Overview

In the video tutorials below, I show how to use Packet Tracer to build a small LAN with a Cisco 2960 Switch, three PC clients, and two PC servers, one of the servers is placed on a separate VLAN for management purposes. Excellent review and study for the Cisco CCNA exam. The networking tasks that are accomplished in the videos are:{loadposition adposition5}

  • Changing the management VLAN on the switch,
  • Configuring the switch with an IP address,
  • Configuring the switchports as access ports and assigning them to VLANs,
  • Remotely connecting to the switch with telnet,
  • Configuring passwords for console and virtual terminal ports,
  • Configure privileged user mode with an md5 encrypted password,
  • Configuring the hostname on the switch,
  • Testing LAN connections with the Ping utility,
  • Backing up the switch configuration file and IOS image file to a TFTP server using the copy command,
  • Using the show mac-address-table command,
  • Configuring switchport port-security and sticky mac address

Video Tutorials

Overview

Open Shortest Path First (OSPF) is a link-state routing protocol that is designed to work with large, more complex networks. OSPF is a classless routing protocol that supports VLSM and CIDR, and uses the Shortest Path First (SPF) algorithm to calculate the best path to a network. {loadposition adposition5}OSPF uses a routing metric of "cost" that in Cisco's implementation is based mainly on the bandwidth of a link. OSPF is able to support hierarchical and scalable network designs through its ability to handle multiple OSPF routing areas.

The Cisco CCNA curriculum requires students to know how to implement and configure only a single-area OSPF network.

OSPF has some similarities to EIGRP, especially in regards to configuration, like requiring a process-id number, using wildcard bits for the subnet mask, hello packets, neighbor relationships or adjacencies, triggered updates, and the use of multiple tables like the neighbor and topology tables.

Characteristics

• Algorithm - Dijsktra's SPF algorithm
• Metric - Cost, which is based on the bandwidth of a link 
• Administrative Distance - 110
• Process-ID number - the process-id number is declared when OSPF is started/configured and is a number from 1 to 65535. The process id number does NOT need to match other OSPF routers in the area in order to create adjacencies (see commands below).
• Wildcard bits/mask - The wildcard mask is the inverse of a network subnet mask (e.g. 255.255.255.0 is 0.0.0.255). It is declared after the network number in the network command (see commands below)
• Area number - The area number is a number from 0-255, declared at the end of the network command after the wildcard bits. Routers in the same area will exchange routing information or Link State Updates or LSUs (see commands below)
• Hello Interval - Hello packets are sent every 10 seconds by default. In order for OSPF routers to establish neighbor adjacencies and exchange routing information successfully, the hello interval needs to match all OSPF routers in the OSPF area. 
• Dead Interval - The dead interval is 40 seconds by default. The dead interval should be 4 times the hello interval, and needs to match all OSPF routers in the area
• Multiple Tables - Routing Table, Topology Table, and Neighbor Adjacency Table
• DR and BDR Elections - In broadcast multi-access networks (Ethernet), routers in the OSPF area will elect a Designated Router (DR) and a Backup Designated Router (BDR). The DR will be the receiver and distributor of Link-State Packets to other routers in the OSPF area. The BDR will wait, and be ready to take over the duties of the DR in case it fails.

IOS CLI Commands

The router ospf command starts the OSPF routing process. The process ID number can be a number between 1 and 65535:

 router(config)# router ospf <process-id>

  EXAMPLE: router(config)# router ospf 1

The network command will add a connected network to the routing process. In addition to the network IP address you need to provide the wildcard mask, which is the inverse of the subnet mask and the area parameter and number. Typically in single area OSPF the area is often set to area 0.

 router(config-router)# network <network-number> <wildcard-mask> area <area-number>

  EXAMPLE: router(config-router)# network 192.168.1.0 0.0.0.255 area 0
  EXAMPLE: router(config-router)# network 172.16.0.0 0.0.255.255 area 0
  EXAMPLE: router(config-router)# network 201.132.33.4 0.0.0.3 area 0 //for a /30 subnet mask

In OSPF, the router-id command will manually set the router's router-id. In broadcast multi-access networks the router with the highest router-ID will become the designated router (DR) and the router with the second highest router-ID will become the backup designated router (BDR).

 router(config-router)# router-id <ip-address>

  EXAMPLE: router(config-router)# router-id 192.168.100.254

The passive-interface command can be used to stop OSPF packets from being sent out of a network interface where there are no other OSPF routers present.

 router(config-router)# passive-interface <interface-number>

  EXAMPLE: router(config-router)# passive-interface fastEthernet 0/0

Cisco's OSPF cost metrics do not account for links faster than 100 Mbps. For example, a 100 Mbps Ethernet interface will calculate to an OSPF cost of 1, but what if you have a 1000 or 10000 Mbps Ethernet interface? The auto-cost reference-bandwidth can adjust the cost metrics to account for links fast than 100 Mbps.

