Total 10 Blogs

Created by - Stanley Avery

OSPF Neighbor States

OSPF, or Open Shortest Path First, is a popular routing protocol used in many networks today. One of the benefits of using OSPF is its ability to dynamically determine the best path to send traffic. In this post, we'll take a look at the different OSPF neighbor states that can be seen in a network and what they mean. What is OSPF and Why do you need it? OSPF is a routing protocol commonly used in network settings. It allows multiple devices within a network to communicate and exchange data by finding the most efficient paths for transmission. This helps to prevent network congestion and maintain optimal performance. OSPF also allows for scalability, allowing it to adjust easily as networks expand or change. In addition, it offers high levels of security through authentication measures. While there are other routing protocols available, OSPF has proven to be a reliable and efficient option for many organizations. When implementing a new network infrastructure, considering the needs and capabilities of various routing protocols can help ensure smooth and successful operation. What does "OSPF Neighbor States" mean? In order for OSPF to function properly, neighboring routers must exchange information and establish a neighbor state with one another. These OSPF neighbor states are crucial for establishing successful communication between routers and determining the best pathways for data transmission. The eight possible OSPF neighbor states are Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full. Let's talk about these OSPF neighbor states in detail. 1. Down: The first of many OSPF neighbor states is "down." When a device is in the "down" state, it means that there is currently no hello package being received from that device. This could be due to a physical issue, such as a broken network cable, or a software issue, such as incorrect configuration parameters. In any case, it is important to troubleshoot and resolve this issue as quickly as possible, as it can greatly impact the network’s overall performance. 2. Attempt: In a network, the "attempt" OSPF state is only applicable in a non-broadcast multi-access (NBMA) environment. In this type of network, routers use unicast hello packages to establish adjacencies with their neighbors. The "attempt" neighbor state indicates that a router has received a hello package and is attempting to become neighbors with the sending router. 3. Init: In OSPF networking, "init" refers to a neighbor state in which a hello package has been received, but no router ID has been received. This generally indicates that the exchange of information between routers has just begun, and the network is still in the process of establishing connections. 4. 2-Way: "2-way" as an OSPF state refers to bi-directional communication between routers. In order for two routers to become neighbors, they must first establish bi-directional communication and exchange Hellos. Once bi-directional communication has been established, the neighbor state will show as "2-way." From there, the routers exchange link state information and form adjacencies, ultimately creating a fully functional OSPF network. Additionally, BDs and BDRs are elected at the end of this stage. 5. Exstart: The "Exstart" state in OSPF neighbor relationships means that both parties have agreed to exchange link state information, and a master-slave relationship has been established. In this state, the exchange of link state information begins and continues until both parties declare that they have nothing further to exchange. It is important for OSPF routers to exchange this information so they can accurately calculate the best paths for data transmission between networks. 6. Exchange: In the OSPF routing protocol, the exchange neighbor state is when two routers exchange Database Description (DBD) packets. This exchange contains information about the router's links and their associated metrics. Once this exchange is complete, the routers move on to the loading state, where they exchange Link State Advertisements (LSAs) and build their topology maps. The exchange state is an important step in establishing a neighbor relationship and ensuring that both routers have the same information. It is vital for proper communication and routing within a network. 7. Loading: "Loading" indicates that the actual link state exchange is taking place. This means that the router is sending and receiving Link State Advertisements (LSAs) through designated neighbors, with the aim of building a comprehensive Link State Database. Once this process is completed, the neighbor state will change to "Full," indicating that all link state information has been exchanged successfully. 8. Full: "Full," as one of the OSPF neighbor states, refers to routers that are fully adjacent to each other and have fully synchronized their link-state databases. This is the normal and desired state for routers in an OSPF network, as it ensures efficient communication and routing. In contrast, a router in the "Init" or "Down" neighbor state may indicate a problem with connectivity or configuration. So while seeing routers in a "Full" state may not be exciting news, it is essential for smooth network operation. To Sum Up: OSPF Neighbor States is an important chapter in understanding the working of OSPF. The article provides a comprehensive summary of the states that a neighbor can be in and how routers behave under different conditions. We hope you found this information useful. If you are interested in learning more about networking or need to refresh your skills, we offer excellent CCIE Enterprise Infrastructure course on our IT courses list.

