CCNA3 Module 1: Single Area OSPFv2 Concepts - Enterprise Networking Security and Automation (ENSA)
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Summary
This video is an introduction to Module 1 of the CCNA3 course, focusing on Single Area OSPFv2 Concepts. It explores the fundamental aspects of OSPF, a link-state routing protocol designed for distributing IP routing information within a single autonomous system. The lecture breaks down OSPF's operations, such as packet types, database structures, and routing algorithms like SPF. It also distinguishes between single-area and multi-area OSPF, explaining their roles in optimizing network efficiency. OSPF Version 3, used for IPv6, is briefly covered. The lesson encapsulates OSPF's procedure for achieving network convergence, highlighting the significance of designated routers in multi-access networks.
Highlights
Introduction to OSPF - a crucial IP routing protocol developed as an alternative to RIP. 🌟
Understand how OSPF operates in point-to-point and multi-access networks. 🤝
Breakdown of OSPF packet types, including hello and link state updates. 📦
OSPF databases: Adjacent, Link State, and Forwarding databases explained. 🗄️
Exploration of the SPF algorithm used by OSPF to determine best routing paths. 🚀
Single vs Multi-area OSPF: Differences and benefits for network scalability. 🖥️
Introduction to OSPF Version 3 for IPv6 networks. 🌐
Key Takeaways
OSPF is a link-state routing protocol that helps in faster convergence and is scalable for larger networks. 🌐
Single-area OSPF simplifies the network design, while multi-area OSPF offers scalability by dividing the routing domain. 🔄
OSPF Version 3 supports IPv6 routing, adding flexibility for modern networks. 🔧
Overview
Welcome to this engaging session on Single Area OSPFv2 Concepts! 🌟 We'll journey through OSPF, exploring its important role in distributing IP routing information within networks. Think of it as the glue that binds our routers together, creating a smoother and more efficient internet experience for everyone.
Our focus here is on understanding the nitty-gritty of how OSPF functions. From distinguishing packet types like hello and database description packets to unraveling the complex OSPF databases, we're here to make these technicalities as breezy as a walk in the park. 🤓 And don't worry, we've got your back with insights on understanding link state advertisements and executing the SPF algorithm!
Lastly, we're diving into the worlds of single and multi-area OSPF. 📜 What's the buzz about OSPF Version 3 for IPv6? We've got that covered too. This module sets the stage for mastering networking protocols - because being tech-savvy isn't just cool, it’s essential in our digital age. Dive in and let's geek out together!
CCNA3 Module 1: Single Area OSPFv2 Concepts - Enterprise Networking Security and Automation (ENSA) Transcription
00:00 - 00:30 welcome to the cisco netacad ccna 3 enterprise networking security and automation lecture series this is our first lecture for this course and if you haven't seen my previous lecture series covering ccna1 and ccna2 i will leave links in the description for those playlists i would recommend that you go through previous ccna lectures before moving forward with this ccna 3 course
00:30 - 01:00 today i will cover module number 1 which is single area ospf version 2 concepts the primary objective of this module is to explain how single area ospf operates in both point-to-point and broadcast multi-access networks we will cover ospf features and characteristics so that you can describe the basic ospf features
01:00 - 01:30 we will cover ospf packets and ospf operation ospf features and characteristics so the ospf stands for uh the open shortest path first protocol which is a family of ip routine protocols and it is an interior gateway protocol also known as igp for
01:30 - 02:00 the internet which is used to distribute ip routing information throughout a single autonomous system also known as aas in the an ip network as we go through this course we will get into the details of how you can set up ospf network and how the open shortest path first protocol act on different configurations
02:00 - 02:30 so the ospf is a link state routing protocol that was developed as an alternate for the distance vector routing information protocol also known as rep ospf has significant advantages over rip in that it offers faster convergence and scales to much higher network implementations sorry much larger network implementations so the ospf is a link state routing protocol that uses the concept of areas
02:30 - 03:00 the network administrator can divide the routing domain into distinct areas that help control routing update traffic a link is an interface on a router a network segment that connects two routers or a stub network such as an ethernet lan that is connected to a single router information about the state of a link is known as a link state
03:00 - 03:30 all link state information includes the network prefix prefix length and cost this module cover the basic single area ospf implementations and configurations so what are the components of ospf all routing protocols share similar components they all use routing protocol messages to exchange route information the messages help build data structures
