Free CCNA | OSPF Part 2 | Day 27 | CCNA 200-301 Complete Course

Welcome to Jeremy’s IT Lab

This section introduces the course and covers the basics of OSPF.

Introduction to OSPF

• OSPF is item 3.4 on the official exam topics list.

• OSPF router ID and configuring single area OSPFv2 are covered in part 1.

Topics Covered in this Video

• OSPF's metric, known as cost, which is based on interface bandwidth.

• How routers become OSPF neighbors.

• Additional OSPF configurations.

OSPF Metric: Cost

This section explains how OSPF's metric, called cost, is calculated based on interface bandwidth.

Calculating Cost

• The cost of an interface is determined by dividing the reference bandwidth by the interface's bandwidth.

• The default reference bandwidth for OSPF is 100 megabits per second.

• Examples of calculating costs for different types of interfaces are provided.

Changing Reference Bandwidth

This section explains how to change the reference bandwidth and why it may be necessary.

Modifying Reference Bandwidth

• The reference bandwidth can be changed using the command AUTO-COST REFERENCE-BANDWIDTH <value>.

• It is recommended to configure a reference bandwidth greater than the fastest links in your network for future upgrades.

• Consistency in reference bandwidth across all routers ensures consistent costs for each interface bandwidth.

Total Cost and Routing Table

This section discusses how total cost affects routing decisions and examines R1's routing table.

Total Cost Calculation

• The total cost to reach a destination is the sum of costs of outgoing or exit interfaces.

• Loopback interfaces have a cost of 1.

Conclusion

This transcript provides an overview of OSPF, including its metric (cost) calculation, changing the reference bandwidth, and understanding total cost for routing decisions. The notes are organized in a clear and concise manner, with timestamps provided for easy reference to the corresponding parts of the video.

Understanding OSPF Cost and Interface Configuration

In this section, we learn about OSPF cost and how to configure it on interfaces. We also explore the difference between interface speed and bandwidth.

OSPF Cost Calculation

• The cost of a route in OSPF is calculated based on the reference bandwidth divided by the interface bandwidth.

• The reference bandwidth can be changed using the auto-cost reference-bandwidth command.

• The default reference bandwidth is 100 Mbps.

• Changing the reference bandwidth affects all routers in the OSPF domain.

Manually Configuring OSPF Cost

• The OSPF cost of an interface can be manually configured using the ip ospf cost command followed by the desired cost value.

• This configuration takes priority over auto-calculated costs.

• It is recommended to change the reference bandwidth instead of manually configuring individual interface costs.

Interface Bandwidth vs Speed

• Interface bandwidth is used for calculating OSPF cost, EIGRP metric, etc., but it does not affect the actual speed at which data is transmitted.

• To change the speed at which an interface operates, use the speed command.

Changing Interface Bandwidth

• The interface bandwidth can be changed using the bandwidth command followed by the desired value in kilobits per second (Kbps).

• However, changing interface bandwidth is not recommended as it affects calculations beyond just OSPF cost.

Modifying OSPF Cost: Reference Bandwidth and Interface Configuration

In this section, we explore different methods to modify OSPF costs, including changing reference bandwidth and manually configuring costs on individual interfaces.

Changing Reference Bandwidth

• The reference bandwidth can be modified using the auto-cost reference-bandwidth command followed by a value in megabits per second (Mbps).

• This affects all routers in the OSPF domain and is used in calculating OSPF costs.

Manually Configuring Interface Cost

• The OSPF cost of an interface can be manually configured using the ip ospf cost command followed by the desired cost value.

• This configuration takes priority over auto-calculated costs.

Changing Interface Bandwidth

• The interface bandwidth can be changed using the bandwidth command followed by the desired value in kilobits per second (Kbps).

• However, changing interface bandwidth is not recommended as it affects calculations beyond just OSPF cost.

Checking OSPF Cost and Overview of OSPF Neighbors

In this section, we learn how to check OSPF costs and get an overview of OSPF neighbors.

Checking OSPF Cost

• The command show ip ospf interface brief provides a convenient overview of each OSPF-enabled interface on the router, including their respective costs.

Understanding OSPF Neighbors

• Ensuring successful neighbor formation is crucial for proper functioning of OSPF.

• Routers become neighbors by exchanging hello messages at regular intervals.

• Hello messages are multicast to IP address 224.0.0.5, which is the multicast address for all OSPF routers.

• Neighbor formation goes through various states before becoming established.

Establishing OSPF Neighbors

In this section, we explore how routers become neighbors in OSPF and why it is important for proper operation.

Neighbor Formation Process

• When OSPF is activated on an interface, routers send hello messages at regular intervals to potential neighbors.

• Hello messages are used to check compatibility and negotiate neighbor relationships.

