Troy’s checklist for preparing for the CCNA: Objective 4 – part 2

June 25, 2009 at 4:03 pm | Posted in Cisco | Leave a comment
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Welcome to Part 2 of Objective 4: Configure, verify, and troubleshoot basic router operation and routing on Cisco routers. Don’t forget Objective 4 – Part 1.

Be able to compare and contrast the capabilities and idiosyncrasies of common routing protocols, especially:

•    RIPv1 and RIPv2
•    OSPF
•    EIGRP

You should know details like:

•    The metrics and routing algorithm that each protocol uses
•    Which protocols are classless and which are classful
•    How to enable each protocol globally and then how to enable each protocol on an interface
•    Each protocol’s default administrative distance

For example, how does OSPF select the designated router on a segment? On a related note, what determines the OSPF router ID? Can you interpret the show ip ospf neighbor command output?

Quick tutorial. Here’s how to enable OSPF and assign the router to an area:

Router(config)#router ospf 1
Router(config-router)#network 192.168.5.0 0.0.0.255 area 0 (yes, you use wildcard mask here)

Here’s how to enable EIGRP globally and enable it on an interface:

router(config) # router eigrp [autonomous-system]
router (config-router) # network x.x.x.x
router (config-router) # network y.y.y.y

Know how to set up a hyperterminal connection to a router or a switch, and the required settings for the serial connection it uses. Hint:

COM1 Properties

You should recognize the output of the common show and debug commands. You should know the mode in which the commands are issued and what each is used for. Some common examples are:

• show interfaces (allows you to determine the bandwidth of a connection)
• show ip interface brief
• show vlan
• show running-configuration
• show ip route
• show ip eigrp topology (be able to read the output and determine which routes will be included in the routing table)
• show ip route eigrp
• show ip protocols
• show cdp neighbors / show cdp neighbors detail
• debug ip rip

Being able to verify network connectivity is a stated objective of the exam. This means knowing the common troubleshooting actions, and also knowing the mechanisms that they work by (ICMP, UDP, echo request, timeout, etc.).

• traceroute
• ping
• telnet
• SSH

This also means being able to look at a router and know from the color, sequence, and stability of the lights (solid green, blinking amber, unlit) what state the router is in and what problems it may be experiencing.

Know the difference between a ping and an extended ping, and be able to recognize the differences in the output of the two commands. Know how to configure SSH on a router to protect Telnet access to the router. Remember, configuring Secure Shell (SSH) support on a Cisco router involves a minimum of three commands to configure:

• ip domain-name [domain-name]: configures the DNS of the router (global configuration mode)
• crypto key generate rsa: generates a cryptographic key to be used with SSH (global configuration mode)
• transport input ssh: allows SSH connections on the router’s VTY lines (VTY line configuration mode)

As I mentioned in Part 1, you should how to configure a default gateway on a router. (Yes, a router can have a default gateway!) It has virtually the same effect as adding a default route, but the command is different: ip default-gateway

Know how to analyze a network diagram for IP addressing problems. I covered this in an earlier blog post, but those types of problems will appear in this objective as well. On a related note, know the purpose and operation of Cisco Discovery Protocol (CDP). This incredibly handy command can be used to gather information about a router or switch that, due to an IP addressing problem, cannot be reached by a directly attached device. Since CDP operates at Layer 2 (as MAC addresses do), it will work when IP addressing is misconfigured.

Know the correct syntax to add a static route to a router, as well as how to recognize a static route in the routing table. Just so you know:

ip routeprefix mask {ip-address | interface-typeinterface-number [ip-address]} [dhcp] [distance] [namenext-hop-name] [permanent | tracknumber] [tagtag]

Here’s a quick example using the diagram below. Suppose I asked you to create a route on R1 that leads to the 192.168.110.128/26 network on R2. Assume that the address of the S0/0 interface of Router 2 is 192.35.87.5/30.

ip route example.jpeg

The command would be:

ip route 192.168.110.128 255.255.255.192 192.35.87.5

If this doesn’t make sense, here’s a reference that might help clarify things: Command reference for the ip route command

Understand the purpose of the configuration register setting on a router and how it impacts the boot process. Also know how to change it. Know what these outputs would mean:

Configuration register is 0x2142
Configuration register is 0x2102

If all of this talk about the configuration register makes you nervous, here’s a link. Chill out.
Use of the Configuration Register on All Cisco Routers

Aaaaaand… finally, we’re done with Objective 4! Keep those cards and letters coming. I’ll be back next week!

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