03:30 - 04:00 which are then processed using a routing algorithm routers running ospf exchange messages to convey routing information using five types of packets those are hello packets database description packet link state request packets link state update packet and link state acknowledgement packet these packets are used to discover
04:00 - 04:30 neighboring routers and also to exchange routing information to maintain accurate information about the network in this course it is important that you understand what each of these packets do so we'll go over that in a little bit of more detail in next few slides so you need to understand how ospf hello packet is different from the database description packet and different from the other link states packets so you should be able to
04:30 - 05:00 differentiate and understand the functions of these packets as we go through these lectures ospf messages are used to create and maintain three ospf databases they include adjacency database link state database and forwarding database the adjacency database has a table called the neighbor table and it lists of all neighbor routers to
05:00 - 05:30 which a router has established bi-directional communication this table is unique for each router and can be viewed using show ipospf neighbor command in your cisco routers so if you have a cisco router with ospf setup you can run the show ip ospf neighbor command and that will get you the table for the adjacency you know database
05:30 - 06:00 the next database is the link state database also known as lsdb which is a topology table that lists information about all other routers in the network the database represents the network lsdb all routers within an area have identical lsdb the link state database and can be viewed using the command show ipospf database so if you have a cisco
06:00 - 06:30 router you can run the show ipospf database and that will give you the lsdb the forwarding database contained the routing table that includes a list of routes generated when an algorithm is run on the link state database each routes sorry each router's routing table is unique and contain information on how and where to send packets to the other routers
06:30 - 07:00 this can be viewed using the show ip route command so if you have a a cisco router you can run the show ip route command with the ospf setup and you can view the forwarding database so the forwarding database have the routing table and those list of routes are generated using an algorithm that is when it is run based on the you know that link state database so it is this database routing
07:00 - 07:30 table is built on the the database from up here the router builds the topology table using results of calculations based on the distress shortage past first algorithm also known as spf algorithm the spf algorithm is based on the cumulative cost to reach a destination the spf algorithm creates an spf tree
07:30 - 08:00 by placing each router at the root of the tree and calculating the shortest path to the each mode the spf tree is then used to calculate the best routes ospf places the best routes into the forwarding database which is used to make the routing table so that's the process of creating the routing table is use the spf algorithm
08:00 - 08:30 so that's a key component of the ospf link state operation to maintain routing information ospf routers complete a generic link state routing process to reach a state of convergence because the main purpose of using a protocol like ospf is for faster convergence so this is one of the primary functions
08:30 - 09:00 the following are the link state routing steps that are completed by a router it establishes neighbor adjacent adjacencies it exchange link state advertisements it builds the link state database it execute the spf algorithm then it will choose the best route so these are the steps that needs to go through that to create the link state you know
09:00 - 09:30 the the routing information single area and multi-area ospf to make ospf more efficient and scalable ospf support hierarchical routing using areas an ospf area is a group of routers that shares the same link state information in their lsdb so if somebody asks you what is an ospf area that is the definition of ospf area
09:30 - 10:00 so spf area is a group of routers that shares the same link state information in their lsdb ospf can be implemented in one of the two ways that includes single area ospf where all routers are in one area which is comes with the best practice with the use of area 0 or the multi area ospf where ospf is
10:00 - 10:30 implemented using multiple areas in a hierarchical fashion all areas must connect to the backbone area known as typically the area 0 and routers interconnecting the areas are referred to as area border routers also known as abrs you will hear that term and these concepts a lot as we go through this lecture series the focus of this module is on single
10:30 - 11:00 area ospf version 2. so while the focus of this module is the single area ospf version 2 as we go through this lecture series i may cover topics that related to multi-area as well multi-area ospf the hierarchical topology design options with multi-area ospf can offer the