 router(config-router)# auto-cost reference-bandwidth <megabits-per-second>

  EXAMPLE: router(config-router)# auto-cost reference-bandwidth 10000

The default-information originate command will distribute a default route to other OSPF area routers.

 router(config-router)# default-information originate 

You can use either of the following commands to exit out of router configuration mode.

 router(config-router)# end
 router(config-router)# exit

Since OSPF relies on bandwidth for the metric, it is a good idea to set the specific bandwidth of the serial interface, otherwise the Cisco serial interfaces will default to a speed of 1544 Kbps, which may lead to an inaccurate measurement of the cost of the link. It is important to remember that this command is applied to the network interface in interface configuration mode.

 router(config)# interface serial <interface-number>
 router(config-if)# bandwidth <speed-in-kbps>

  EXAMPLE: router(config)# interface serial 0/0/0
           router(config-if)# bandwidth 384

Another command that is applied to a network interface is the ip ospf priority command. This command can be used to manipulate the DR/BDR election process. By default, the Cisco router's interfaces are all given an OSPF priority of 1, by changing this value to a higher number you can effect the DR/BDR elections. An OSPF priority of 0 will insure the router is never the DR, but an OSPF priority number of 255 will insure that the router will be elected as the designated router or DR.

 router(config-if)# ip ospf priority <0-255>

  EXAMPLE: router(config-if)# ip ospf priority 255

The following commands are all applied to a network interface, but they all effect the OSPF routing protocol operation. Instead of configuring the bandwidth of the link, which will subsequently effect the calculation of the cost metric, you can configure the cost value directly. To do this you need to know how to manually calculate the cost metric. The cost metric of a network link is calculated by the following method: cost equals 10^8 power divided by the network interface speed in bits per second, e.g. the cost for Fast Ethernet is 10^8/100,000,000 = 1..

 router(config-if)# ip ospf cost <cost-value>

  EXAMPLE: router(config-if)# ip ospf cost 781 //for a 128kbps link

For neighboring OSPF routers to achieve adjacencies the OSPF hello interval and dead interval, on each OSPF router needs to match. In a multi-access, broadcast network the default hello interval is 10 seconds, and the dead interval is set to four times the hello interval, or 40 seconds. You can manipulate these times to, for example: have less hello packets on the network, but if you adjust the hello interval, you also need to adjust the dead interval, and you need to do so, for all OSPF routers in the OSPF area.   

 router(config-if)# ip ospf hello-interval <seconds>
 router(config-if)# ip ospf dead-interval <seconds>

  EXAMPLE: router(config-if)# ip ospf hello-interval 10
           router(config-if)# ip ospf dead-interval 40

The following show commands are useful in verifying and troubleshooting OSPF operation and configuration, as well as identifying the router-ids and the identities of the DR and BDR. 

 router# show ip ospf neighbor
 router# show ip ospf interface
 router# clear ip ospf process
 router# show running-config
 router# show ip protocols
 router# show ip route

Sample command usage:

router(config)#router ospf 1
router(config-router)#network 192.168.0.0 0.0.0.255 area 0
router(config-router)#network 192.168.50.0 0.0.0.255 area 0
router(config-router)#passive-interface fa0/1
router(config-router)#default-information originate
router(config-router)#end
router#show ip ospf neighbor
router# show ip ospf interface
router# clear ip ospf process

Analyzing Show Commands

Example OSPF Network

     router#show ip ospf neighbor

In the "show ip ospf neighbor" command above you can see that the router R0 has established three neighbor relationships or adjacencies with the other routers. The "Neighbor ID" above is the neighbor router's Router ID#. The Router ID# can be different than the neighbor router's IP address on the network. In the example above the first router listed has a Router or Neighbor ID of 200.10.10.253 but its IP address on the network is 192.168.50.1. You can also see that router at 192.168.50.3 (R3) is the current BDR or Backup Designated router and that the "Pri" or Router Priority Number has been changed from the default number of 1 to 50. The "State" shows that all three routers have current "FULL" adjacency or neighbor relationships. DROTHER routers will only form FULL adjacencies with DR and BDR routers and 2WAY adjacencies with each other. You can see this in the image of R1's "show ip ospf neighbor" output above. Even if we only look at the output of R0's show command above (top router output image) we can infer that the Designated Router or DR must be the router that issued the command (R0), because of the fact that there is no neighbor listed as a DR, only a BDR and two DROTHERs.  

     router#show ip route

In the image above, the "show ip route" command has been issued, displaying router R0's routing table. From the routing table we can tell that the R0 router has two connected networks "c 192.168.0.0 on FastEthernet0/1" and "c 192.168.50.0 on FastEthernet0/0" and that it has learned from OSPF about routes to three additional "o" networks: 192.168.1.0, 192.168.3.0, and a "o*E2" 0.0.0.0 candidate default route/gateway of last resort. 