Published - Sun, 13 Nov 2022

Created by - Stanley Avery

What is OSPFv3? How does it work?

Versions of the Open Shortest Path First (OSPF) protocol are used in a wide variety of networking applications. You may be familiar with OSPF as a routing protocol, but did you know that there is also an OSPFv3 version? This newer version provides many enhancements, including support for IPv6 networks. Let's take a closer look at what OSPFv3 is and how it can benefit your network. What is OSPFv3? OSPFv3, also known as Open Shortest Path First version 3, is a routing protocol used in Internet Protocol version 6 (IPv6) networks. In contrast to its predecessor, OSPFv2, which is used in IPv4 networks, OSPFv3 supports IPv6 address types and deepens the authentication options available in the protocol. It also allows for the efficient flow of traffic by improving the calculation and distribution of routes within a network. Despite the benefits offered by the newest version, it remains important for network administrators to carefully consider whether implementing this protocol is necessary for their particular network environment. Ultimately, selecting the most appropriate routing protocol will help ensure smooth operation and maximum performance for a network. What is IPv6? The Internet Protocol, or IP, is the set of rules and guidelines that determine how devices connect and communicate on a computer network. The current version, IPv4, has been in use since the early 1980s and can support a limited amount of unique device addresses. In order to accommodate the increasing number of devices connected to the internet, a new version was developed: IPv6. IPv6 allows for significantly more unique device addresses, creating room for future growth. It also offers improved security features and better support for mobile devices. While most devices currently use IPv4, many internet service providers have begun the process of transitioning to IPv6 to prepare for future demands on the network. Overall, IPv6 offers improved functionality and capacity for connected devices. OSPFv3 vs OSPFv2: What are the biggest changes? When determining which version of OSPF to use for your network, it's important to understand the key changes between OSPFv3 and OSPFv2. One of the biggest updates includes support for IPv6 addresses. This means that OSPFv3 can handle both IPv4 and IPv6 addresses, while OSPFv2 is limited to solely IPv4 addresses. Another significant change is the addition of OSPFv3 authentication for link-local communications, providing an extra layer of security. It also allows for more flexibility when configuring areas and interfaces and improved standardization across different vendors' implementations. However, it's important to note that not all devices support OSPFv3 yet, so compatibility should be considered before implementing it in your network. Overall, the updates in OSPFv3 make it a strong choice for modern networks dealing with both IPv4 and IPv6 addresses, but careful consideration and planning should be taken before transitioning from OSPFv2. Tips: You must to check this course for more information about OSPF. OSPFv3 LSA Types As an important component of OSPFv3, Link State Advertisements (LSAs) provide information about the network topology. There are several different types of LSAs that serve unique purposes. The router LSA, for example, contains information about OSPFv3-enabled routers and their directly-connected links. Network LSAs provide information about multi-access networks, while inter-area prefix LSAs advertise summary route information between areas. As another example, autonomous system external LSAs advertise external routes from other routing protocols. It is crucial for routers to have accurate and up-to-date LSA information in order to calculate the best path through the network. LSAs also have a sequence number and lifespan to ensure this consistency, allowing for efficient refreshes and updates. Understanding the various LSA types and their functions is essential for the successful deployment of OSPFv3. To Sum Up OSPF v3 is a significant upgrade to the previous versions of the protocol. It provides more options for configuration and has been updated to work with IPv6 networks. If you’re using OSPF in your network, it’s worth upgrading to v3.