• Default hello timer on Ethernet connections is 10 seconds.

Multicast Address and IP Header

• Hello messages are multicast to IP address 224.0.0.5, the multicast address for all OSPF routers.

• OSPF messages are encapsulated in an IP header with a protocol field value of 89 to indicate OSPF.

Importance of Neighbor Formation

• Successful neighbor formation is essential for sharing network information and calculating routes in OSPF.

• Basic OSPF operation relies on routers becoming neighbors, making it a critical aspect of configuration and troubleshooting.

New Section

This section explains the initial OSPF neighbor states and the process of establishing OSPF adjacency.

OSPF Neighbor States

• In the 'Down' state, R1 sends an OSPF hello message to 224.0.0.5, but it doesn't know about any neighbors yet.

• When R2 receives the Hello packet, it adds an entry for R1 in its OSPF neighbor table, transitioning to the 'Init' state.

• The 'Init' state means that R2 received a Hello packet from R1 but doesn't have its own router ID in it yet.

• In the '2-way' state, both routers exchange Hello packets containing their respective router IDs and become aware of each other as neighbors.

• Once both routers reach the '2-way' state, they are ready to share Link State Advertisements (LSAs) and build a common Link State Database (LSDB).

• If routers fail to reach the '2-way' state, troubleshooting is required to identify and resolve any issues preventing adjacency.

LSDB Exchange Process

• After reaching the '2-way' state, routers determine which one will be the Master and which will be the Slave in the Exstart state based on their router IDs.

• In the Exchange state, routers exchange Database Description (DBD) packets containing basic information about their LSAs without sending them yet.

• The Loading state follows where routers send Link State Request (LSR) messages to request missing LSAs from their neighbors based on exchanged DBDs.

• Once LSR requests are made, routers send Link State Update (LSU) messages to transmit the actual LSAs.

• The Loading state concludes when all routers have the same LSDB and move to the Full state, establishing a full OSPF adjacency.

Maintaining OSPF Adjacency

• In the Full state, routers have identical LSDBs, but they continue sending Hello packets every 10 seconds to maintain neighbor adjacency.

• A 'Dead' timer is used to reset whenever a Hello packet is received; if it reaches zero without receiving a Hello message, the neighbor is removed.

• Routers continuously share LSAs as the network changes to ensure an accurate map of the network. This dynamic routing capability is a key advantage of OSPF.

New Section

This section provides an overview of the different states in OSPF and how routers establish adjacency.

OSPF States

• In the Init state, R2 receives the first Hello packet from R1, but R2's own router ID is not included yet.

• In the 2-way state, routers exchange more hello packets and include their respective router IDs in the hellos.

• The Exstart state involves exchanging DBD packets to determine the Master and Slave routers.

• In the Exchange state, routers exchange DBD packets to share information about their LSDB contents.

• The Loading state uses LSRs (Link State Requests) to request LSAs from each other, which are sent in LSU (Link State Update) packets.

• LSAck packets are sent to acknowledge received LSAs. Once all these steps are completed, routers reach the Full state and have a full OSPF adjacency.

New Section

This section explains the three main steps in sharing LSAs and determining best routes in OSPF.

Sharing LSAs and Determining Best Routes

• The three main steps in sharing LSAs and determining best routes are: becoming neighbors, exchanging LSAs, and calculating the best routes using metrics.

• Becoming neighbors involves the Init, 2-way, and Exstart states where hello packets are exchanged between routers.

• Exchanging LSAs occurs in the Exchange state where DBD packets are shared to synchronize the Link State Database (LSDB).

• Calculating the best routes is done using the metric (cost) assigned to each route.

New Section

This section provides a basic overview of OSPF and presents a summary chart of OSPF message types.

Basic Overview of OSPF

• OSPF is a dynamic routing protocol that uses cost as its metric to determine the best routes.

• There are five different OSPF message types: Hello, DBD, LSR, LSU, and LSAck.

• Each message type serves a specific purpose in establishing and maintaining OSPF adjacency.

New Section

This section explores some OSPF show commands and their output.

OSPF Show Commands

• The show ip ospf neighbor command displays information about OSPF neighbors, including their state and router IDs.

• The show ip ospf interface command provides details about OSPF-enabled interfaces, such as hello timers and neighbor counts.

• The output of these commands can help monitor the status of OSPF neighbors and interfaces.

New Section

This section explains the concept of passive interfaces in OSPF configuration.

Passive Interfaces

• Passive interfaces do not participate in routing updates but still advertise network information to other routers.

• The passive-interface default command makes all interfaces passive by default, while no passive-interface removes this setting for specific interfaces.

• Configuring passive interfaces can help reduce unnecessary traffic on certain links or networks.

