This paper examines how ospf works and how it can be used to design and build large and. Router a should see routes for and be able to ping the loopback interface on router c and vice versa. Chapter 10 configuring ospf this chapter describes how to configure ospf on the hp procurve 9304m, 9308m, and 6308msx routing. Configure ospf router ids the ospf router id is used to uniquely identify the router in the ospf routing domain. Interarea route routes advertised from one area to another by an area border router. This allows you to configure the interface to send ospf traffic to its neighbor as unicast packets rather than multicast packets. A 32bit number assigned to each router running the ospf protocol. The version 2 of open shortest path first ospf defined in 1998 for. These types of routers have a single linkstate database because they belong to only one area. Backbone at least one ospf interface must belong to area 0 backbone area area border router. External route routes imported into ospf from other protocol or static routes r1 r2 r3 r5 r4 rd ra rc rb ir abrbr asbr to other as ir area 1.
Ospf gives the user freedom to assign cost metrics to a particular host router so that certain paths can be given preference. There are four types of ospf routers which are determined by a router s function andor location within an ospf area. This lsa type can not pass throught the abr area border router and can not go to the other areas. Different ospf network types with their examples are given below. Rfc 1586 was draftietfospfguidelinesfrn guidelines for running ospf over frame relay networks. 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. Ospf routers will only become neighbors if the following parameters within a hello packet are identical on each router. Pdf open shortest path first ospf routing protocol. Unlike other routing protocols, the ospf will not carry the data through the transport protocol such as tcp and udp. All ospf packets share a common ospf header of 24bytes.
A concrete understanding of how ospf routing works is fundamental for any small or large network. 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. Internal ir all ospf interfaces must belong to the same ospf area. This flow shows the message exchange that takes place when a new ospf router comes online. Place each interface on your router into the area specified by the diagram. Router external route routes imported into ospf from other protocol or static routes area 2 area 0 area 3 abr to other as asbr. Ospf router startup and link state update ospf open shortest path first is a routing protocol that is used as an interior gateway protocol in large enterprises. Instead of using the above four packets may i use only router lsa packets because.
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. Ospf configuration, the router sends a notification message to the console stating that a neighbor relationship with another ospf router has been established. A router that has ospf neighbor relationships with devices in multiple areas. Now a days the majority of the network setups use this protocol. The format of common ospf header is version 2 1byte type it specifies the type of ospf packet. Open shortest path first ospf is an active routing protocol used in internet protocol. A simulation of the ospf election protocol shows three results. The authentication type must be the same for all routers and access servers in an area. Ospf will first look at the type of path to make a decision and secondly look at the metric. Ospf open shortest path first is a popular linkstate routing protocol.
Well look at router 9 as our example to complete this. What is the difference between dd,lsrequest,lsupdate,lsack packets and router lsa 2. Routers will exchange pieces of information called lsas link state advertisement in order to build a complete topology database which we call the lsdb link state database. Hi, after reading about the ospf packet types i am having some doubts, 1. The nonbroadcast option configures the network type as a nonbroadcast connection. This protocol also incorporates support for a variable network subnet mask, which makes it easy for a network to be subdivided. How to configure basic ospf by brandon carroll in networking on july 26, 2017, 12. Hop count is the metric that rip uses and the hop limit limits the network size that rip can support. This command launches you into the ospf router level where you can assign areas and modify ospf global. Configuring basic ospf routing lab continued ospf objectives. The below chapter will cover about the ospf and its packet types. Since abrs are always connected to the backbone, they are always classified as backbone routers.
External route routes imported into ospf from other protocol or static routes. Open shortest path first ospf is the first linkstate protocol that you will learn about. The authentication password for all ospf routers on a network must be. Ospf uses the dijkstra shortest path first algorithm to determine the shortest path. Apart from being a linkstate protocol, it is also an open standard protocol. Comparison of rip, ospf and eigrp routing protocols based. Specifies network directly connected to the router network 172. Routers that act as gateways redistributionbetween ospf and other routing protocols igrp, eigrp, isis, rip. Ospf will form neighbor relationships with adjacent routers in the same area. Ospf employs a hierarchical network design using areas. Ospf with three routers the physical topology is as shown in fig 18.