Published - Thu, 10 Nov 2022

Created by - Stanley Avery

OSPF Virtual Link

OSPF virtual links are a great way to connect two or more OSPF networks together. In this blog post, we'll discuss everything you need to know about virtual links, including how they work and the best way to configure them. We'll also cover some of the common problems that can occur with virtual links and how to fix them. So if you're looking to learn more about OSPF virtual links, read on! What Is an OSPF Virtual Link? OSPF (Open Shortest Path First) is a networking protocol used for routing in large, complex networks. It is frequently used in internet service provider environments because of its scalability and ability to calculate the fastest route for data packets. In some cases, it may be necessary to establish a connection between two OSPF areas that cannot be physically connected due to geographical distance or lack of available network resources. This is where OSPF virtual links come into play. All Open Shortest Path First (OSPF) autonomous system zones must be physically connected to the backbone area (Area 0). In some circumstances where this is not possible, you can use a virtual link to connect to the backbone through a non-backbone zone. In other words, an OSPF virtual link is a logical path that connects two areas of a network through an area that does not have a physical connection. This allows for the network to function as if all areas were physically connected, despite possibly having non-contiguous layouts. Virtual links can also be authenticated for added security measures. It should be noted that virtual links are not permanent solutions, and networking specialists should find a more permanent solution as soon as possible. What Are Some Possible Scenarios Where You Might Need an OSPF Virtual Link? In a large network, connecting all areas using a single Area 0 (also known as the backbone area) can sometimes be difficult. OSPF virtual links allow you to create a logical connection between two non-contiguous areas, essentially creating a tunnel through the backbone area. One possible scenario where an OSPF virtual link may be necessary is when there is a partitioned backbone area within a network. This can occur if there is a break in the physical connection between two routers within the backbone area, but there still needs to be communication between them. Another scenario where this may be necessary is if physical barriers, such as oceans or mountains, prevent direct connections between the areas. Another possibility is if there are separate organizations with their own OSPF network and areas, but they need to communicate with each other. In both cases, an OSPF virtual link can provide a workaround solution and ensure uninterrupted communication within the larger network. How do OSPF Virtual Links work? To establish a virtual link, one of the routers must be designated as the virtual link endpoint, and a router in the backbone area must act as the transit router. The virtual link endpoint router then establishes a virtual adjacency with the transit router, allowing it to exchange routing information through the backbone area. Virtual links can also be used in cases where there is an unwanted physical path between two areas, and OSPF can automatically detect and establish a virtual link instead. However, it's important to note that virtual links should be carefully planned and monitored, as they increase the complexity of OSPF network configurations. You can find more in-depth information on OSPF virtual link configuration here. Final Words OSPF virtual links are a powerful tool for networking specialists. By understanding how they work and how to configure them, you can make your networks more reliable and efficient. We hope this article has helped you learn everything you need to know about virtual links in OSPF. If you have any questions or would like more information, please click here and learn everything about OSPF.

Published - Thu, 10 Nov 2022

Created by - Stanley Avery

OSPF DR Election - The Whys and The Hows

Are you familiar with the OSPF DR election process? If not, or if you're just looking for a refresher, read on! This article will explain what DR elections are, why they happen, and how routers determine who will become the DR. We'll also discuss some of the factors that can influence the outcome of a DR election. So whether you're an experienced OSPF user or just getting started, this post has something for you! Before Moving On: What Is OSPF DR (Designated Router)? The Open Shortest Path First (OSPF) protocol is used in computer networking to find the shortest path between network nodes. The OSPF protocol uses a link-state algorithm, meaning each node maintains a database of all available routes and their associated costs. When a node wants to find the shortest path to another node, it simply looks up the best route in its database. Designated Routers (DRs) are essential in OSPF protocol networks. The Designated Router (DR) and a Backup Designated Router (BDR) in OSPF play the role of a central point for exchanging OSPF information between many routers on the same multiaccess broadcast network segment. Non-DR and non-BDR routers only need to exchange routing information with the DR and BDR rather than every router on the segment. As you can see, DRs play a vital role in ensuring that networks using the OSPF protocol remain operational. So, How Does OSPF DR Election Work? As mentioned above, for an Open Shortest Path First (OSPF) router to become a Designated Router (DR), it must first go through an election process. This process starts when each router on the network sends out a Hello message. The Hello message contains information about the router's identity, priority, and options. The router with the highest priority becomes the DR, while the router with the second highest priority becomes the Backup Designated Router (BDR). If two routers have the same priority, then the one with the higher router ID becomes the DR. Once the DR and BDR have been elected, they begin exchanging routing information with each other to maintain synchronized copies of the routing table. If the DR fails, then the BDR takes over its responsibilities. The election process always ensures that a DR and BDR are available to exchange routing information and keep the network running smoothly. We should add that you can configure the DR/BDR selection by manually designating priority to routers. A Quick Recap of the OSPF DR Election: “ip ospf priority” command is used for setting the priority on the router interface. The default priority is always 1. Priority 0 means that the router will never be selected DR or BDR. The “clear ip ospf process” command must be used in order for changes to be effective.You can find well-prepared documents about OSPF DR and BDR Electionin our CCIE Enterprise Infrastructure Course. Final Words DR elections are a critical part of the OSPF protocol, and it is important to understand why they happen and how they work to troubleshoot any issues. By understanding the mechanics of the election process, you can help ensure that your network runs smoothly. Also you can learn more about the OSPF DR election and more at Cisco's OSPF Design Guide here.