Link-State Routing Protocols Overview

Link-State Routing protocols are routing protocols whose algorithms calculate the best paths to networks differently than Distance Vector routing protocols. Whereas Distance Vector protocols know routes by measures of distance and vector(direction) as reported by neighboring routers, Link-State routing protocols calculate their network routes by building a complete topology of the entire network area and then calculating the best path from this topology or map of all the interconnected networks.

{loadposition adposition5}There are two link-state routing protocols, OSPF and IS-IS. The Cisco CCNA curriculum covers the Open Shortest Path First or OSPF link-state routing protocol, and the IS-IS routing protocol is part of the CCNP curriculum.

Link-State Characteristics

• SPF algorithm - Link-State routing protocols are designed around Dijkstra's Shortest Path First Algorithm (SPF) in which the shortest path from point A to point B is build around a metric of cost.
• Cost metric - SPF algorithm finds the shortest path based on a metric network link costs. Each router measures the cost of its own directly connected networks or "links." Cost is a measure of the quality of a link based mostly on bandwidth.
• Hello packets - Link-State routing protocols establish adjacencies with neighboring routers using hello packets.
• Link State Packets (LSP) - Initial flooding of link-states to all routers in the network.
• Topology or SPF Tree - Link-State routing protocols build and maintain a complete map or topology of the network area.  

Link-State Advantages

• Faster Convergence - Unlike Distance Vector routing protocols which run algorithm calculations before sending updates, Link-State routing protocols send link-state updates to all routers in the network before running route calculations
• Triggered Updates - Unlike Distance Vector routing protocols (except EIGRP) which send periodic updates at regular intervals, Link-State routing protocols send LSPs during router startup (flooding) and when a link changes states like going up or down. If their are no changes in the network the protocol only sends hello packets to maintain adjacencies.
• Scalability - Link-State routing protocols support the ability to configure multiple routing "areas" which allows an administrator to segment a routing protocol processes to defined areas which supports the expansion and troubleshooting of much larger networks.
  

Link-State Disadvantages

• Greater Processing Requirements - Link-State routing protocols typically demand greater processing power and memory resources from the router.
• Greater Administrator Knowledge - Link-State routing protocols can demand advanced administrator knowledge to configure and troubleshoot the network area

Overview

Enhanced Interior Gateway Routing Protocol or EIGRP is Cisco's proprietary Distance Vector routing protocol that replaced the earlier IGRP routing protocol. EIGRP introduced significant improvements to the IGRP routing protocol including support for VLSM and CIDR, guaranteed "loop free" routes, and faster convergence times. {loadposition adposition5}

Improvements

• VLSM & CIDR - EIGRP has support for variable length subnet masks (VLSM) and classless inter domain routing (CIDR).
• DUAL algorithm - The diffusing update algorithm or DUAL, provides guaranteed and optimized loop free routes.
• Successor & Feasible Successor routes - The successor route is the best route to a destination network. If available, DUAL and the EIGRP topology database will also calculate a guaranteed loop free backup route called the Feasible Successor route.
• Partial & Bounded Updates - for faster convergence times. No periodic updates like RIP. EIGRP only sends information when there is a change in the network, like a network link going down. EIGRP does not send the entire routing table, just the information that has changed and only to those routers that need the new information.
  
• Routing Metrics - EIGRP uses a 32 bit routing metric that is backwards compatible with IGRP's 24 bit metric. EIGRP's routing metric is not based on hop count like RIP, it is based instead on: Bandwidth, Load, Delay and Reliability, with Bandwidth and then Delay being the most important factors. EIGRP also features MTU and Hop Count as metric vectors, though they are not used in route calculations.
  
• RTP reliable transport protocol - EIGRP uses its own layer 3, layer 4 protocol to exchange routing updates, and information
  
• PDMs protocol dependent modules - can be added to EIGRP so that it can route other routed protocols like Apple Talk and IPX/SPX
  
• Unequal Cost Load Balancing - EIGRP is capable of being configured for unequal cost load balancing
  

Multiple Tables

• Routing Table - the best "loop free" network routes are placed in the routing table
  
• Neighbor Table - neighbor adjacencies are maintained in this table
  
• Topology Table - maintains "loop free" backup routes known as successor routes and feasible successor routes

IOS CLI Commands

The command to start the EIGRP routing process is router eigrp followed by the autonomous system number. The autonomous system number or (AS#) functions more as a process ID number. The AS number needs to be the same on all neighbor EIGRP routers.     