Internal routers irs are routers whose directly connected networks all belong to the same ospf area. Both end routers must share a common area at least one end must reside in area 0 cannot traverse stub areas area types standard area default ospf area type stub area external link type 5 lsas are replaced with a default route totally stubby area type 3, 4, and 5 lsas are replaced with a default route not so stubby area nssa a stub area containing an asbr. There are five different configurable ospf network types on a cisco router, broadcast, nonbroadcast, pointtopoint, pointtomultipoint and pointtomultipoint nonbroadcast. An ospf network can be divided into subdomains called areas. All ospf packets will share the common ospf header of the 24 bytes.
A router has a separate ls database for each area to which. Each router has a unique role and set of defining characteristics within the hierarchy. Open shortest path first ospf operating inside a distinct autonomous system. That header allows receiving the router to validate as well as process the packets. Abrs gather topology information from their attached areas and distribute it to the backbone area. Advancing from last weeks discussion on ospf network types, todays topic is a source of considerable confusion for many people new to ospf. Ospf configuration s1720, s2700, s5700, and s6720 v200r011c10 configuration guide ip unicast routing huawei. Ospf open shortest path first ospf is a standardized linkstate routing protocol, designed to scale efficiently to support larger networks. Ospf is commonly used in large service provider networks or large financial institutions. 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. Five types of ospf routing protocol packets hello packet type 1 database description packet type 2. Since the router will not have detailed topology information of routers in other areas, this would greatly reduce the size of database.
Service type dependent the cost of the network depends on what service the packet needs. Backbone at least one ospf interface must belong to area 0 backbone area area border router abr at least one ospf interface must belong to area 0 backbone area and at least. Router is configured for ospf and assigned as 107 router ospf 107. The broadcast option configures the network type as a broadcast connection. This header allows the receiving router to validate and process the packets. Three typical types of routing protocol are chosen as the simulation samples. This is the default option for ethernet, ve and loopback interfaces. Ospf utilizes different types of ospf routers which are determined by the role and location of a router within an ospf domain. Router lsa type 1 list router neighbors and their costs. 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. Open shortest path first open shortest path first ospf is an openstandard link state routing protocol. There are different types of link state packets, those are what you normally see in an. The following sections provide general descriptions for the four types of ospf routers.
As you might have learned in ccna or ccnp, ospf will use cost as the metric to choose the shortest path for each destination, this is true but its not entirely correct. It is important that you are able to discern the different types of ospf routers and understand their features and functions. You may have realized that you cannot run eigrp in a. What this means is that you can run ospf in a network consisting of multivendor devices. You also can change the amount of memory allocated to various types of lsa entries. Understanding basic open shortest path first ospf routing principles not only applies to the ccnp certification but to all ciscobased certifications.
A list of link state advertisements is used in dealing with all ospf packet types. Abrs are attached to multiple ospf areas, so there can be multiple abrs within a network. It is one among the 2 link state routing protocols. Router use this number to identify themselves when generating updates. Rip routing information protocol is one of the oldest routing protocols still in service. It supports the ipv4, ipv6 networks, cidr and vlsm addressing models. 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. 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. A router within an area must maintain a topological database for the area to which it belongs. A router that has interfaces in multiple areas is called an area border router abr. Place loopback interfaces in whatever area makes the most sense. Ospf is a widely used protocol in service provider environments. Th is number uniquely identifies the router within an autonomous system.
There are four types of ospf routers which are determined by a routers function andor location within an ospf area. This chapter describes the implementation and application scenarios for ospf, as well as how to configure and troubleshoot ospf. In the following example, an open shortest path first ospf stub network is configured to include ospf area 0 and ospf area 1, using five devices. Beginning of all ospf packets is specified by standard header of 24 bytes. Perhaps it is the widely used interior gateway protocol in a large enterprise. Ospf adheres to the following link state characteristics. Link state routing protocols advertise the state of their links. A backbone router is a router that runs ospf and has at least one interface connected to the ospf backbone area. In this intermediate level tutorial, we introduce you to the different ospf area types. Two routers that have interfaces to a commo n network. Ospf is a classless protocol, and thus supports vlsms. Ospf router lsa type 1 router lsa type 1 is used for only internal routers in a standard area.
1149 1299 948 898 570 974 32 258 1432 839 179 190 175 1465 801 1544 414 839 905 573 1305 127 1402 1451 592 596 1441 397 1158 1438 473 102 400 642 912 400 832 162