Published - Wed, 12 Oct 2022

Created by - Stanley Avery

OSPF Cost - Everything You Need to Know

OSPF (Open Shortest Path First) is a link-state routing protocol that uses a cost metric to calculate the best route between two nodes. In this article, we'll look at how OSPF calculates costs and discuss some of the factors that can influence them. So, if you're curious about how OSPF's cost calculation works or want to learn how to tweak its settings for your network, read on! What is "OSPF Cost"? OSPF cost is a metric used by the OSPF routing algorithm to calculate the best path between two OSPF-enabled devices. The cost of a path is determined by adding up the costs of the individual links that make up the path. The cost of a link is typically expressed in terms of bandwidth. In most cases, the cost of a link is inversely proportional to its bandwidth. As a result, OSPF-enabled devices will typically prefer paths with high-bandwidth links. How is OSPF Cost Calculated? The OSPF cost is calculated based on the link's bandwidth and is used by the OSPF algorithm to determine the best path between two routers. The higher the bandwidth, the lower the cost. The lower the cost, the more preferable the link. In most cases, the OSPF cost is calculated automatically by the router. However, sometimes, it may be necessary to set the OSPF cost manually. To do this, use the ip ospf costcommand. The value entered with this command will be used as the link's OSPF cost. Keep in mind that this value must be an integer between 1 and 65535. If it is not, the router will revert to using the default OSPF cost calculation. The OSPF Cost is calculated by using this formula: reference bandwidth /interface bandwidth. Here Are the Default Costs Bandwidth - Cost Gigabit Ethernet Interface (1 Gbps) - 1 Fast Ethernet Interface (100 Mbps) - 1 Ethernet Interface (10 Mbps) - 10 DS1 (1.544 Mbps) - 64 DSL (768 Kbps) - 133 A Little Problem As you can see, OSPF considers all interfaces with a bandwidth of 100 Mbps or more as equal. The best possible cost is always 1. So no matter the speed of the internet, it will all have a default cost of 1 when it is over 100 Mbps. This can create subpar routing in up-to-date networks that use current high-speed ethernet interfaces. It is possible to force a router to use a faster route manually. To change the reference bandwidth in an OSPF network, use the following command: router ospf 1 reference-bandwidth Where is the desired reference bandwidth in Mbps. For example, to configure the reference bandwidth to 1 Gbps, use the following command: router ospf reference-bandwidth 1000 By doing this, you can ensure that your routers will pick the fastest route possible. You must to check CCIE Enterprise training about all useful commands of OSPF. Under What Circumstances Might You Need to Manipulate OSPF Metrics? In a typical OSPF network, the cost is automatically calculated based on the bandwidth of the link. However, there are times when it may be necessary to manipulate the cost metric manually. For example, if two links have different bandwidths, but the router considers them to be equally reliable, it may make sense to increase the cost of the lower bandwidth link to reduce traffic on that link. In another example, if one link is consistently congested while another is not, it may be necessary to decrease the cost of the congested link to encourage more traffic to use that link. These are just a few examples of when it might be necessary to manipulate OSPF cost metrics; in general, any time there is an imbalance in traffic or reliability between two links, manipulating the cost metric can help to restore balance. You can learn more about OSPF costs and other topics on Cisco's Design Guide