New Section

This section discusses OSPF configurations and enabling OSPF on interfaces.

Enabling OSPF on Interfaces

• OSPF can be enabled directly on an interface using the ip ospf <process ID> area <area ID> command.

• This method allows OSPF to be activated without using the network command.

• The show ip protocols command displays information about OSPF configurations, including activated interfaces.

New Section

This section covers additional OSPF configuration options.

Additional OSPF Configurations

• The network command is used to activate a routing protocol on specific interfaces. It is commonly used in RIP, EIGRP, and OSPF configurations.

• The passive-interface default command configures all router interfaces as passive by default, while the no passive-interface command removes this setting for specific interfaces.

• These commands provide flexibility in configuring passive interfaces in OSPF.

New Section

This section reviews the concept of cost (metric) in OSPF and its calculation.

Reviewing Cost Calculation

• Cost (metric) in OSPF is calculated by dividing the reference bandwidth by the actual bandwidth of an interface. If the result is less than 1, it is converted to 1.

• The show ip protocols command displays information about cost calculation and other OSPF parameters.

New Section

This section covers OSPF configurations, neighbor states, and default costs.

OSPF Configurations

• OSPF can be activated on an interface directly using the command ip ospf <process-id> area <area-id> instead of using the NETWORK command.

• Passive interfaces can be configured by using the passive-interface default command to make all interfaces passive, and then activating specific interfaces.

OSPF Neighbor States

• The OSPF neighbor states are as follows: Down, Init, 2-way, Exstart, Exchange, Loading, and Full.

• The Master and Slave roles are decided in the Exstart state.

• In the 2-way state, designated routers and backup designated routers are selected.

• LSRs (Link State Requests), LSUs (Link State Updates), and LSAcks (Link State Acknowledgments) are exchanged in the Loading state.

Default OSPF Cost

• FastEthernet, Gigabit Ethernet, and 10Gig Ethernet interfaces have the same default cost in OSPF.

• The cost is calculated by dividing the reference bandwidth by the interface bandwidth.

• The default reference bandwidth is 100 megabits per second.

Quiz Questions

1. Put the OSPF neighbor states in the correct order: Down, Init, 2-way, Exstart, Exchange,

Loading,and Full.

2. Which statement about OSPF's default cost is correct? c) FastEthernet,

Gigabit Ethernet,and 10Gig Ethernet interfaces have

the same cost.

3. In which OSPF neighbor state are the Master

and Slave roles decided? A) Exstart.

4. Which of these commands can be used to make

a FastEthernet interface have an OSPF cost of 100? C) AUTO-COST REFERENCE-BANDWIDTH 10,000.

5. What are the default OSPF Hello / Dead timers

on an Ethernet connection? B) Hello 10 seconds, Dead 40 seconds.

Bonus Question

• The cost of the route from RouterA to RouterC in the given OSPF network is 3.

Please refer to the transcript for detailed explanations and additional information.

New Section

This section discusses the practice exams recommended by the speaker for CCNA and CCNP exams. Supplementary materials such as flashcards and packet tracer practice labs are also mentioned.

Practice Exams and Supplementary Materials

• The speaker highly recommends using the practice exams provided in the video description for CCNA and CCNP exams. These exams have been personally used by the speaker.

• Supplementary materials, including a flashcard deck for Anki software and a packet tracer practice lab, are available.

• To access the flashcards and packet tracer lab files for the course, viewers can sign up for the speaker's mailing list via the link in the video description.

New Section

In this section, the speaker expresses gratitude towards JCNP-level channel members and mentions that flashcards and packet tracer lab files will be sent to those who sign up for their mailing list.

Gratitude Towards JCNP-Level Channel Members

• The speaker extends thanks to JCNP-level channel members named Marko, Florian, Daming, Venkatesh, Kone, Joshua, Jhilmar, Samil, Ed, Value, Magrathea, Justin, John, funnydart, Scott, Hassan,

Gerrard,Tibi,Joyce,Marek,Velvijaykum,C Mohd,Johan,

Mark,Miguel,Yousif,Sidi,Boson Software,

Charlesetta ,Devin,Lito,Mike,Yonatan,and Vance.

• The speaker acknowledges that one of the channel members is still displaying as "Channel failed to load" and requests them to inform if they encounter any issues so that YouTube can address it.

• This is a list of JCNP-level channel members as of August 11th 2020. Newer members may not be included in this list but will be acknowledged in future videos.

New Section

The speaker concludes the video by encouraging viewers to subscribe, like, comment, and share the video.

Conclusion and Call to Action

• The speaker thanks viewers for watching the video.

• Viewers are encouraged to subscribe to the channel, like the video, leave a comment, and share it with others.