll cover more advanced WAN topics that will fill in the details of more open-ended objectives such as this one.

Select an appropriate routing protocol based on user requirements

David Davis has a concise review of selecting routing protocols describing their strengths and weaknesses, their ideal topologies, and a brief description of how they work.

Design an IP addressing scheme to meet design requirements

Cisco has a IP addressing and subnetting for new users document that provides a rough overview of the subject.

This forum post describes two techniques for working with subnets, one one paper with charts (which he says is good for the CCNA and I agree), and another which can be done in your head which is good for real world work after getting some experience.

Design a simple LAN using Cisco Technology

networkdictionary.com has a very concise description of the Ethernet-related LAN technologies covered in this objective.