Published - Wed, 12 Oct 2022

Created by - Stanley Avery

OSPF Redistribution: Quick Guide

Redistribution is a process that allows you to share routing information between different routing protocols. This can be a helpful tool if you want to use more than one protocol on your network.In this article, we will take a quick look at how OSPF redistribution works. We will also discuss some benefits and drawbacks of using redistribution in an OSPF network. What Exactly is OSPF Redistribution? Before going into OSPF redistribution, we should briefly discuss what OSPF (Open Shortest Path First) is. It is a routing protocol to find the shortest path between two devices on a network. It is a link-state protocol, which means that it keeps track of the state of the network links and calculates the best route based on that information. OSPF is a widely used routing protocol. It is known for being stable and reliable and can be used in networks of all sizes. Redistribution between different routing protocols is a complex process, but in general, it allows for sharing information between networks that use different protocols. In the case of OSPF, redistribution occurs when routes from other protocols are injected into the OSPF network or vice versa. There are several benefits to redistributing routes in this way. First, it allows for greater flexibility in terms of routing. In particular, it can be used to connect disparate networks that would otherwise be unable to communicate with each other. Second, redistribution can improve network performance by allowing for more efficient routing of traffic. And finally, it can provide redundancy if one routing protocol fails or is unavailable. However, there are also some challenges associated with redistribution. In particular, it can lead to routing loops if not correctly configured. Additionally, it can add complexity to the network and make it more difficult to troubleshoot problems. For these reasons, careful planning is required before implementing redistribution in an OSPF network. How to Redistribute OSPF into BGP? One way to redistribute OSPF into BGP is using the redistributing OSPF command. This command will instruct the router to send a copy of the OSPF routing table to the BGP process. The router will then add the OSPF routes to the BGP routing table. How to Redistribute BGP into OSPF? There are several ways to redistribute BGP into OSPF, but the most common method is to use a route map. A route map is a set of instructions that tells a router how to handle the traffic that matches specific criteria. Creating a route map and applying it to BGP allows you to control which routes are redistributed into OSPF. You may like this post: BGP vs OSPF How to Redistribute OSPF into EIGRP? The process of redistributing routes from EIGRP into OSPF is relatively straightforward. First, you will need to edit the EIGRP configuration file and specify which routes you want to redistribute into OSPF. Next, you will need to edit the OSPF configuration file and add a rule that tells OSPF to accept routes from EIGRP. Finally, you will need to restart both the EIGRP and OSPF services for the changes to take effect. Following these steps can easily redistribute routes between these two protocols. How to Redistribute EIGRP into OSPF? One way is to use the redistribute command. This command can be used with several different routing protocols, including EIGRP and OSPF. When entering the redistribute command, you must specify the process ID for both EIGRP and OSPF. Another way to redistribute EIGRP into OSPF is to use route maps. Route maps can control which routes are redistributed and how they are redistributed. You will need to create a route map and then apply it to the redistribution process. Finally, you can use distribution lists to control which routes are redistributed. Distribute lists can be applied to both outgoing and incoming routes. You may like this post: EIGRP vs OSPF Final Words OSPF redistribution can be complex, but understanding the basics can make things easier for you.You can find more information about OSPF on CCIE Enterprise Infrastructure Course also.We hope this article has helped you understand the concept of OSPF redistribution.

Published - Sun, 09 Oct 2022

Created by - Orhan Ergun

OSPF Protocol Basic Overview

What is OSPF Language-wise it stands for Open Shortest Path First, and Family wise it belongs to the Link-State Interior Gateway Dynamic Routing Protocols. Done with the CV yet?, OSPF is an open standard internal routing protocol that is supported across all the different vendors manufacturing networking platforms. In this article, we will review the basics and specs of this protocol, and see its own unique features. OSPF Neighbor States As a start, the OSPF routing protocol uses a multicast hello message that is destined to the OSPF Multicast address of 244.0.0.5 seeking any possible other OSPF routers in the area. This message keeps repeating every 10 seconds by default, and that will be out of the interfaces that announced an OSPF configuration, which depends on how you configured it + the vendor-specific configuration template. Upon receiving a multicast hello message from another router we already sent it a hello message earlier, and that should be within the dead timer of 40 seconds maximum (by default). An OSPF neighbor process will start by: Init: at the moment of confirmation that a bidirectional multicast hello has initiated 2-Way: communication from the 2 parts has successfully occurred ExStart: OSPF router-id gets exchanged and database information begins to be shared Exchange: link states bidirectional communication and exchange Loading: final synchronization of LSA's Full: settlement and official neighboring announcement OSPF Routing Protocol Before starting routing, OSPF understands its neighboring environment by drawing a shortest-path tree SPT to those neighbors that it established a neighboring state with them earlier, based on the Dijkstra's Algorithm. Having the tree will allow the OSPF router to know how to reach each neighbor in the best way, and that will depend on the OSPF metric calculated per neighbor. named as the "Cost". OSPF at Rest With no triggers or events, OSPF routers will be calm, with no need to exchange any routes or LSA's, leaving the databases named LSDB's as steady, identical between routers, and containing the same types and amounts of LSA's. Only the OSPF hello message will be forever bidirectionally exchanged to maintain the neighbor state.