  router(config)# router eigrp <AS/ID-number>

  EXAMPLE: router(config)# router eigrp 1

The command to add a network and interface to the EIGRP routing process is: network <network number> <wildcard mask>. The network number is the network ip address and the wildcard bits is the inverse of the subnet mask in decimal, so a /24 subnet mask or 255.255.255.0 in wildcard bits is 0.0.0.255 and a /16 or 255.255.0.0 would be 0.0.255.255.

 router(config-router)# network <network-number> <wildcard-mask>

  EXAMPLE: router(config-router)# network 192.168.1.0 0.0.0.255
           router(config-router)# network 172.16.0.0 0.0.255.255

If the EIGRP router is a boundary router it will auto-summarize routes by default. A boundary router is a router with multiple interfaces having different classful network ranges and/or different subnet mask lengths. This can cause problems by working against EIGRPs ability to handle VLSM, CIDR, and general routing to non-contiguous networks. The command to turn off auto summarization is no auto-summary.

 router(config-router)# no auto-summary

The redistribute static command will propagate all static routes including the default route to all other EIGRP routers in the network. 

 router(config-router)# redistribute static

The passive-interface command can be used to stop EIGRP packets from being sent out of a network interface where there are no other EIGRP routers present.

 router(config-router)#passive-interface <interface>

 EXAMPLE: router(config-router)#passive-interface fastEthernet 0/0

The no auto-summary command is very useful to taking advantage of EIGRP's ability to route to variable length and discontiguous subnets, however you may want to still use summary addresses in order to optimize your router's routing tables. In this situation you can manually configure and advertise an EIGRP summary address with the ip summary-address command configured on a network interface.

 router(config)# interface <int-type> <int-num>
 router(config-if)# ip summary-address eigrp <as-number> <ip-summary-address> <subnet-mask> <administrative-distance>

  EXAMPLE: router(config)# interface s0/0/0
           router(config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0 5

The following commands will exit from router configuration mode

 router(config-router)# exit
 router(config-router)# end

The following show commands are useful in verifying and troubleshooting EIGRP operation and configuration, as well as identifying the successor and feasible successor routes

 router# show ip eigrp neighbor
 router# show ip eigrp topology
 router# show running-config
 router# show ip protocols
 router# show ip route

Video Tutorials

Overview

The ability of routing protocols to route to networks with Variable Length Subnet Masks (VLSM) and Classless Interdomain Routing (CIDR), along with the creation of NAT and private addressing, has enabled IPv4 to remain a viable network address solution well beyond its original design limitations. 

{loadposition adposition5}When IPv4 addressing was first developed it was designed as a class based system with Class A, B, C, D, E addresses.

If every computer on the internet needed a public IP address we would have run out of IPv4 addresses a long time ago. The development of VLSM and CIDR, NAT, and Private Addressing helped the conservation of IPv4 addresses that was brought about by the need to deal with the exponential growth of the internet and the realisation that IPv4 was simply running out of address space. Since then, IPv4 address space has indeed run out, and IPv6 has been developed which will never run out, but VLSM, CIDR, NAT, and private addressing enabled IPv4 to last much longer than expected and because of those developments IPv4 is still very much in use today.

VLSM - Variable Length Subnet Masks and CIDR - Classless Interdomain Routing

So how does VLSM and CIDR work? CIDR basically means that when routing you are not limited to networks based on /8, /16, or /24 subnet masks, and VLSM means that as long as the address spaces do not overlap, you can divide a classful network like 192.168.1.0 /24 into networks of different sizes and subnet masks like this:

How I divide the networks above into variable sizes is based on the subnet mask and the binary place value of the last "1" bit. I like to call this method the "Magic Number." Notice that the networks above are the same size as the Magic Number of the subnet mask.

the magic number is bold

With CIDR and classless addressing, not only can you divide subnets into smaller subnets you can also generalize or summarize subnets into supernets. A supernet allows a router to put one summary route in its routing table instead of many routes. Take the following example:

Let's say you have a router that is connected to another router that has the following connected networks:

192.168.0.0 /24
192.168.1.0 /24
192.168.2.0 /24
192.168.3.0 /24
192.168.4.0 /24
..to..
192.168.15.0 /24

Instead of configuring 16 static routes to reach all of those networks you could configure one supernet route of 192.168.0.0 /16 thus basically saying, all of the 192.168 networks are over there! Of course, if in fact it is only networks 192.168.0 through 192.168.15 then a more correct supernet route would be 192.168.0.0 /20 which says: networks 192.168.0.0 through 192.168.15.0 are over there, because the /20 subnet mask has a magic number of 16, and networks 192.168.16 and up, are not in the range being summarized.

