Lsa types in ospf with example

The example below shows two lsa s, both originated by the same router router id 192. Building the linkstate database ospf implementation cisco. All ospf networks have at least one area with the default being area 0. For example, you have router one is plugged into the 10. By default, the router id is typically the lowestnumbered ip address or the lowestnumbered userconfigured loopback interface configured on the device. Covering lsa1, lsa2, lsa3, lsa4, lsa5, lsa6, lsa7, lsa8, lsa8, lsa10. If the lsa expires then the router that created the lsa will resend the lsa and increase the sequence number. In this article we will make an example for advanced ospf configuration. 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.

For example, ospfte has traffic engineering extensions to be used by rsvpte in multiprotocol label switching mpls. 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. Ospf uses an hierarchical architecture and build ospf network with different areas. This collection of lsas is called linkstate database lsdb. Most often used lsa types, router origin type, their function and areas affected. The flooding is reliable, ensuring all routers have the same collection of lsas. Ospf network types ospfs functionality is different across several different network topology types. Link state advertisements lsas are the buildinh blocks of ospf. To try this at home, you can do a shorter version of the lab with just two routers.

Lets zoom in on the operation of how ospf keeps its linkstate database uptodate. This blog will explain lsa types 1 through 5 as they are the most common lsa types encountered when first learning about ospf. 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. Ospf routers and links are grouped logically into areas that are identified by assigned numbers. Perhaps it is the widely used interior gateway protocol in a large enterprise. D explanation the output of the show ip ospf database is shown below. Now remember the different packet types, there were five. By default each ospf lsa is only valid for 30 minutes. 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. Ospf lsa type 4 in this example we have r1 that is redistributing information from the rip router into ospf. Ospf uses a lsdb link state database and fills this with lsas link state advertisement. Some of the lsa types are the main lsa types that are used in ospf operations often. Displays lsa types per area, advertising router, link id subnet and age.

Descriptions of the ospf lsa types that are advertised in a cisco environment. Instead of propagating external routes type 5 lsas into the area, the abr injects a type 3. 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. I hope you enjoyed this recap of the very important lsa types we have in ospf.

Each lsa has an aging timer which carries the linkstate age field. All routing devices in an area run this algorithm in parallel, storing the results in their individual topological databases. Ospf lsa types cisco for ipv4 explained rogers ccie blog. Verifying and monitoring ospf configuration techlibrary.

In this topology we have three areas 0, 1 and 2 so we can see the first three lsa types. These lsa types are generated by the dr designated router and one type2 lsa is generated for every network with two or. 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. This post will explain the cisco ospf lsa types hopefully in an easy to understand format. 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.

For example, the type1 router lsa header is as follows. You might have read that ospf uses a thing called a link state advertisement, or lsa for short. Asbrs run both ospf and another routing protocol, such as rip or bgp. 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. For lsas type 4, the advertised asbr rid is in the link state id in the lsa header. Type 5 external lsa these lsas contain information imported into ospf from other routing processes. For many people it helps to visualize things in order to understand and remember. Lsas build up the ospf link state database lsdb, and they are exchanged between ospf enabled nodes. 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.

All lsas are flooded throughout the ospf routing domain. Ospfv3 lsa types each lsa begins with a standard 20byte lsa header. Ospf is a link state routing protocol that updates the routing table only when network changes occur, rather than at a predefined interval. Remember, this command shows you only the lsa headers and with lsa1 and lsa4 in particular, they contain no addressing information. Ospf supports variable length subnet masks vlsm and route summarization. Distance vector routing algorithm with example iit lecture series duration. Ospf summary mom, network engineer, juniper ambassador.

Routing devices with interfaces to multiple areas run multiple copies of the. Ospf lsa types purpose and function of every ospf lsa. Type1 router link advertisement this is a type1 lsa exchanged by the routers which belongs to a same area. 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. In this next example, r2 and r3 share a common stub area.

All lsas regardless of type have an lsa header, which identifies important pieces of information about the lsa. For lsas type 3, the advertised prefix is in the link state id in the lsa header. 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. Master the ospf lsa types anthony sequeiras blog home. 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. In this tutorial we will learn more about other lsa types types 1 to 5 and 7. Verifying an ospf configuration, tracing ospf protocol traffic, example. This fact is confirmed by the output you have provided later yourself in the show ip ospf database router advrouter 2. The linkstate advertisement lsa is a basic communication means of the ospf routing. Routers in ospf advertise information about the topology with what is called an lsa. It supports the ipv4, ipv6 networks, cidr and vlsm addressing models.

There are eleven different lsa types and each of them has a special purpose. 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. Networking ospf overview of ospf lsa types youtube. Very good explanation sir and what about lsa type 6 sir. It is one among the 2 link state routing protocols. 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. In example 326, notice two different type 1 lsas, or router link. Please notice that we have not redistributed eigrp routes to ospf domain yet. Also note that the lsdb for area 3 should be identical on r33, r3, and r1.

On r7 use the show ip ospf database command to view the information related to ospf. Configure the ip addresses as shown in this figure. Ospfs interaction with frame relay will be explained in another section broadcast multiaccess indicates a topology where broadcast occurs. Ospf lsa types in cisco multiarea environment icnd2 200105. There are different types of linkstate advertisements lsas that would be used for open shortest path first ospf.

The linkstate advertisement lsa is a basic communication means of the ospf routing protocol for the internet protocol ip. Ospf lsa types explained with the help of network diagrams and examples. Discover how ospf areas and lsa types play crucial roles in helping. Well this is packet type or its communicated in packet type 4 called an linkstate update, or lsu. This article contains list of ospf lsa types with a short description. Lsa types there are different types of lsas exchanged depending upon the areas in which devices operating ospf reside. Now it is time to go deep and combine virtual link, lsa types and etc. There are many specific area types that are used with ospf and these area types has specific characteristics. Such areas can be configured to block certain lsa types and become lightweight stub areas. We talked about ospf basics and made an ospf configuration for beginners on our course. Looking at the ospf packet captured with our network analyzer, we can now understand that the specific lsa was a type3 lsa ls type. Used as generic lsas to allow for easy future extension of ospf. It communicates the routers local routing topology to all other.