Published - Wed, 20 Apr 2022

Created by - Orhan Ergun

OSPF Configuration - A sample template on multi-vendor routers

There are commons and differences to the time when it comes to configuring an OSPF routing protocol on a router you manage, based on the router's manufacturer. We will take a look at the basic sample of configuring OSPF on Cisco IOS-XE and Juniper's JunOS operation systems. OSPF on Cisco IOS-XE With ios-xe we start configuring OSPF by mentioning the numerical value of the: OSPF Process ID And what that does mean is just a number to isolate some hierarchical designs of the OSPF process on the router of cisco. Does it have to be matched on both the peering ends?, the answer is NO Does it affect some priorities in some OSPF election processes?, the answer is also NO Is it that mandatory?, well based on that "OS" it is, but it is not a general OSPF concept? As it is missing with the other vendors!! That makes the first line of configuration look like this:         OERouter1(config)#router OSPF [Process ID] i.e. "OERouter1(config)#router ospf 10 OSPF Network Advertisement The later step after getting into the hierarchical mode of OSPF, specifying the process ID as well, is to advertise the networks. These networks prefixes and prefix lengths will be announced to the adjacent neighbors inside the transported LSA's of the OSPF routing protocol. OERouter1(config-router)#network [network prefix] [network wild card mask] _____ i.e. "OERouter1(config-router)#network 10.10.10.0 0.0.0.255 _____ and that will be advertising a network with the prefix of 10.10.10.0 and the prefix length of 24 OSPF Area ID The real key here in OSPF configuration is the Area ID, the Area ID does the isolation, it does the creation of multiple databases LSDB, it generates the need and the role for the ABR Router, It has to be matched on both the ends of the peering OSPF routers, and there will be a database for every area. OERouter1(config-router)#network [network prefix] [network wild card mask] Area [Area ID] i.e. "OERouter(1config-router)#network 10.10.10.0 0.0.0.255 Area 0 That line had just advertised the network of 10.10.10.0/24 into the domain and database of Area 0 Any other participating router within the same area will receive some LSA's carrying the 10.10.10.0/24 network advertisement. OSPF on JunOS OS On the other end, the other router awaiting to peer with the Cisco IOS-XE router will be a router from Juniper Networks, Having the one unified intelligent JunOS OS installed on, Here, just like it is with many other vendors, there will be no "Process ID" Advertise a network and its Area ID under the umbrella of OSPF configuration hierarchy, and that is it. [edit] [email protected]#edit protocols [dynamic routing protocol] [email protected]#edit area [Area ID] i.e. [email protected]#edit protocols OSPF [email protected]#edit area 0.0.0.0 Areas with JunOS can be mentioned either as a normal numerical value [0] or as a 32-bit value [0.0.0.0] The classic of JunOS is to use the [0.0.0.0] form. After specifying the Area ID, and also making sure that the syntax started with "edit" We will log in another JunOS hierarchical mode, where we can advertise "Participating Interfaces" instead of "Networks" [email protected]#set interfaces [interface_ID.logical_unit] i.e [email protected]#set interfaces ge-0/0/0.0 or: [email protected]#set interfaces ge-0/0/0 unit 0 Now any network getting advertised within the interface ge-0/0/0 generally (unit 0) Will be advertised out of that interface as a network participating in OSPF Area 0, to the other side. Point of Argument Will the above samples of configuring 2 different platforms, running 2 different operating systems, Having 2 different ways of advertising a network out, and also one of them misses a mandatory statement based on the other aspect, Will all of that work!!! The answer is YES, OSPF is an open standard protocol, it is supported across multiple vendors, the slight differences in configuration samples are just some languages differentiations, But neighboring adjacency will come up and full Link-State Databases (LSDB's) will be established and fully synchronized between the routers using LSA's. A more unified method As we've seen earlier, with Cisco IOS-XE, the OSPF configuration was done by advertising a network, while in JunOS it was done by advertising an interface. That can have an alternative way on Cisco's IOS-XE, by also advertising an interface, BUT, from the interface hierarchical config. mode. OERouter1(config)#interface [interface ID] OERouter1(config-if)#ip ospf [Process ID] Area [Area ID] i.e. OERouter1(config)#interface gi 0/1 OERouter1(config-if)#ip ospf 10 area 0