Video Tutorials on VLSM and CIDR

Video Tutorials - A Packet Tracer walkthrough of VLSM CIDR and Summary Routes

Overview

RIP or the Routing Information Protocol was standardized in RFC1058 in 1988. It was developed from earlier routing protocols developed at Xerox. RIP has three major versions RIPv1 (1988), RIPv2 (RFC2453 1998), and RIPng (RFC2080 1997). RIP version 2 added support for VLSM and CIDR and version ng or next generation adds support for IPv6. 

{loadposition adposition5}RIPv1 Characteristics

1. Classful routing - RIP is a classful routing protocol, it does not send or receive subnet masks, it assumes classful subnet masks

2. Periodic updates - RIP broadcasts routing updates every 30 seconds. It broadcasts the entire routing table in the update.

3. Triggered updates - RIP also broadcasts updates when there is a change in the topology, like a network going up or down.

4. Metric - RIP's metric is hop count. A hop is a router, so a RIP route with metric of 2 means the network is two routers away. RIP's maximum distance is 15 hops. 16 hops is infinity and is used to mark a route as dead. A router that receives a packet  then removed from the routing table. 

5. Administrative Distance - RIP's administrative distance is 120. AD ranks the trustworthiness, or reliability of the route, the lower the administrative distance the better the route.

6. Hold Down Timer - RIP uses a hold down timer of 180 seconds so that it does not propagate bad routes and does not have a count-to-infinity routing loop. Route is flushed at 240 seconds

7. Load Balancing - Default load balancing across 4 equal cost routes. Can go up to 6 routes.

8. Count to infinity - is prevented by hold down timers and by RIPs maximum metric of 15 hops.

9. Routing Loops - are prevented by: Hold Down Timer, Split Horizon Rule, Route Poisoning, Route Poisoning with Poison Reverse, as well as TTL.

10. Automatic Route Summarization. RIP automatically summarizes routes into classful network ranges because it will not allow non-classful network configuration or the propagation of non-classful subnet masks. It can only advertise classful networks. This can cause problems if subnetted networks are configured on multiple router interfaces in a discontiguous manner (see the video tutorials below for a demonstration).

11. Transport Layer - RIP sends out updates on UDP port 520 

IOS CLI commands to use with RIP

router(config)#router rip //to activate RIP
router(config-router)#network <network ip address> //to add a participating network and interface
router(config-router)#passive-interface <interface type> <interface number> //to stop RIP from sending updates out of an interface
router#show running-config //to verify your configuration
router#show ip route //to verify your routing table
router#show ip protocols //to verify your RIP configuration
router#copy running-config startup-config //to save your configuration

Video Tutorials

In this part, I prepare the network and configure the network interfaces

In this part, I demonstrate how RIP auto-summarizes classless subnets

In this part, I demonstrate how auto-summary can create a problem if the networks are discontiguous

Overview

Routing Loops are a risk in networks that utilize an older dynamic routing protocol like RIP. A routing loop is a scenario where data, instead of being routed to its correct destination, is sent from router to router endlessly. This scenario can be caused by routers not receiving updated routing information quickly enough, and as a result, forwarding packets incorrectly and propagating routing information to neighbor routers incorrectly. {loadposition adposition5}When every router in the system has the correct routing information the network is said to be converged. Therefore, it is desirable to use a routing protocol that can converge a network quickly and prevent routing loops. 

Typically distance vector routing protocols like RIPv1, RIPv2 and IGRP, do not converge networks as quickly as link state routing protocols like OSPF and ISIS, with the EIGRP routing protocol being the exception.

Count-to-inifinity is a RIP routing loop scenario whereby the routes in the routing tables keep increasing their hop-count metric. This is caused by incorrect routing information being propagated on the network.

Distance Vector routing protocols have been designed and improved over the years to minimize the possibility of routing loops. RIP uses the following methods and rules to avoid routing loops and count-to-infinity: split horizon, hold down timers, route poisoning, poison reverse, and TTL values.     

Video Tutorial

{loadposition adposition4}

Overview

With complex networks, hierarchically designed networks, networks with redundancy, or networks requiring more than two routers it is often beneficial to use a dynamic routing protocol instead of using only static routes.

Video Tutorials

Distance Vector versus Link State

Various routing protocols and their characteristics

CDP - Cisco Discovery Protocol

Overview

It is important to know how to configure static routes on a router. Many networks are small enough that all of the routing can be handled by a few static routes and a default route out of the network. {loadposition adposition5}If you want to know a router's routes you need to look at its routing table. The routing table will show you connected routes, static routes, if there is a default route, and it will also show you if there are any dynamically learned routes too. In this section we will look at connected routes, static routes and default routes.