11:00 - 11:30 following advantages smaller routing tables tables are smaller because there are fewer routing table entries this is because network addresses can be summarized between areas route summarization is not enabled by default reduce link state update overhead so designing multi area ospf with smaller areas minimize the processing and memory requirements of the each of those routers
11:30 - 12:00 reduce frequency of spf calculations the multi-area ospf localized the impact of a topology change within an area for instance it minimizes routing update impact because lsa flooding stops at the area boundary ospf version 3. so the ospf version 3 is the ospf
12:00 - 12:30 version 2 equivalent for exchanging ipv6 prefixes ospf version 3 exchanges routing information to populate the ipv6 routing table with remote prefixes so this is a key information that you should remember the ospf version 3 is for ipv6 routing note with the ospf version 3 address families feature ospf version 3 includes support for both
12:30 - 13:00 ipv4 and ipv6 ospf address families is beyond the scope of this curriculum so general ospf version 3 is for ipv6 but ospf version 3 with address families feature will enable you to use ospf version 3 for both ipv4 and ipv6 but we will not cover that in this lecture series
13:00 - 13:30 ospf version 3 has the same functionality as ospf version 2 but uses ipv6 as the network layer transport communicating with ospf version 3ps and advertising ipv6 routes ospf version 3 also uses the spf algorithm as the computation engine to determine the best paths throughout the routing domain ospf version 3 has separate processes
13:30 - 14:00 from its ipv4 counterpart the processes and operations are basically the same as in the ipv4 routing protocol but run independently so that's all you need to know about ospf version 3 for now in this class ospf packets there's a video called ospf packets that
14:00 - 14:30 nicely laid out how these uh ospf you know works with the hello packet database description the link state requests etc etc if you do not have a copy for this video through your cisco netacad or to your academic institution i will post a link in the description for this video as well as a card on the top right hand corner so you can go ahead and click on it on my youtube channel so you can watch
14:30 - 15:00 it i would recommend that you watch this video before you move forward because that will give you a basic idea about what we're gonna about what we about to cover types of ospf packets so this table summarizes the five different types of link state packets also known as lsps used by ospf version 2. the ospf version 3 has similar packet types but we won't be covering that in this module
15:00 - 15:30 so if you have watched the previous video that i mentioned you can watch on my youtube channel or through your netacasis connecticut you probably came across the hello packets the database description one the link state request the link state update and the link state acknowledge so the hello packet discovers neighbors and builds adjacencies between them it's like saying hello you know these are the my information what's you know things like you know communicating between the you know the devices neighbors so
15:30 - 16:00 it's just like saying hello to someone you know so the database description or dbd checks for database synchronization between routers the link state request also known as lsr requests specific link state records from router to router link state update also known as lsu sends specifically requested link state records link state acknowledgement also known as
16:00 - 16:30 ls arc acknowledges the other packet types so this basically acknowledges the receiving of these packets link state updates lsus are also used to forward ospf routing updates an lsu packet can contain 11 different types of ospf version 2 lsas ospf version 3 renamed several of these lsas and also contains two additional
16:30 - 17:00 lsas lsu and lsa are often used interchangeably but the correct hierarchy is lsu packets contain lsa messages so that's a key important thing that you should remember for your exam lsu and lsa are often used interchangeably however for your exams and for understanding the concepts you need to realize that the correct hierarchy is lsu package contains lsa
17:00 - 17:30 messages so on the right hand side it shows some information about ls use and lsas so basically lsu's includes hello uh dbd lsr lsu and lsr and within the ls u you will have the lsa information so remember that the lsu packets contain the ls a messages
17:30 - 18:00 so let's look at the hello packet so the ospf type one packet is the hello packet remember uh from our previous uh slide with the table which has one two three four on the side i believe so the first the type 1 packet is also the hello packet is also known as the type ospf type 1 packet hello packets are used for the following to discover ospf neighbors and establish
18:00 - 18:30 neighbor adjacencies advertise parameters on which two routes must agree to become neighbors elect and designate router also known as dr and backup designated router or bdr on multi-access network like ethernet point-to-point links do not require dr obdr so it's for multi-access purposes it will also the hello packet will be used for dr and bdr designations