Published - Wed, 20 Apr 2022

Created by - Orhan Ergun

OSPF FAQ - Frequently Asked Questions

In this post, some of the frequently asked OSPF questions will be answered. Some of the answers will be from a design point of view and we will try to provide enough justification for the answer. Questions are selected randomly, not based on the order of importance. How many routers should be placed in one OSPF area? We don't give any numerical number as an answer to this question. Depending on the number of routers, links, prefixes, and the topology of the network also depends on the hardware capabilities and the performance of the routers, the number change from Network to network. In some networks, you can place only a couple of hundreds, and in some networks, you can place thousands of Routers in a single OSPF Area. What command would you use to only see the OSPF routes in the routing table? On Cisco devices, sh ip route ospf is used to see only the OSPF routes in the routing table. What will an OSPF router prefer to use first as a router-id? The first preference for an OSPF router ID is an explicitly configured 32-bit address. This address is not included in the routing table and is not defined by the network command. If it is not configured manually, the highest loopback IP address is used. In which OSI model layer will you find the OSPF protocol? OSPF is an IP-based protocol. Not like IS-IS or BGP. IS-IS is Layer protocol and BGP runs on top of Layer 4, TCP protocol. OSPF is Layer 3, IP Based protocol based on OSI Layer. What is one reason to use the ip ospf priority command when the OSPF routing protocol is in use? In DR and BDR selection in OSPF, a priority command is used for the election process. A higher priority router is selected as a DR. If the purpose is not to allow one of the routers in the election process, then ip ospf priority command is used. With multiarea OSPF, which OSPF router type has all interfaces in the same area? In Multi-area OSPF, which is also commonly known as Hierarchical OSPF design, Internal routers have all interfaces in the same area. ABR Routers need to have more than one Area, and one of the OSPF Areas, has to be OSPF Area 0, OSPF Backbone Area. Why would you want to change the OSPF default reference bandwidth? By default, the reference bandwidth is 100 Mbps. However, if you have faster links in your network, such as gigabit Ethernet or higher speed, OSPF can't give these links a better cost than 1. So you should set the reference bandwidth to at least as high as the fastest link in your network. Overall you can manipulate the cost, so you can do better Traffic Engineering by using OSPF cost. What is the format of the router id on an OSPF-enabled router? OSPF router ID is a 32-bit number formatted like an IPv4 address and assigned in order to uniquely identify a router. What is a benefit of multiarea OSPF routing? Multi-Area OSPF routing is done for scalability purposes. When routers are in place in different OSPF Areas, the purpose is to be able to send only summary routes or default route into the OSPF Non-Bachone Areas. Multiarea OSPF Routing is known as Hierarchical OSPF Routing and it is done to grow a number of routers and the prefixes in the OSPF network. What function is performed by the OSPF designated router? OSPF Designated Router also provides scalability. When it is used, routers don't have a full-mesh adjacency with each other in OSPF networks. Thus it reduces the number of control plane exchanges and LSA advertisements. Reducing flooding in case of newly added networks or in case of failure allows scalability. If there is a p2p network, we should avoid having OSPF DR. Which command will provide information specific to ospfv3 routes in the routing table? show ipv6 route ospf command provides information specific to ospfv3 routes only. Which command is used to display the collection of OSPF link states? show ip ospf database provides all the entries in the OSPF Link state database. What is a characteristic of a single-area OSPF network? Single Area OSPF network is by default placing routers in a single OSPF Area. It can be OSPF Backbone Area, which is OSPF Area 0. It is the most