Given the complexity and scalability of ospf, different lsa types are used to keep the ospf database updated. This lab will discuss and demonstrate the configuration and verification of the different ospf network types. Open developed by ietf igp working group, rfc2328 spf each router floods linkstate information through its neighbors to other routers based on the flooded linkstate information, each router maintains a complete linkstate database based on the linkstate. Type 7 used in stub areas in place of a type 5 lsa. The difference between these two route type is explained before in nssa, summary lsa type 3 is accepted like stub area.
For example, if some vehicles enter a target area they will. Backbone area area 0 backbone area area 0 is the central of ospf network and all the other areas are connected to thsese backbone area. Configure ospf so there are two summaries for the loopback interfaces of router sam. Out of the various lsas, the first five are most relevant to the limited ospf discussion covered in this. Advancing from last weeks discussion on ospf network types, todays topic is a source of considerable confusion for many people new to ospf. There are different types of link state packets, those are what you normally see in an ospf database appendix a. Ospf open shortest path first link state or spf technology developed by ospf working group of ietf rfc 1247. The format of common ospf header is version 2 1byte type it specifies the type of ospf packet. Ospf allows 5 different area types, which provides flexibility, fast convergence and scalability. 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. Ospf allows for a logical definition of networks where routers can be divided into areas. Open shortest path first ospf is the first linkstate protocol that you will learn about. Ospf defines five different message types, for various types of communication.
Network links nl are generated by a dr of a particular segment. All ospf packets share a common ospf header of 24bytes. For many people it helps to visualize things in order to understand and remember. Bgp pdf created with fineprint pdffactory pro trial version. Ospf is a widely used protocol in service provider environments. It is responsible for distributing routing information between areas that are not backbone area types. You can see that r1 has learned about the network 192.
The linkstate id of the type 1 lsa is the originating router id. As a result of this deployment and the evolution of networking technology, ospf has been extended to support many options. In todays post, we will talk about the different ways we can perform filtering in ospf. The manufacturer reserves the right to modify the product and manual for the purpose of. These two routers are described later in this chapter. You will learn all the secrets about ospf, metrics, authentication, area types and more. 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 to them. Ospf relies on several types of link state advertisements lsas to communicate link state information between neighbors.
Ospf will form neighbor relationships with adjacent routers in the same area. Open shortest path first ospf is a routing protocol for internet protocol ip networks. 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. 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. 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. Recall that a large ospf domain is typically broken into separate areas to restrict the propagation of routes and reduce the amount of resources required by each router to maintain its link state database. In 2008 free ccna workbook originally started as a sharable pdf but. 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. All routes marked with the character o are ospf routes. Ospf network types ospf s functionality is different across several different network topology types. So if thinking in terms of the ospf backbone the abr is the responsible one that only generates type 4 lsas. There are multiple ospf network types that can be configured to directly affect the operation of ospf on a specific interface. Ospf open shortest path first ospf is a standardized linkstate routing protocol, designed to scale efficiently to support larger networks. Below is an example of a sticker with a huawei modem the modem symbol is.
Nonbroadcast network types require additional configuration to allow for both broadcast and multicast support. On such networks, ospf elects a designated router dr andor a backup designated router bdr. Ospf basics and features link state routing protocol. Ospf open shortest path first linkstate based routing protocol. Lsas build up the ospf link state database lsdb, and they are exchanged between ospf enabled nodes. All the ospf routers have routerids in the form of x. In this article we will examine ospf lsa types and i think it will help for the people who prepare for ccnp routing exam. In this video, we are going to see about, ospf lsa types explained tamil you can also look into my blog. This tutorial explains how to configure ospf routing protocol step by step with practical example in packet tracer. Beside, if a defaultinformation originate command is used in abr, defaultroute is also accepted. Whether the other types of lsas are advertised within an area depends on the area type, and there are many.