Connected Routes

Connected routes are routes to networks directly connected to the router. To establish connected routes all you have to do is bring up your router's interfaces. This means configuring the router's interfaces with IP addresses and subnet masks and making sure they are not in an administratively shutdown state.

To configure a Fast Ethernet interface from global configuration mode:

R1(config)#interface fastethernet 0/0
R1(config-if)#ip address <your ip address> <your subnet mask>
R1(config-if)#description <your description>
R1(config-if)#no shutdown

To configure a serial interface from global configuration mode. You can first check to see if your interface is the DCE and will need a clock rate:

R1#show controllers serial 0/0

Checking the "show controllers" command results to see If the interface is the DCE, you can see from the output below, that the interface is in fact the DCE, and that the clock rate needs to be set.

R1(config)#interface serial 0/0
R1(config-if)#ip address <your ip address> <your subnet mask>
R1(config-if)#clock rate 64000 (only if the interface is the DCE)
R1(config-if)#description <your description>
R1(config-if)#no shutdown

Now that the interfaces have been brought up you can see the connected routes by looking at the routing table by issuing a "show ip route" command and looking for the lines that start with "c":

Static Routes

In the picture below, R1 has three connected networks in its routing table but it does not know about the 192.168.2.0 network and therefore cannot route traffic to it. To solve that problem a static route to the 192.168.2.0 network can be configured. 

both types of static route commands are listed below:

Video Tutorials on Static Routing

Default Routes

In the diagram below R1 needs a default route or gateway of last resort configured so that it can route traffic to unknown networks across the internet. If R1 does not have a default route, traffic to all unknown networks will be dropped, and surfing the Web will not be possible. To configure a default route you must configure a static route to the 0.0.0.0 network and 0.0.0.0 subnet mask to the next hop router or exit interface which has a path out of the network (see below). The commands to create a default route or gateway of last resort are:

     R1(config)#ip route 0.0.0.0 0.0.0.0 <next hop router IP address>
     or
     R1(config)#ip route 0.0.0.0 0.0.0.0 <exit interface>

Once you have configured a default route it will show up in the routing table as an "s" with an asterisk "*" next to it signifying it as a default route. You can also see from the highlighted areas in the routing table output below that the default route is also acknowledged as the "Gateway of last resort is 0.0.0.0 to network 0.0.0.0" (see below):  

Video Tutorial on Default Routes

In this video I demonstrate configuring a default route using Packet Tracer

Subnetting Skills Challenge

Look at the network diagram below, fill in the correct IP addresses based on the information given in the diagram, and click the "Check Your Answer" button to check your answer. Fill in the fields with IP addresses and no subnet masks, the correct subnet masks are assumed.

Note: The diagram above relates to a PT Skills Challenge in the Cisco Routing Protocols and Concepts Curriculum (section 1.5.3 - 2) This visual diagram may help you make sense of that particular Packet Tracer as well as practice your subnetting skills.

Overview

Some of the ideas that are covered in this section are how Cisco routers are put together, their different types of memory, their various interfaces both LAN and WAN, and their start-up processes? Allso in this section there is a review on how to configure a router, how to bring up its interfaces, and how to issue show commands to read its status. This first part of CCNA 2 also covers in an introductory way the router's routing table, and static versus dynamic routing.

{loadposition adposition5}Router Memory

Similar yet different from a regular computer, the router has different kinds of memory ROM, Flash, NVRAM, and SDRAM which all have different functions:

• ROM - POST, Bootstrap, and ROMMON
• Flash - IOS 
• NVRAM - Configuration File
• SDRAM - Running-Config, Routing Table, IOS (everything is loaded and executed from RAM)
  

Notice: The router is a computer but it does not have a traditional hard drive to store files and the operating system, this is accomplished in Flash memory and NVRAM memory.

Router Bootup Process

1. POST - ROM memory,
   
2. Bootstrap - ROM memory,
   
3. Load the IOS - the router has an ordered routine for loading the IOS
   
   1. Flash Memory - the IOS is typically loaded from Flash memory
      
   2. TFTP - if there is no IOS in Flash, the router will search for a network TFTP server,
   3. ROM - if there is no IOS found, the router defaults to a recovery IOS called Rommon,
4. Load the Startup-Config - the router has an ordered routine for loading the startup-config file
   
   1. NVRAM memory - the startup-config file is typically loaded from NVRAM memory
   2. TFTP - if there is no config file in NVRAM, the router will search for a network TFTP server,
   3. Setup-Mode - if there is no configuration file found, the router defaults to setup-mode

The Router's Purpose

The router's purpose or function is to find the best path (route) and switch out of the correct interface. The router will make the decision of the "best path" by first determining the destination network, and second by consulting its routing table.