common deployment model. Or, if all the routers are placed in an OSPF Non-backbone area, which is any number other than Area 0, it is also called Single Area OSPF Routing design. Single-Area OSPF is known as a Flat OSPF network as well. What does an OSPF area contain? The OSPF area contains OSPF internal routers. Their connections, which mean links, and through these links, OSPF neighborship allows OSPF Routers to exchange IP prefixes. In a given OSPF Area, every router has the same Link state database. What command will display all connected ospfv2 routers? With show ip ospf neighbor command you can view the connected OSPFv2 routes. How to configure OSPF on the Cisco router? To enable OSPF on a Cisco router and advertise interfaces, the following tasks are required: Use the command router ospf process ID to start OSPF. Use the network command to enable the interfaces. Identify OSPF area assignments. (Optional) Assign the router ID. Which type of OSPF router will generate type 3 lsas? OSPF Type3 LSA is generated by the OSPF ABR to summarize OSPF Type 1 and OSPF Type2 LSA. Because between the OSPF Areas, Type 1 and Type 2 LSAs cannot be sent, Type 3 LSA is generated by the ABR to teach a given OSPF Area prefixes to another. What is the easiest and preferred method of manipulating OSPF route costs? OSPF uses cost to calculate the metric, based on the bandwidth of the link. Higher bandwidth means lower cost, and it is preferred over higher cost. So increasing bandwidth is one way to influence/manipulate the path in OSPF. What does the Cisco IOS use to calculate the OSPF cost to a destination network? Cisco and many other vendor Routers use Bandwidth to calculate OSPF cost to a destination network. Although cost can be manipulated manually and manual cost can be assigned based on other criteria such as delay/latency, fiber route mile, monetary cost, and so on, many networks in real-life OSPF design, keep the default cost parameter, which is bandwidth. In OSPF, hellos are sent to what IP address? OSPF neighbors are dynamically discovered by sending Hello packets out to each OSPF-enabled interface on a router. Hello packets are sent to the multicast IP address of 224.0.0.5. Which command can be used to verify the contents of the lsdb in an OSPF area? show ip ospf database is used to verify all the contents of the OSPF link-state database. We have two different databases in OSPF. One of them is LSDB, a link-state database and another is TED, a Traffic Engineering Database. Which type of OSPF LSA is generated by an ASBR and includes external routes? Type5 LSA is generated in OSPF by the ASBR and sent into the network. Single-Area OSPF and Multi-Area OSPF networks Type5 LSA is sent everywhere. Except, if the Area is Stub, Totally Stub, NSSA, or Totally NSSA, then Type 5 LSAs are not allowed into those OSPF Area Types. What are two reasons for creating an OSPF network with multiple areas? The main reason we create Multiple Areas in OSPF is Scalability. Scalability means allowing for growth. So, the number of Routers, links, and prefixes, in time, can grow and our network design shouldn't stop growing. When Multi-area OSPF is designed, into the Non-backbone areas topology information is not sent, thus it provides more stability in those areas. Also, convergence time gets faster and troubleshooting becomes easier in Multi-area network design. What default length is used for the OSPF dead interval? The default values are 10 seconds for the hello time, and 40 seconds for the dead time. The usual rule of thumb with OSPF is to keep the dead time value four times the hello interval. If OSPF fast convergence is the requirement, then these values can be reduced to provide fast failure detection. BFD is another method for fast failure detection. What are the enhancements that ospfv3 supports over ospfv2? In OSPFv3, similar to IS-IS protocol, reachability information and topology information are separated. So. when we add a new loopback interface (not topology change), in OSPFv2, it triggers full-SPF calculation, which is a resource-intensive task. Also, OSPFv3 supports both IPv6 and IPv4, but OSPFv2 only supports IPv4.

Published - Mon, 04 Apr 2022