Ospf configuration s1720, s2700, s5700, and s6720 v200r011c10 configuration guide ip unicast routing huawei. Jun 21, 2010 if you want an asbr within the stub are you need to convert it into a nssa notsostubbyarea which uses type 7 external lsas. Ospf and route summarization inter area route summarization external route summarization stub areas redistributing routes into ospf e1 vs. In this update i will explore the different kinds of stub areas for ospf. Networks within this single as, however, can be divided into a number of areas.
Comparison of rip, ospf and eigrp routing protocols based on. Ospf inter area routes are advertised into the area, and the abr will inject a default route into a stub area. In this lesson i want to give you an overview of the different ospf stub areas. Lets have a look at the configuration for a stub area. Ospf commands area defaultcost p1r230 network protocols command reference, part 1 area defaultcost to specify a cost for the default su mmary route sent into a stub area, use the area defaultcost command in router configuration mode. Previously i explained the different ospf special area types called stub areas. Realtime ospf multiple choice questions and answers pdf. Stub area, asbr, and route redistribution topology example. Backbone area area 0 is the central of ospf network and all the other areas are connected to thsese backbone area. An ospf distribute list uses a route map or prefix list to filter specific routes from incoming ospf lsas. Configuring ospf areas techlibrary juniper networks. The book focuses on ospf open shortest path first, a common tcpip routing protocol that provides robust and efficient routing support in the most demanding internet environments. Specifies the ospf area to which the specified interface belongs. Now a days the majority of the network setups use this protocol.
If you use a stub area it will block all type 5 external lsas. The advertised prefix appears as an ospf internal route and is filtered at area borders with the ospf area ranges. R3, the abr, generates an inter area summary route and advertises this to the ospf backbone. Sep 12, 20 stub areas external lsas are stopped e1 and e2 routes default route is advertised into stub area by the abr all routers in stub area must be configured as stub totally stubby areas. Instead, external routes are replaced, by means of a type 3 lsa, with a single default route pointing to that areas abr. In lab 91 configuring basic ospf you learned about stub area s and their. A router within an area must maintain a topological database for the area to which it belongs. If area 1 is configured as a stub area, r2 which is acting as abr for area 1 will not allow lsa 4 and 5 to pass in to area 1. Configuring eigrp stub area networks free ccna workbook. Only regular areas are useful for isps other area types handle redistribution of other routing protocols into ospf isps dont redistribute anything into ospf.
In the topology shown, routers in area 7 do not need to know about all the external destinations. Jul 31, 2014 lets have a look at the configuration for a stub area. Using multiple areas in ospf reduces the router resource utilization because the routers. Sep 24, 2018 in order to become ospf neighbor following values must be match on both routers.
Ospf allows certain areas to be configured as stub areas. Use the area xx stub command in every router in the area to define an area as a stub area. In lab 91 configuring basic ospf you learned about stub areas and their purpose. Within area 1, routers r1, r2, and r3 exchange intra area routing information and maintain detailed topology for that area. Understanding ospf stub areas, totally stubby areas, and notsostubby areas.
A methodical and detailed description of the protocol is offered and ospf s role within the wider context of a tcpip network is demonstrated. The routing devices that participate in ospf routing perform. Figure 31 illustrates a basic multi area ospf network. Feb 08, 2016 my courses you can buy at lowest price. Route redistributionroutes learned via any ip routing protocol can be redistributed into any other ip routing. There are actually several different flavors of stub networks in ospf. Use the following commands on sanjose3, the abr, to configure area 2 as a totally stubby area. Ospf areas ospf areas group of contiguous hosts and networks per area topological database invisible outside the area reduction in routing traffic backbone area contiguous all other areas must be connected to the backbone virtual links area 1 area 4 area 0 backbone area area 2 area 3. Configure a stub network to advertise reachability to prefixes that are not running ospf. Ospf nssa not so stubby area ospf md5 authentication rotating key. To completely prevent summary lsas from being sent to the area, disable the summary lsas on each ospf router that is an abr for the area. Now that you know the basics necessary to fully understand ospf areas, we can discuss about different ospf area types.
Basic notes on ospf open shortest path first sysnet notes. Ospf will form neighbor relationships with adjacent routers in the same area. Make sure you understand the different ospf lsa types before you continue reading or it might be difficult to follow me. The filtered routes are not installed on the switch, but are still included in lsas sent by the switch. Stub area in ospf pdf this document describes open shortest path first ospf areas and virtual links. All routers in the area need to agree they are stub, so that they do not generate types of lsa not appropriate to a stub area.
