To help illustrate better how the ospf messages are used, its worth taking a quick look at the format used for each of these messages. 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. Aug 30, 2011 strangely when i studied for my ccna, my instructor always used to tell me how multiarea ospf in ccnp was the hardest thing to grasp of all the material. Ospf continued minimises routing protocol traffic low bandwidth requirements supports different types of areas route summarisation and authentication ciscos implementation is fully compliant with the specification ospf v2. How ospf propagates external routes into multiple areas. We also saw the most common lsa packets found in ospf networks. Link state routing protocols advertise the state of their links. Ospf lsa types explained 7 ospf lsa types tutorial certiology. In this topology we have three areas 0, 1 and 2 so we can see the first three lsa types. Ospf adjacency process goes through the seven states. Summary lsa ip network 3 which means it was generated by an abr ospf router. An ospf network can be divided into subdomains called areas. The format of the common ospf header is shown below.
If you are preparing for the ccnp route exam, you should have a good understanding of ospf area types and the reasons for creating an ospf network with multiple areas. Type 7 lsas used to describe external lsa for one specific ospf area type 32. Rs coming up soon cisco live 2015 i figured this would be a good time to back over some basics, and when. With its fast convergence and scalability, ospf is well suited for multivendor. Generated by abrs, this type os lsa contain routes to asbrs.
The linkstate advertisement lsa is a basic communcation means of the ospf routing protocol. Also, like the type 1 lsa, these advertisements stay within the area. When building out an ospf network you must take into consideration of the internet network types. These lsa types are generated by the dr designated router and one type2 lsa is generated for every network with two or more ospf neighbors. Ospf lsa types purpose and function of every ospf lsa. Router link lsa type 1 each router generates a type 1 lsa that lists its active interfaces, ip addresses, neighbors and the. Most often used lsa types, router origin type, their function and areas affected. Feb 05, 20 top 20 ospf network engineer interview questions with answer asked in every interview duration. 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 protocol extensions, including the demand circuit extensions and the multicast extensions to ospf mospf an ospf faq. Ospf s interaction with frame relay will be explained in another section broadcast multiaccess indicates a topology where broadcast occurs. With the area types are being explained in this section this major rule has to be. Ospf state down, ospf state init, ospf state two ways, ospf state exstart, ospf state exchange, ospf state loading and ospf state full. Type 3 advertisements are generated by the abr area border router.
If you want to check lsa type 5 only, use the show ip ospf database external command. There are different types of linkstate advertisements lsas that would be used for open shortest path first ospf. It contains the router id rid, interfaces, ip information, and current interface state. Looking at the ospf packet captured with our network analyzer, we can now understand that the specific lsa was a type3 lsa ls type. Generally external routes are advertised by type 5 lsa but they are not allowed inside any stub area. It is one among the 2 link state routing protocols. In this part we explained basic terminology of ospf such as feature, advantage and disadvantage, autonomous system, area concept, abr, ir, link, state, lsa and lsdb with example. Ospf uses a lsdb link state database and fills this with lsas link state advertisement. Advantages of ospf areas, configuring and verifying basic ospf routing, ip ospf priority, linkstate data structures, loopback interfaces, notsostubby area nssa, osfp metric calculation, ospf, ospf adjacencies, ospf area structure, ospf lsa types, ospf lsdb, ospf. Consider the total cost up to the external destination e2.
Ospfs interaction with frame relay will be explained in another section broadcast multiaccess indicates a topology where broadcast occurs. Area id is the 32 bit area id assigned to an interface sending an ospf packet. A router within an area must maintain a topological database for the area to which it belongs. Lsa types explained complete understanding of lsa types is the cornerstone to understanding ospf areas and ospf area behaviors complete understanding of ospf area behaviors is the cornerstone of good ospf network design and traffic flow 2. In network basics,network planning, ospf on may 31, 2011 by carlosfvc tagged. Cisco router only supports lsa 1, 2, 3,4,5,7 and does not support other lsas. Ospf is very scalable and was designed specificly for larger networks. Ospf network types ospf s functionality is different across several different network topology types. 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. Instead of using 1 lsa packet ospf has many di erent types of lsas and in this tutorial im going to show all of them to you. Open shortest path first ospf is a widely used and supported routing protocol.
Please notice that we have not redistributed eigrp routes to ospf domain yet. Lsa type 1 router lsa packets are sent between routers within the same area of origin and do not leave the area. Type 1 lsa also known as router link advertisement rla, a type 1 lsa is sent by every router to other routers in its area. For many people it helps to visualize things in order to understand and remember. Ospf message formats page 1 of 7 ospf uses five different types of messages to communicate both linkstate and general information between routers within an autonomous system or area. It supports the ipv4, ipv6 networks, cidr and vlsm addressing models. Ospf lsa types explained with the help of network diagrams and examples. All the ospf routers have routerids in the form of x. Type 3 lsa filtering should be used at abrs and only routers.
