Lsa types in ospf with example

This post will explain the cisco ospf lsa types hopefully in an easy to understand format. For many people it helps to visualize things in order to understand and remember. For example, you will learn why its important that there be an area 0 and what the consequences of traffic flow are if. Lsa type 1 these are also known as router lsas, every router participating in ospf will generate one of these, and type 1 lsas are. The example below shows two lsa s, both originated by the same router router id 192. In the following example, the output for the show ip ospf and show ip ospf database nssa commands shows an open shortest path first notsostubby area ospf nssa area where rfc 3101 is disabled, rfc 1587 is active, and an nssa area border router abr device is configured as a forced nssa lsa translator. Now it is time to go deep and combine virtual link, lsa types and etc. Ospf areas and lsa types this lesson explains and diagrams the concept of areas, how and why they are created, and how they impact the flow of traffic between routing devices. In this tutorial we will learn more about other lsa types types 1 to 5 and 7. Ospfs interaction with frame relay will be explained in another section broadcast multiaccess indicates a topology where broadcast occurs. Ospf uses a lsdb link state database and fills this with lsas link state advertisement. All routing devices in an area run this algorithm in parallel, storing the results in their individual topological databases. Type 1 router lsa the router announces its presence and lists the links to other routers or networks in the same area, together with the metrics.

Translated into an as external lsa type 5 by the abr at the nssa border. Asbrs run both ospf and another routing protocol, such as rip or bgp. Looking at the ospf packet captured with our network analyzer, we can now understand that the specific lsa was a type3 lsa ls type. Perhaps it is the widely used interior gateway protocol in a large enterprise. I hope you enjoyed this recap of the very important lsa types we have in ospf. All lsas regardless of type have an lsa header, which identifies important pieces of information about the lsa. Opaque lsa types used for applicationspecific purposes ospf lsa types and area types one of the reasons that you should master the different lsa types is the fact that it can help you fully understand the potential importance of a multiarea design, especially one that might include special areas. Router lsa type 1 network lsa type 2 abr summary lsa type 3 asbr summary lsa type 4 asbr externel lsa type 5 group summary type 6.

It communicates the routers local routing topology to all other. Ospf is a link state routing protocol that updates the routing table only when network changes occur, rather than at a predefined interval. The flooding is reliable, ensuring all routers have the same collection of lsas. Ospf lsa types cisco for ipv4 explained rogers ccie blog. Verifying and monitoring ospf configuration techlibrary. Master the ospf lsa types anthony sequeiras blog home. There are many specific area types that are used with ospf and these area types has specific characteristics. Remember, this command shows you only the lsa headers and with lsa1 and lsa4 in particular, they contain no addressing information. Distance vector routing algorithm with example iit lecture series duration. By default, the router id is typically the lowestnumbered ip address or the lowestnumbered userconfigured loopback interface configured on the device. In this article we will make an example for advanced ospf configuration. Instead of propagating external routes type 5 lsas into the area, the abr injects a type 3.

Each lsa has an aging timer which carries the linkstate age field. Summarylsa ip network 3 which means it was generated by an abr ospf router link state advertisement lsa packet structure within a link state update lsu. Ospf lsa type 4 in this example we have r1 that is redistributing information from the rip router into ospf. Ospf is designed for scalability, so some lsas are not flooded out on all interfaces, but only on those that belong to the appropriate area. Lets zoom in on the operation of how ospf keeps its linkstate database uptodate. There are eleven different lsa types and each of them has a special purpose. Discover how ospf areas and lsa types play crucial roles in helping. To try this at home, you can do a shorter version of the lab with just two routers. Type 5 external lsa these lsas contain information imported into ospf from other routing processes. Most often used lsa types, router origin type, their function and areas affected. Link state advertisements lsas are the buildinh blocks of ospf.

In this topology we have three areas 0, 1 and 2 so we can see the first three lsa types. In this next example, r2 and r3 share a common stub area. Router link lsa type 1 each router generates a type 1 lsa that lists its active interfaces, ip addresses, neighbors and the. Example of drs in an ospf area to learn the router priority on an interface, use the show ip ospf interface command and check the pri setting under ospf interface configuration. Descriptions of the ospf lsa types that are advertised in a cisco environment. You might have read that ospf uses a thing called a link state advertisement, or lsa for short. This article contains list of ospf lsa types with a short description. All lsas are flooded throughout the ospf routing domain. D explanation the output of the show ip ospf database is shown below. In example 326, notice two different type 1 lsas, or router link. By default each ospf lsa is only valid for 30 minutes. These lsa types are generated by the dr designated router and one type2 lsa is generated for every network with two or. Type1 router link advertisement this is a type1 lsa exchanged by the routers which belongs to a same area.

