In preparation of our CCNA exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNA exam. So to assist you, below we will discuss Cisco Router Basics.

Basics Of Cisco Routers

Introduction

Cisco is well known for its routers and switches. I must admit they are very good quality products and once they are up and running, you can pretty much forget about them because they rarely fail.

We are going to focus on routers here since that’s the reason you clicked on this page !

Cisco has a number of different routers, amongst them are the popular 1600 series, 2500 series and 2600 series. The ranges start from the 600 series and go up to the 12000 series (now we are talking about a lot of money).

Below are a few of the routers mentioned :

All the above equipment runs special software called the Cisco Internetwork Operating System or IOS. This is the kernel of Cisco routers and most switches. Cisco has created what they call Cisco Fusion, which is supposed to make all Cisco devices run the same operating system.

We are going to begin with the basic components which make up a Cisco router (and switches) and I will be explaining what they are used for, so grab that tea or coffee and let’s get going !

The basic components of any Cisco router are :

Interfaces The Processor (CPU) Internetwork Operating System (IOS) RXBoot Image RAM NVRAM ROM Flash memory Configuration Register Now I just hope you haven’t looked at the list and thought “Stuff this, it looks hard and complicated” because I assure you, it’s less painful than you might think ! In fact, once you read it a couple of times, you will find all of it easy to remember and understand.

Interfaces

These allow us to use the router ! The interfaces are the various serial ports or ethernet ports which we use to connect the router to our LAN. There are a number of different interfaces but we are going to hit the basic stuff only.

Here are some of the names Cisco has given some of the interfaces: E0 (first Ethernet interface), E1 (second Ethernet interface). S0 (first Serial interface), S1 (second Serial interface), BRI 0 (first B channel for Basic ISDN) and BRI 1 (second B channel for Basic ISDN).

In the picture below you can see the back view of a Cisco router, you can clearly see the various interfaces it has:(we are only looking at ISDN routers)

You can see that it even has phone sockets ! Yes, that’s normal since you have to connect a digital phone to an ISDN line and since this is an ISDN router, it has this option with the router. I should, however, explain that you don’t normally get routers with ISDN S/T and ISDN U interfaces together. Any ISDN line requires a Network Terminator (NT) installed at the customer’s premises and you connect your equipment after this terminator. An ISDN S/T interface doesn’t have the NT device built in, so you need an NT device in order to use the router. On the other hand, an ISDN U interface has the NT device built in to the router.

Check the picture below to see how to connect the router using the different ISDN interfaces:

Apart from the ISDN interfaces, we also have an Ethernet interface that connects to a device in your LAN, usually a hub or a computer. If connecting to a Hub uplink port, then you set the small switch to “Hub”, but if connecting to a PC, you need to set it to “Node”. This switch will simply convert the cable from a straight through (hub) to a x- over (Node):

The Config or Console port is a Female DB9 connector which you connect, using a special cable, to your computers serial port and it allows you to directly configure the router.

The Processor (CPU)

All Cisco routers have a main processor that takes care of the main functions of the router. The CPU generates interrupts (IRQ) in order to communicate with the other electronic components in the router. The Cisco routers utilise Motorola RISC processors. Usually the CPU utilisation on a normal router wouldn’t exceed 20 %.

The IOS

The IOS is the main operating system on which the router runs. The IOS is loaded upon the router’s bootup. It usually is around 2 to 5MB in size, but can be a lot larger depending on the router series. The IOS is currently on version 12, and Cisco periodically releases minor versions every couple of months e.g 12.1 , 12.3 etc. to fix small bugs and also add extra functionality.

The IOS gives the router its various capabilities and can also be updated or downloaded from the router for backup purposes. On the 1600 series and above, you get the IOS on a PCMCIA Flash card. This Flash card then plugs into a slot located at the back of the router and the router loads the IOS “image” (as they call it). Usually this image of the operating system is compressed so the router must decompress the image in its memory in order to use it.

The IOS is one of the most critical parts of the router, without it the router is pretty much useless. Just keep in mind that it is not necessary to have a flash card (as described above with the 1600 series router) in order to load the IOS. You can actually configure most Cisco routers to load the image off a network tftp server or from another router which might hold multiple IOS images for different routers, in which case it will have a large capacity Flash card to store these images.

The RXBoot Image

The RXBoot image (also known as Bootloader) is nothing more than a “cut-down” version of the IOS located in the router’s ROM (Read Only Memory). If you had no Flash card to load the IOS from, you can configure the router to load the RXBoot image, which would give you the ability to perform minor maintenance operations and bring various interfaces up or down.