18:30 - 19:00 so on the right hand side we have this diagram that you probably have seen if you watched that video that the external video from cisco that i have posted to my youtube channel and it shows that the ospf packet header and the ospf packet type specific data which all contain the hello packet and uh this is what the breakdown of that the ospf packet header um and the hello packets uh what it look
19:00 - 19:30 like so you have the hello interval and you have an option and then you have the route priority and the interval and all the other information associated with that ospf hello packets and you can see that on this diagram and for your exams and quizzes for you probably don't need to know everything in here however if you want to be good at what you do and if you want to understand the concept of ospf you should be able to
19:30 - 20:00 understand what's shown on here right so as we go through this course i know this is the very first lecture right now but as we go through this course you will come you will have a complete understanding of why not why like how these um you know packet headers and the packet information are important to ospf routing okay so for now just know this is basically how it look like
20:00 - 20:30 ospf operation there's another video called ospf operation which i'll be covering in next few slides if you have access to this video through cisco netacad or through your academic institution you can go ahead and watch them or i have a copy of that video posted to my youtube channel and i will leave a link in the description as well as a card on the top right hand corner and again watching these videos will enhance your understanding of concepts
20:30 - 21:00 that we will cover in next few slides ospf operational states down state so the down state is no hello packets receive that mean it is down the router sends hello packets transition into the int any state so if if there are no hello packets received the router sends hello packets however it will eventually go into the transition into
21:00 - 21:30 init state init state hello packets are received from the neighbor they contain the router id of the sending router transition to two-way state two-way state in this state communication between the two routers is bi-directional on multi-access links the routers elect a dr and bdr remember area border routers
21:30 - 22:00 so transition that in at this stage into ex start or x start state so the x start state at this stage what happen is on point to point networks the two routers decide which router will initiate the dbd packet exchange and decide upon the initial dvd packet sequence number exchange state routers exchange dbd packets if
22:00 - 22:30 additional routing information is required then the transition into the loading otherwise transition into full state so the loading state would happen if the additional you know information is required it it has the lsr and lsus are used to gain additional route information and the routes are processed using the spf algorithm as expected as we are in ospf
22:30 - 23:00 which is uses the spf algorithm and transition at this point it wants it to obtain that information into full state so it could go from exchange to full sales exchange state to full state or you could go from exchange states to loading state to full state at full state the link state database of the router is fully synchronized and the ospf operation in here has been completed
23:00 - 23:30 establish neighbor adjacencies to determine if there is an ospf neighbor on the link the router sends a hello packet that contains its router id out all ospf enable interfaces so to determine the ies and ospf neighbor on the link what the router going to do is going to send that hello packet that contains its router id out all of its ospf enable interfaces
23:30 - 24:00 the hello packet is sent to the reserved all ospf routers ipv4 multicast address of 244c.0.05 because in ospf configuration this would be the multicard of ipv4 multicast address for all ospf routers 244.0.05 only ospf version 2 routers will process
24:00 - 24:30 these packets the ospf router ide is used by the ospf process to uniquely identify each router in ospf area a router id is a 32-bit number formatted like an ipv4 address and assigned to uniquely identify a router among ospf peers when a neighboring ospf enable
24:30 - 25:00 sorry when a neighboring ospf enabled router receives a hello packet with a router id that is not within its neighbor list the receiving router attempts to establish an adjacency with the initiating router so that's how the neighbor adjacencies work so in the next page we will look at how the process working in a little bit of more detail so the process routers used to establish adjacency on a multi-access network in
25:00 - 25:30 this case we're going to have these four steps the down init state so when the ospf version 2 is enabled on the interface the r1 transitions from down to init and start sending ospf v2 version 2 hollows out the interface in an attempt to discover neighbors in the init state when the r2 receive a hello from the previous unknown router
25:30 - 26:00 r1 it adds the r1's router id to the neighbor list and respond with a hello packet containing its own router id the two-way state r1 receives r2's hello and notices that the message contain r1 route id in the list of our two neighbors r1 adds r2 shroud id to the neighbor list and transitions to the two-way state if r1 and r2 are connected with a