Static Routing and Dynamic Routing

Routers can be configured to route traffic based on static routes that have to be manually entered by an administrator or by dynamic routes that are created dynamically by a routing protocol. Static routing is a good choice for networks that: never change, are small in size or have only one router, or have only one way out of the network. Dynamic routing is a good choice if a network has multiple routers, is part of a larger network, or if the network changes frequently. For instance, in a situation where the network changes, with a dynamic routing protocol if a network goes down, the routers will inform each other automatically through the routing protocol, and the route will be removed from the routing table; with static routing, if a network goes down, an administrator will have to go in and remove the the static route manually. 

There is a difference between routed or routable protocols and routing protocols. A routed protocol is a protocol that is routable over multiple networks like the internet. Today the de facto routed protocol is TCP/IP. A routing protocol is a protocol used by routers to share information with each other, specifically information about available routes. Examples of routing protocols would be RIP, EIGRP, OSPF, and ISIS.

For the Cisco CCNA certification exam you will need to know how to configure an interior gateway routing protocol in a multiple router network. You will be required to know the following interior gateway routing protocols: RIPv1, RIPv2, EIGRP, and OSPF.   

Routed Protocols
TCP/IP
IPX/SPX (Novell - no longer in use)
Apple Talk (Apple - no longer in use)

The Routing Table and RIP

A demonstration of reading routing tables and activating the RIP routing protocol 

Video Tutorials on Subnetting

The following ten video tutorials represent my most recent series on Cisco CCNA IPv4 subnetting. My personal feeling is that the only way to learn subnetting is to understand how it is working in binary. {loadposition adposition5}Subnetting makes sense if you try to understand it from the perspective of the binary number system. You can definitely tell how important I feel this topic is in order to do well, and pass your Cisco CCNA exam. Out of this series of videos, the last three seem to be the most popular. I hope these videos help your learning on the topic of subnetting.

In the videos I cover classful and non-classful network masks, the binary process of ANDing, class A, class B, and Class C subnetting, and typical IPv4 subnetting questions you may see on a multiple choice exam.

The Format of an IPv4 Address

An IPv4 address can be written in two ways:

   dotted decimal notation - 192.168.1.1
   32-bit binary notation - 11000000.10101000.00000001.00000001

{loadposition adposition5}The address has 4 octets separated by periods and counted from let to right. There are three types of IPv4 addresses: a network address, a host address, and a broadcast address. In other words you could say a computer is on the 192.168.10.0 /24 network (network address), and is using a host address of 192.168.10.1. The address 192.168.10.1 represents the ip address in dotted decimal notation. That same address in binary notation is 11000000.10101000.00001010.00000001. The 1(00000001) is in the 4th octet.

Converting Binary to Decimal and Vice Versa

Network Portion and the Host Portion of an IP Address and Subnet Mask

The network portion and the host portion of an ip address is defined its subnet mask. This process is easy if the subnet mask is classful meaning either:

Class C  -  255.255.255.0  or /24,
Class B  -  255.255.0.0  or /16,
Class A  -  255.0.0.0  or /8

So if the ip address is 192.168.1.100 and the subnet mask is classful meaning 255.255.255.0 then the 255s in the subnet mask tell you the network portion and the 0s tell you the host portion. For example, below the network portion is in red and the host portion is in black:

192.168.1.100
255.255.255.0
(So the network is 192.168.1.0, and the host is number 100)

Using the example above the first address in the network is the network address (192.168.1.0). The last address in the network is the broadcast address (192.168.1.255), and the host addresses in the network are the addresses between the network and the broadcast  (192.168.1.1 - 192.168.1.254).

The process is a little more difficult when a non-classful subnet mask is used. In this scenario binary conversion must be used to delineate the network and host portions of an address. Consider the following example:

192.168.1.100 /27 or

192.168.1.100
255.255.255.224
Where are the network and host portions now?

To easily solve the question convert to binary:
11000000.10101000.00000001.01100100  = 192.168.1.100
11111111.11111111.11111111.11100000 = 255.255.255.224
(The 1s in the subnet mask identify the network portion, the 0s the host portion)

The network and host portions are still defined by the subnet mask, just more accurately by seeing the address and mask in binary and identifying the 1s and 0s. The question that you now have to ask yourself is, what is the networkaddress, broadcast address and host addresses if the subnet mask is 255.255.255.224? To answer this question you need to, in binary, logically AND the ip address and subnet mask and you will get the network address. To understand this process and more see my video series on subnetting, ANDing and the Magic Number below.

Note: you have to have all subnet mask fields filled in.