The RAM

The RAM, or Random Access Memory, is where the router loads the IOS and the configuration file. It works exactly the same way as your computer’s memory, where the operating system loads along with all the various programs. The amount of RAM your router needs is subject to the size of the IOS image and configuration file you have. To give you an indication of the amounts of RAM we are talking about, in most cases, smaller routers (up to the 1600 series) are happy with 12 to 16 MB while the bigger routers with larger IOS images would need around 32 to 64 MB of memory. Routing tables are also stored in the system’s RAM so if you have large and complex routing tables, you will obviously need more RAM ! When I tried to upgrade the RAM on a Cisco 1600 router, I unscrewed the case and opened it and was amazed to find a 72 pin SIMM slot where you needed to attach the extra RAM. For those who don’t know what a 72 pin SIMM is, it’s basically the type of RAM the older Pentium socket 7 CPUs took, back in ‘95. This type of memory was replaced by today’s standard 168 pin DIMMs or SDRAM.

The NVRAM (Non-Volatile RAM)

The NVRAM is a special memory place where the router holds its configuration. When you configure a router and then save the configuration, it is stored in the NVRAM. This memory is not big at all when compared with the system’s RAM. On a Cisco 1600 series, it is only 8 KB while on bigger routers, like the 2600 series, it is 32 KB. Normally, when a router starts up, after it loads the IOS image it will look into the NVRAM and load the configuration file in order to configure the router. The NVRAM is not erased when the router is reloaded or even switched off.

ROM (Read Only Memory)

The ROM is used to start and maintain the router. It contains some code, like the Bootstrap and POST, which helps the router do some basic tests and bootup when it’s powered on or reloaded. You cannot alter any of the code in this memory as it has been set from the factory and is Read Only.

Flash Memory

The Flash memory is that card I spoke about in the IOS section. All it is, is an EEPROM (Electrical Eraseable Programmable Read Only Memory) card. It fits into a special slot normally located at the back of the router and contains nothing more than the IOS image(s). You can write to it or delete its contents from the router’s console. Usually it comes in sizes of 4MB for the smaller routers (1600 series) and goes up from there depending on the router model.

Configuration Register

Keeping things simple, the Configuration Register determines if the router is going to boot the IOS image from its Flash, tftp server or just load the RXBoot image. This register is a 16 Bit register, in other words has 16 zeros or ones. A sample of it in Hex would be the following: 0×2102 and in binary is : 0010 0001 0000 0010.

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In preparation of our CCNA exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNA exam. So to assist you, below we will discuss Cisco VLAN Trunking Protocol.

VLAN Trunking Protocol (VTP) is a Cisco Layer 2 messaging protocol that manages the addition, deletion, and renaming of VLANs on a network-wide basis. Virtual Local Area Network (VLAN) Trunk Protocol (VTP) reduces administration in a switched network. When you configure a new VLAN on one VTP server, the VLAN is distributed through all switches in the domain. This reduces the need to configure the same VLAN everywhere. VTP is a Cisco-proprietary protocol that is available on most of the Cisco Catalyst Family products.

VTP ensures that all switches in the VTP domain are aware of all VLANs. There are occasions, however, when VTP can create unnecessary traffic. All unknown unicasts and broadcasts in a VLAN are flooded over the entire VLAN. All switches in the network receive all broadcasts, even in situations where few users are connected in that VLAN. VTP pruning is a feature used to eliminate (or prune) this unnecessary traffic.

By default, all Cisco Catalyst switches are configured to be VTP servers. This is suitable for small-scale networks where the size of the VLAN information is small and easily stored in all switches (in NVRAM). In a large network, a judgment call must be made at some point when the NVRAM storage needed is wasted, because it is duplicated on every switch. At this point, the network administrator should choose a few well-equipped switches and keep them as VTP servers. Everything else participating in VTP can be turned into a client. The number of VTP servers should be chosen so as to provide the degree of redundancy desired in the network.

Modes of Operation

Server

In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters (such as VTP version and VTP pruning) for the entire VTP domain. VTP servers advertise their VLAN configuration to other switches in the same VTP domain and synchronize their VLAN configuration with other switches based on advertisements received over trunk links. VTP server is the default mode.

Transparent

VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, transparent switches do forward VTP advertisements that they receive out their trunk ports.

Client

VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.

Advertisements

Summary Advertisements

When the switch receives a summary advertisement packet, it compares the VTP domain name to its own VTP domain name. If the name is different, the switch simply ignores the packet. If the name is the same, the switch then compares the configuration revision to its own revision. If its own configuration revision is higher or equal, the packet is ignored. If it is lower, an advertisement request is sent.

Subset Advertisements

When you add, delete, or change a VLAN in a switch, the server switch where the changes were made increments the configuration revision and issues a summary advertisement, followed by one or several subset advertisements. A subset advertisement contains a list of VLAN information. If there are several VLANS, more than one subset advertisement may be required in order to advertise them all.