As an example of type 1 external metric processing, suppose that the routers rt7. Before and during this detailed check, you can use the below diagram to remember ospf areas and their specific advertisement acceptance rules. Standart area backbone area area 0 stub area totally stubby area nssa totally nssa. Router lsa type 1 contains a list of all links local to the router, and the status and cost of those links.
With its fast convergence and scalability, ospf is well suited for multivendor. Ospf and bgp for both the ipv4 and ipv6 protocol versions. Lsa types 1 and 2 are found in all areas, and are never flooded outside of an area. It is similar to standard area but it is build as area 0. Now a days the majority of the network setups use this protocol. The type 4 lsa does represent the external routes in a matter of speaking but its representing the path to the asbr only that contains the external routes type 7.
Ospf p art 1 protocol header type attributes algorithm metric linkstate dijkstra cost bandwidth ad standard protocols transport 110 rfc 2328, 2740 ip ip89 router types internal router all interfaces reside within the same area backbone router a router with an interface in area 0 the backbone area border router abr connects two or. If you redistribute routes into ospf from other routing protocols or from static, it causes these routes to become ospf. Ospf lsa types explained ospf uses a lsdb link state database and fills this with lsas link state advertisement. 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. This report discusses about the ospf protocol, its. As a network engineer in the field working with ospf you must know the differences in the ospf network types and which types are compatible with one another. 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. The table below lists the full ospf lsa types with a brief description for each lsa in the right part.
Type 1 lsas are generated by all routers in ospf, and. This header allows the receiving router to validate and process the packets. Each of lsa types advertises different information in ospf. Ospf neighbor discovery process ospf packet types and format ospf network topology. Monitoring and maintaining ospf abr type 3 lsa filtering 114. Ospf adheres to the following link state characteristics. Ospf is a widely used protocol in campus, data center and even in service provider environments. Although basic ospf configuration can be very simple, ospf provides many extra features that can get really complex. In this topology we have three areas 0, 1 and 2 so we can see the first three lsa types. Introduction over the last several years, the ospf routing protocol has been widely deployed throughout the internet. 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.
It supports the ipv4, ipv6 networks, cidr and vlsm addressing models. The routes that is related to type 7 lsas, will be like n1 and n2 routes in the routing table. There are different types of linkstate advertisements lsas that would be used for open shortest path first ospf. Deep understanding of ospf link state advertisments lsas is crucial to understand ospf behavior. 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. Master thesis jon larizgoitia university of twente. This paper examines how ospf works and how it can be used to design and build large and. This article contains list of ospf lsa types with a short description. The most common example of a nonbroadcast network type is frame relay. Ospf uses a lsdb link state database and fills this with lsas link state advertisement. Type 1 lsas are flooded across their own area only. It accepts, lsa type 1, type 2, type 3, type 4 and type 5 lsas.
In the case of stud area, routing in the area is entirely on the basis of a default route. Totally ospf has 11 types of lsa but in this article, we are going to analyze three of the most common lsas. External routes fall under two categories, external type 1 o e1 and external type 2 o e2. There are five different configurable ospf network types on a cisco router, broadcast, nonbroadcast, pointtopoint, pointtomultipoint and pointtomultipoint nonbroadcast. Ospf employs a hierarchical network design using areas.
Ospf s interaction with frame relay will be explained in another section broadcast multiaccess indicates a topology where broadcast occurs. Please notice that we have not redistributed eigrp routes to ospf domain yet. Five types of ospf routing protocol packets hello packet type 1. Rip and ospf o exterior routing n routing between autonomous systems n only one exterior routing protocol is usually used for exterior routing n examples. On r7 use the show ip ospf database command to view the information related to ospf. For example, here is the output of the command on r1. Ospf cost metric of an interface is an indication of the overhead required to send packets across a. The open shortest path first ospf protocol, defined in rfc 2328, is an interior gateway protocol used to distribute routing information within a single autonomous system.
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