Application Layer Overview

The Application Layer is the layer closest to the end user. When you are using a program that is going to send something or contact someone over the internet you are using a network application that operates at the Application Layer. Each program/application that sends data over a network is identified by a particular protocol, at Layer 4 this protocol is associated with a port number. For example a web browser like Internet Explorer requests and receives pages from web servers its protocol is HTTP the hyper text transfer protocol and its correlative port number is port 80.

{loadposition adposition5}The applications that we use at Layer 7, the Application Layer are web browsers (HTTP) like Internet Explorer, a file transfer programs (FTP) like Filezilla, email clients (SMTP) like Microsoft Outlook Express and all flavors of Instant Messaging programs and P2P applications. There are also processes that run in the background that run at Layer 7, like DHCP which automates the process of requesting and receiving an IP address from a DHCP server. If you want to see these protocols in action all you need to do is use Wireshark. For instance, if we use the example of DHCP we learn that initiating DHCP involves a DHCP client talking to a DHCP server. The process is: 1. Client sends a DHCP DISCOVER 2. Server responds with a DHCP OFFER 3. Client sends a DHCP REQUEST 4. Server responds with a DHCP ACKnowledgement You can see the process of a client obtaining an IP address with DHCP in Wireshark (see video tutorial below).

This is a diagram of the OSI and TCP/IP Models and how they correspond to PDUs, Protocols and Devices 

Video Tutorials - Wireshark, nslookup, Telnet

In this video I show the process of DHCP address acquisition by analyzing the PDUs using Wireshark

Announcements!

• The Lab is Open & Thursday Night Linux - Is still on! - Despite the fact that I am out sick. Steve and I stayed late in the lab last night preparing for tonight, so tonight's Lab will continue thanks to Steve. Also an announcement was sent out that tonight will be a pot luck, so bring food if you can. Anyone who shows up tonight online or in the lab will get extra credit. Tell Steve to keep a role sheet!

• CCNA Security - Monday & Wednesday we will be working on Chapter 7.

{loadposition adposition5}• Thursday Night, "Linux Night" - Last Thursday was marred by a series of technical difficulties. So this Thursday we will try again! 

• This Tuesday 4/8 - Windows Server Classes Extra Credit! Collaborate Online Conference 6:10pm to 7:00pm. If you are in any of the Windows Server classes make sure to attend! Login to Blackboard, go to the Collaborate area and then launch the All Classes Collaborate session.

• Collaborate/Blackboard - Below is my current online conferencing schedule using Collaborate/Blackboard. Students can join in and ask questions, see and hear answers, and get general help with their class in real-time.

Announcements!

• Last Day of school and to turn in assignments is May 9th!!!!

• Thursday Night, "Linux Night" - Many thanks to Steve for leading everyone in a great new lab last night. Everything was recorded in Collaborate if you missed it. Showing up and doing the lab was worth 5 points extra credit. You can still do it by watching the recording and doing it on your own.

• CCNA Security - Monday & Wednesday we will be working on Chapter 8.

{loadposition adposition5}• Thursday Night, "Linux Night" - Many thanks to Steve for leading last Thursday's Linux session.

• This Tuesday 4/16 - Windows Server Classes Extra Credit! Collaborate Online Conference 6:10pm to 7:00pm. If you are in any of the Windows Server classes make sure to attend! Login to Blackboard, go to the Collaborate area and then launch the All Classes Collaborate session.

• Collaborate/Blackboard - Below is my current online conferencing schedule using Collaborate/Blackboard. Students can join in and ask questions, see and hear answers, and get general help with their class in real-time.

Announcements!

• Linux Tomorrow Night - We will do FreeIPA tomorrow night. It will be an extra credit assignment so make sure you show up online or in person.
  
• Do your student evaluations! - There should be student evaluations available for all of my classes through Blackboard. Please take a second and fill them out.
  
• Grades - I will start grading and adding up points for all of the projects you turned in starting this week. If you need to turn something in late please do so. I will add grades up until the last minute, before I have to submit final grades in Web Advisor.
• Last Day of Class - The last day of class is Finals week May 9th.
  

Announcements!

• Important! Online Student Evaluations - If you are an online student or an SDL student please do an online evaluation. Just log in to Blackboard and do your student class evaluations
• One more week! - Next week is finals week, so get your missing projects and assignments turned in now.
• Thursday night Linux - Last meeting is this Thursday, so lets make it a potluck and bring food! We will do a final project ... probably Cactii

Announcements!

• Last Chance to turn in all unfinished projects and assignments is this Week!!! Get it in.
  
• Students, I will be in the lab grading this week. If you need access to the computers, or some help with finishing anything please stop by.
• I will be busy posting grades until Tuesday the 14th at 5pm.
• Cisco CCNA4 and CCNA Security will be meeting at the regular hours.
• No Thursday Night Linux Lab. Many thanks to Steven B for all his help!