Advertisement Requests

A switch needs a VTP advertisement request in the following situations:

The switch has been reset. The VTP domain name has been changed. The switch has received a VTP summary advertisement with a higher configuration revision than its own. Upon receipt of an advertisement request, a VTP device sends a summary advertisement, followed by one or more subset advertisements. Configuration

To configure an IOS based switch to be a VTP server, issue the following commands:

SwitchA# vlan database SwitchA(vlan)# vtp domain vtpdom SwitchA(vlan)# vtp server SwitchA(vlan)# exit

These commands configure the switch to be a VTP server in the VTP domain vtpdom. The changes are saved and the revision number is incremented when the exit command is issued.

To configure a VTP client, run the following commands:

SwitchB# vlan database SwitchB(vlan)# vtp domain vtpdom SwitchB(vlan)# vtp client SwitchB(vlan)# exit

To disable VTP, set the vtp mode to transparent as such:

SwitchC# vlan database SwitchC(vlan)# vtp transparent SwitchC(vlan)# exit

To monitor the VTP operation and status, use either:

SwitchA# show vtp status SwitchA# show vtp counters

I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. I am sure you will quickly find out that hands-on real world experience is the best way to cement the CCNA concepts in your head to help you pass your CCNA exam!

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In preparation of your CCNA exam, we want to make sure we cover the various concepts that we could see on your Cisco CCNA exam. So to assist you, below we will discuss one of the more difficult CCNA concepts; the Three Router Static Route Lab. As you progress through your CCNA exam studies, I am sure with repetition you will find this topic becomes easier. So even though it may be a difficult concept and confusing at first, keep at it as no one said getting your Cisco certification would be easy!

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Objective In this lab, you will configure static routes between all three routers. This will allow your routers to route packets so that all routers and all hosts will be able to reach (ping) each other. Once your configuration is complete, you will use basic techniques to test your network’s connectivity.

Scenario Three separate classful networks need routing between them and their subnets.

Questions: What are the different classful networks? 1. ________________ 2. ________________ 3. ________________ 4. ________________ 5. ________________ Are there any subnets? If so, what are they? 1. _______________ 2. _______________ 3. _______________ 4. _______________ 5. _______________ Setup Configure the cabling as shown in the network diagram If the routers have a startup-config, erase it and perform a reload of the routers. Important! Configure the routers to include hostnames and the proper interface commands including IP addresses, subnet masks, etc. Each router should be able to ping the interface of the adjacent (neighboring) router and the host on its LAN (Ethernet) interface. Test and troubleshoot as necessary. Use the context sensitive help, previous labs, your books and /or handouts and if your still having problems ask your partner or ask the instructor for assistance. Step 1 – Configuring Static Routes On each router configure a separate and specific static route for each network or subnet. You do not need to configure static routes for the router’s directly connected network(s) because like a host, by configuring the IP address and subnet mask on an interface tells the router that it belongs to that network/subnet.

Router1 Router1(config)# ip route 172.16.3.0 255.255.255.0 172.16.2.1 Router1(config)# ip route 192.168.2.0 255.255.255.0 192.168.1.1 Router2 Router2(config)# ip route 172.16.1.0 255.255.255.0 172.16.2.2 Router2(config)# ip route 192.168.1.0 255.255.255.0 172.16.2.2 Router2(config)# ip route 192.168.2.0 255.255.255.0 172.16.2.2 Router3 Router3(config)# ip route 172.16.1.0 255.255.255.0 192.168.1.2 Router3(config)# ip route 172.16.2.0 255.255.255.0 192.168.1.2 Router3(config)# ip route 172.16.3.0 255.255.255.0 192.168.1.2 Verify and Validate: All hosts and all routers should be able to ping every interface in the network. Do a “show running-config” and notice the static routes that you entered. Router# show ip route o What routes to networks do you see? o Which routes are static and which routes are directly connected? o What is the administrative distance for a static route? o What is the administrative distance for a directly connected network? Questions: How does the next-hop-ip-address help with the routing process? _____________________________________________. Does it give the entire route, i.e., subnet mask? _________________ What is it actually doing regarding the routing of the packet? ____________________________________________ How does a packet get from Host 2 to Host 3? ____________________________________________ ____________________________________________ ____________________________________________ Instead of a next-hop-ip-address, what else could you have used? ____________________________________________. What would you need to do if you added new networks or deleted/modified existing networks? ____________________________________________ ____________________________________________ ____________________________________________ Is there any way to summarize several static routes to multiple subnets into a single static route? _____________________________________________ _____________________________________________ _____________________________________________ Outputs Router2#show ip route (Output omitted) Gateway of last resort is not set