Displays lsa types per area, advertising router, link id subnet and age. For lsas type 4, the advertised asbr rid is in the link state id in the lsa header. For example, if you were writing an application and you decided you wanted to use ospf to transport the applications data but you did not want ospf to use this data for its own purposes. Verifying an ospf configuration, tracing ospf protocol traffic, example. Ospf uses the shortestpathfirst spf algorithm, also referred to as the dijkstra algorithm, to determine the route to each destination. The linkstate advertisement lsa is a basic communication means of the ospf routing. Please notice that we have not redistributed eigrp routes to ospf domain yet. Routing devices with interfaces to multiple areas run multiple copies of the. Covering lsa1, lsa2, lsa3, lsa4, lsa5, lsa6, lsa7, lsa8, lsa8, lsa10. This fact is confirmed by the output you have provided later yourself in the show ip ospf database router advrouter 2.

Ospf lsa types explained with the help of network diagrams and examples. This collection of lsas is called linkstate database lsdb. From the output above we can see lsa type 1 router link state and lsa type 3. So lots of good information in lsa1, think of these as a blueprint of the router, describing what is has and what it is doing. More then on ospf lsa type 5, external type 1 next blog post. Ospfv3 lsa types each lsa begins with a standard 20byte lsa header.

Such areas can be configured to block certain lsa types and become lightweight stub areas. For example, you have router one is plugged into the 10. It supports the ipv4, ipv6 networks, cidr and vlsm addressing models. The show ip ospf database command lists the lsas in that routers lsdb, with lsa type 1 lsas router lsas first, then type 2 network link states, continuing sequentially through the lsa types. All the ospf routers have routerids in the form of x. Opaque lsas are used to extend the capabilities of ospf, and to allow for transmission of arbitrary data that ospf does not necessarily need to care about. If the lsa expires then the router that created the lsa will resend the lsa and increase the sequence number.

We talked about ospf basics and made an ospf configuration for beginners on our course. Ospf supports variable length subnet masks vlsm and route summarization. Some of the lsa types are the main lsa types that are used in ospf operations often. Networking ospf overview of ospf lsa types youtube.

Well this is packet type or its communicated in packet type 4 called an linkstate update, or lsu. Did not understand difference between last type 4 and 5. It communicates the routers local routing topology to all other local routers in the same ospf area. Ospf summary mom, network engineer, juniper ambassador. Ospf has 11 lsa types from 1 to 11 but some of them are not used like type 6 multicast lsa, 8 used for bgp, 9, 10, 11 opaque lsas. Different types of lsa are created by each router throughout the network, to teach the rest of the network things like, for example, what links are attached to the router. It makes sense that this lsa has its own flooding scope, as its the one lsa thats flooded throughout the entire autonomous system, not just the area. For example, the type1 router lsa header is as follows. Lsa types there are different types of lsas exchanged depending upon the areas in which devices operating ospf reside. Ospf uses an hierarchical architecture and build ospf network with different areas. There are different types of linkstate advertisements lsas that would be used for open shortest path first ospf. Ospf network types ospfs functionality is different across several different network topology types.

Also note that the lsdb for area 3 should be identical on r33, r3, and r1. Used as generic lsas to allow for easy future extension of ospf. This blog will explain lsa types 1 through 5 as they are the most common lsa types encountered when first learning about ospf. Lsas build up the ospf link state database lsdb, and they are exchanged between ospf enabled nodes. The linkstate advertisement lsa is a basic communication means of the ospf routing protocol for the internet protocol ip. Very good explanation sir and what about lsa type 6 sir. Now remember the different packet types, there were five. Routers in ospf advertise information about the topology with what is called an lsa. Instead of using 1 lsa packet ospf has many different types of lsas and in this tutorial im going to show all of them to you. It is one among the 2 link state routing protocols. Ospf routers and links are grouped logically into areas that are identified by assigned numbers. For example, a type 6 lsa is used for multicast ospf and that technology never really caught on, allowing protocol independent multicast to win out. Configure the ip addresses as shown in this figure.