26:00 - 26:30 point-to-point link they transition to x-start state if the r1 and r2 are connected over a common ethernet network the dr and db sorry bdrc election process will occur elect the dr and bdr the dr and bdr election occurs where the router with the highest router id or
26:30 - 27:00 the highest priority is elected as the dr and the second highest is the bdr so area border routers right remember the the dr's and bdrs we covered in previous slides so this is the backup this is the primary synchronizing ospf databases after the two-way state progress
27:00 - 27:30 transition to database synchronization states this is a three-step process so those steps includes decide first router so the router with the highest router id sends its dbd first because it's the one that gonna get precedence exchange dvds so as many as needed to convey the database the other routers
27:30 - 28:00 must acknowledge each dbd with ls arc packet that's the acknowledgement packet remember send an lsr each router compares the dbd information with the local lsdb with the dbd has more current link information if the if the dvd has more current link information the router transition into the loading state yes this will show up on your exam so
28:00 - 28:30 make sure you know this these concepts so i'm just quickly going through some of the lectures but i will give you a more comprehensive uh idea about how they work on a real live lab demonstration as well but remember these steps it does matter for your exams so after all lsr have been exchanged and satisfied the routers are considered synchronized and in a full state and then it the updates are sent which
28:30 - 29:00 are less use so when an exchange is preserved perceive sorry an incremental update would happen and about every 30 minutes so that is the synchronization of ospf databases the need for a designated router or dr multi-access networks can create two challenges for ospf regarding the flooding of lsas as follows
29:00 - 29:30 creation of multi-apple adjacencies ethernet networks could potentially interconnect many ospf routers over a common link creating adjacencies with every router would lead to an excessive number of lsa exchange between routers on the same network so it's going to create more overhead extensive flooding flooding of lsas the link state routers flood their lsas
29:30 - 30:00 anytime ospf is initialized or when there is a change in the topology this flooding can become ssu as well lsa flooding with a designated router or dr an increase in the number of routers on a multi-access network also increases the number of lsa exchange between the routers this flooding of lsas significantly impact the operation of ospf
30:00 - 30:30 if one router in a multi-access network had to flood and acknowledge all received lsas to all other routers on that same multi-access network the network traffic would become quite chaotic so that is really bad so on multi-access networks ospf elects a designated router also known as dr to be the collection and distribution point
30:30 - 31:00 for lsa sent and received a dbr is also elected in case the dr fails all other routers become d d are others a dr other is a router that is neither the dr which is a designated router nor the bdr the backup designator router please note the dr is only used for the
31:00 - 31:30 dissemination of lss the router will still use the best next hop router indicated in the routing table for forwarding all other packets so the dr which is a designated router or in if it fails the bdr will only be used for decimation of the lsa so it doesn't use for all other packets it's just for the lsa messages or the packets right so that would bring us to the end of
31:30 - 32:00 this lecture and now i will go over a summary of what we have covered we learn that open shortest path first also known as ospf is a link state routing protocol that was developed as an alternative for distance vector routing information protocol also known as rip ospf is a link state routing protocol that uses the concept of areas for scalability
32:00 - 32:30 a link state is an interface on a router a link is also a network segment that connects two routers or a stub network such as ethernet lan that is connected to a single router all link state information includes the network prefix prefix length and cost all routing protocols use routing protocol messages to exchange route
32:30 - 33:00 information the messages help build data structures which are then processed using a routing algorithm routers running ospf exchange messages to convey routing information using five types of packets they include the hello packet the database description packet the link state request packet the link state update packet the link state acknowledgement packet
33:00 - 33:30 ospf messages are used to create and maintain three ospf databases they include the adjacency database uh which creates the neighborhood table the link state database which also known as lsdb creates the topology table and the forwarding database which creates the routing table the router builds the topology table using results of calculations based on