172.16.0.0/24 is subnetted, 3 subnets S 172.16.1.0 [1/0] via 172.16.2.2 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, Ethernet0 S 192.168.1.0/24 [1/0] via 172.16.2.2 S 192.168.2.0/24 [1/0] via 172.16.2.2

Router1#show ip route (output omitted) Gateway of last resort is not set

172.16.0.0/24 is subnetted, 3 subnets

C 172.16.1.0 is directly connected, Ethernet0 C 172.16.2.0 is directly connected, Serial0 S 172.16.3.0 [1/0] via 172.16.2.1 C 192.168.1.0/24 is directly connected, Serial1 S 192.168.2.0/24 [1/0] via 192.168.1.1

Router3#show ip route (Output omitted) Gateway of last resort is not set

172.16.0.0/24 is subnetted, 3 subnets S 172.16.1.0 [1/0] via 192.168.1.2 S 172.16.2.0 [1/0] via 192.168.1.2 S 172.16.3.0 [1/0] via 192.168.1.2 C 192.168.1.0/24 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0

Step 2 – Configuring Summary Static Routes The configuration of the routers in Step 1 works just great and is a valid way to configure routing on these networks. Earlier, we noticed that the network 172.16.0.0 is divided into several subnets. The Router3 router does not really need separate static routes for each subnet, since all of the 172.16.0.0 subnets can be reached via the same next-hop-ip-address, i.e. Router1. Let’s reconfigure the static routes on Router3 so that it only uses a single static route to reach all of the 172.16.0.0 subnets.

Router1 No changes Router2 No changes Router3 First, remove the current static routes: Router3(config)# no ip route 172.16.1.0 255.255.255.0 192.168.1.2 Router3(config)# no ip route 172.16.2.0 255.255.255.0 192.168.1.2 Router3(config)# no ip route 172.16.3.0 255.255.255.0 192.168.1.2 Now, add the new summary static route: Router3(config)# ip route 172.16.0.0 255.255.0.0 192.168.1.2 Verify and Validate: All hosts and all routers should be able to ping every interface in the network. Do a “show running-config” and notice the static routes that you entered. Router3# show ip route o What routes to networks do you now see? Questions: What made this new summary static route work for all subnets? _____________________________________________________ _____________________________________________________ _____________________________________________________ Why is a single summary static route an advantage regarding the size of the routing table? _____________________________________________________ _____________________________________________________ _____________________________________________________ Why is a single summary static route an advantage regarding future changes to the 172.16.0.0 network? _____________________________________________________ _____________________________________________________ _____________________________________________________ Outputs Router3#show ip route (Output omitted)

Gateway of last resort is not set S 172.16.0.0/16 [1/0] via 192.168.1.2 C 192.168.1.0/24 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0

Step 3 – Configuring Default Static Routes Both Step 1 and Step 2 are acceptable ways to configure routing for these networks. We notice that the 172.16.3.0/24 and the 192.168.2.0/24 networks are “stub networks,” meaning that there is only one way out (both via Router1).

Router1 No changes Router2 First, remove the current static routes: Router2(config)# no ip route 172.16.1.0 255.255.255.0 172.16.2.2 Router2(config)# no ip route 192.168.1.0 255.255.255.0 172.16.2.2 Router2(config)# no ip route 192.168.2.0 255.255.255.0 172.16.2.2 Now, add the new default static route: Router2(config)# ip route 0.0.0.0 0.0.0.0 172.16.2.2 Router3 First, remove the current static routes: Router3(config)# no ip route 172.16.0.0 255.255.0.0 192.168.1.2 Now, add the new default static route: Router3(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.2 Verify and Validate: All hosts and all routers should be able to ping every interface in the network. Do a “show running-config” and notice the static routes that you entered. Router2# show ip route o What routes to networks do you now see? Router3# show ip route o What routes to networks do you now see? Questions: Do you think static routes are still used even with dynamic routing (RIP, OSPF, etc.)? _______________. Hint: Think about the administrative distance. Do you think default static routes are still used even with dynamic routing (RIP, OSPF, etc.)? _______________. What is the disadvantage of doing this? How would a default static route be properly used in a real world network? (How would a company’s network use a default route when connecting to the Internet?) ________________________________________ ________________________________________ ________________________________________ Outputs Router3#show ip route (Output omitted)

Gateway of last resort is 192.168.1.2 to network 0.0.0.0

C 192.168.1.0/24 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 S* 0.0.0.0/0 [1/0] via 192.168.1.2

Save your current configuration to NVRAM.

End of Lab I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. Achieving your CCNA certification is much more than just memorizing Cisco exam material. It is having the real world knowledge to configure your Cisco equipment and be able to methodically troubleshoot Cisco issues. So I encourage you to continue in your studies for your CCNA exam certification.

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