The majority of the network setups use this protocol nowadays in favor of rip and sometimes eigrp due to it being a linkstate and open standard protocol. Dec 29, 2017 networking ospf overview of ospf lsa types the linkstate advertisement lsa is a basic communication means of the ospf routing protocol for the internet protocol ip. Its an interior gateway protocol igp meaning it been designed to be used within a single autonomous system. Networking ospf overview of ospf lsa types youtube. Our previous article explained the purpose of link state update lsu packets and examined the link state advertisement lsa information contained within lsu packets. Open shortest path first open shortest path first ospf is an openstandard link state routing protocol. Additions to the ospf neighbor structure the ospf neighbor structure is defined in section 10 of. Packet length is the total length of an ospf packet. On r7 use the show ip ospf database command to view the information related to ospf.
Router 1 should be a asbr which redistributes the static routes. Nov 04, 2014 open shortest path first ospf is a standard routing protocol thats been used the world over for many years. Pdf a practical approach to ospf link state advertisement lsa. Asbr summary lsa type 4 generated by abrs in ospf, and contains a route to any asbrs in the ospf system. On lsa arrivalon lsa arrival if router already has this version i. In this tutorial we will learn more about other lsa types types 1 to 5 and 7. May 14, 2015 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. Supported by practically every routing vendor, as well as the open source community, ospf is one of the few protocols in the it industry you can count on being available just about anywhere you might need it. Covering lsa1, lsa2, lsa3, lsa4, lsa5, lsa6, lsa7, lsa8, lsa8, lsa10.
Ospf not so stubby area type 7 to type 5 linkstate advertisement conversion. Considers only the cost of the outgoing interface to the external destination. Ospf being an open standard protocol works for each vendor router. Methods for debugging routing problems are explained, including a catalog of available debugging tools. Ospf network types ospfs functionality is different across several different network topology types. This document describes open shortest path first ospf areas and virtual links. You may expect questions such as which routes are allowed by a particular ospf area or when will a router in an ospf nonbackbone area receive a default route from the abr.
An area is a logical collection of ospf networks, routers, and links that have the same area identification. Ospf lsa types explained ospf uses a lsdb link state database and lls this with lsas link state advertisement. Pdf this report contains indepth information on ospf link state advertisement and network simulations on gns3 find, read and cite all the. Lsa type 6 multicast lsa this type of lsa is used for multicast applications. In an opaquecapable router, the following items are added to the ospf neighbor structure. When a link state router begins operating on a network link, information associated with that logical network is added to its local link state database lsdb. In this article well be diving deeper to analyse all eleven ospf lsa types using network network diagrams and examples to help understand when each lsa type is. In this article we will see how to configure ospf step by step.
Jun 28, 2017 it is time to take a look to configuring ospf open shortest path first with an ospf configuration example. This includes the common ip prefix that they work on as well. The following sample configuration documents fall under the multiple area and types of areas category. For example, you will learn why its important that there be an area 0 and what the consequences of traffic flow are if there is not an area 0. This article contains list of ospf lsa types with a short description. Lsa type 7 nssa external lsa type 7 lsa allow injection of external routes throug notsostubbyareas nssa. Note that type 1 lsas are flooded only across their own area. Ospf lsa types explained ospf uses a lsdb link state database and fills this with lsas link state advertisement. In the ospf, there are 5 different types of packets. Ip multicast and multicast routing are also discussed. This is advertised by the dr in an ospf network and describes all of the neighbors in the area. In this lesson ill explain the basics of ospf to you and you will learn how and why it works. Lsas build up the ospf link state database lsdb, and they are exchanged between ospf enabled nodes.
There are multiple ospf network types that can be configured to directly affect the operation of ospf on a specific interface. There are five types of ospf linkstate packets lsps. In our example, we will examine the figure below deeply. Jul 07, 2014 ospf is a widely used protocol in campus, data center and even in service provider environments. So far eigrp has been much more unpredictable and unintuitive for me with all those metrics and feasibility conditions and secondhand routing information. Perhaps it is the widely used interior gateway protocol in a large enterprise. An ospf router uses lsa type 1 packets to describe its own interfaces but also carries information about its neighbors to adjacent routers in the same area. This lab will discuss and demonstrate the configuration and verification of the different ospf network types. It communicates the routers local routing topology to all other local routers in the same ospf area.