33:30 - 34:00 the spf which is the shortest path first algorithm the spf algorithm is based on the cumulative cost to reach a destination in ospf cost is used to determine the best path to destination so we use the cost as the you know the the calculation you know key for determining the best part for destination we also learn to maintain the routing
34:00 - 34:30 information the ospf routers complete a generic link state routing process to reach a state of convergence establish native adjacencies exchange link state advertisement build the link state database execute the spf algorithm choose the best uh route so the dosa you know the you know the basic steps that it takes and then use
34:30 - 35:00 with single area ospf any number can be used for the area but however it is the best practice to use area 0 with single area ospf with multi area ospf one large routing domain can be subdivided or divided into smaller areas to support hierarchical routing routing still occurs between the areas also known as inter area routing
35:00 - 35:30 um and while many of the process processor invasive routine operations such as recalculating the database are kept within that area ospf version 3 is the ospf version 2 equivalent for exchanging ipv6 prefixes and recall that the ipv6 the network address is referred to as the prefix and the subnet mask is called the prefix length
35:30 - 36:00 ospf uses the following link state packets also known as lsps to establish and maintain neighbor adjacencies and exchange routing updates and we learn about the hello dbd lsr lsu and ls arc and i mentioned that it is one two three four five so it's you know you can say you know it's a type one if somebody say it's a type one uh ospf packet which is a hello packet for example lsus are used
36:00 - 36:30 to forward ospf routing updates such as links changes hello packets are used to discover ospf neighbors and establish neighbor adjacencies advertise parameters on which two routers must agree to become neighbors and elect the designated router also known as dr and backup designated router also known as bdr on multi-access network like ethernet point to point links do not require dr
36:30 - 37:00 obdr we also learned some important fields in the hello packet types are the route id area id network mask hello interval router priority dead interval dr bdr and list of neighbors and i showed a diagram of that you know the packet on on the screen on the screen but that video you know the the complimentary video that i have posted from cisco that also go into depth of you know
37:00 - 37:30 looking at those um that packet and you know pulling apart that packet and try to explain that to the students you know how that packet works so i would recommend that if you don't remember like i went too fast with this lecture you can go ahead and watch that video to understand uh and get a better handle of the the the configuration of the hello packet the states that ospf progresses through to
37:30 - 38:00 do reach convergence um downstate init state two-way state x-start state exchange state loading state and full state and we learn that when ospf is enabled on an interface the router must determine if there is another ospf neighbor on the link state by sending a hello packet that contains its router id out all ospf enable interfaces the hello packet is sent to the res
38:00 - 38:30 reserved all ospf router ipv4 multicast address which is the 244.0.05 however only ospf version 2 routers will then process these packets when a neighboring ospf enable router receives a hello packet with a router id that is not within enable list the receiving router attempts to establish an adjacency with the initiating router
38:30 - 39:00 after the two-way states routers transition to database synchronization states which is then three uh steps a process right multi-access networks can create two challenges for ospf regarding the flooding of lsas the creation of multiple adjacencies and extensive flooding lsa so that's the you know multi-area networks can create so one of the challenges with multi-area network
39:00 - 39:30 ospf's we learn a dramatic increase in the number of routers also dramatically increases the number of lsas exchange between the routers this flooding of lsas significantly impact the operation of ospf and if every router in a multi-access network had to flood and acknowledge all receivable essays to all other routers
39:30 - 40:00 on the same multi-access network the network traffic would become quite chaotic in other words it's going to get bogged down and you're going to have some overhead this is why the dr the designator router and bdr the backup designated router election is necessary on multi-access networks ospf elects adr to be the collection and distribution point for lsas sent and received a bdr or backup designator router is
40:00 - 40:30 also elected in case the designator router fails so that would cover the summary for everything that we have covered in this lecture if you like these type of lectures please thumbs up this video and subscribe to my channel i know i went through this lecture little bit too fast and i haven't gone through any of the lab materials and or explain ospf in depth using lab examples
40:30 - 41:00 so i stay tuned i will post those in next few weeks until next time good luck with your exams and have a nice day