Stub area, notsostubby area, totally stubby areas and totally nssa are other types of. This ospf lab is created in packet tracer and you will learn the ospf single area configuration from this lab. The abr does not allow type5 external routes to be propagated into the stub, replacing them with a default route. Basic ospf nssa totally stub a nssa totally stub is a type of stub area that can import autonomous system external routes and send them to other areas, but still cannot receive as external routes from other areas. U peruser static route o odr, p periodic downloaded static route gateway of. In addition, all ospf routing protocol exchanges are authenticated. In this article we will look at the stub area, totally stub, nssa not so stubby and. It allows the discovery of all ospf network devices in the network, without connecting to each of them or knowing all their ip addresses. Stub area s support multiple features that can reduce router resources and simplify configurations.
Ospf open shortest path first ospf is a standardized linkstate routing protocol, designed to scale efficiently to support larger networks. Ospf employs a hierarchical network design using areas. Stub area an area that has a single exit point and blocks type 57 lsa types and receives type 34 lsas with a default route 0. Each ospf area is named using a 32bit identifier which in most cases is written in the same dotteddecimal notation as an ip4 address. Ospf routes can also be exported into igrp, rip, and isis. Ospf adheres to the following link state characteristics. Ospf provides two levels of hierarchy through the use of areas. Or we can tell ospf to ignore the mtu size check with the command ip ospf mtuignore. Ospf external routes are not advertised into a stub area. Advertise default route default route lsas will be included in advertisements to the stub area along with a. Pdf a practical approach to ospf link state advertisement lsa.
This reduces the number of linkstate advertisements lsas and other ospf overhead traffic sent on the network, and it reduces the size of the topology database that each router must maintain. Figure 1 shows an autonomous system as across which many external routes are advertised. Link state advertisements lsa are accepted from other areas. Areas 1 and 2 are connected to area 0, the ospf backbone.
Stub areas and tsas apply only when the device is configured as an area border router abr for the area. This is a basic labs regarding ospf single area configure related to ccna or icnd12 exam. In 2008 free ccna workbook originally started as a sharable pdf but. What is the difference between a stub area, a totally stubby area, and a notsostubby area. Normal stub area from area 1s viewpoint summary networks from other areas injected default network injected into the area represents external links default path to closest area border router define all routers in the area as stub area x stub command asbr external networks 1. In ospf, a single autonomous system as can be divided into smaller groups called areas.
Instead r2 will inject a default route to area 1 which can be used by r1 to send packets to external networks. Refer to the ospf database explanation guide in order to learn more about the ospf database. This means you cannot have an asbr within the stub are because those are blocked. This way you can have external routing information within the stub area.
The totally stub types will do the exact same thing but they also block type 3 summary lsas in the area. An area is a logical collection of ospf networks, routers, and links that have the same area identification. E2 external routes redistributing ospf into other protocols use of a valid metric vlsm mutual redistribution injecting defaults into ospf ospf design tips number of routers per area number of neighbors. An ospf router instance can have one distribute list configured. Instead of advertising the distance to connected networks, ospf advertises the status of directly connected links using linkstate advertisements lsas. Ospf allows 5 different area types, which provides flexibility, fast convergence and scalability. An ospf area is a logical segment or a subdomain containing networks, routers and links sharing the same area id. Dec 09, 2011 a stub area in ospf is an area that will not learn external routes. In order to ensure consistent configuration of stub areas, all routers interfacing to such an area must have the ebit clear in their hello packets see sections 9. Stub areas external lsas are stopped e1 and e2 routes default route is advertised into stub area by the abr all routers in stub area must be configured as stub totally stubby areas. This lab will discuss and demonstrate the configuration and verification of ospf stub areas. Nov 06, 20 stub area an area that has a single exit point and blocks type 57 lsa types and receives type 34 lsas with a default route 0. Configuring the stub area, asbr, and route redistribution.
Now, what is this all about and why would you want to use something called a stub anyway. In following figure there are the three routers with. In the picture above we have 2 areasarea 0 and area 1. Configures an eigrp router as a stub router that will only advertise redistributed routes. Area 0 connected to other sections with abr area border router to exchange linkstate. Pdf this report contains indepth information on ospf link state. The user must provide the ip and snmp community string of a single ospf device in the network for example, a device in the core and the script searches for all other ospf routers. Area 0 can either function alone or act as the ospf backbone for a larger number of areas. You can configure area parameters only after enabling the ospf process. 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. Stub areas are not capable of importing routes external to ospf.
Ospf is an open standard protocol, you learn more why we use ospf and ospf quiz from here. In the next series of lessons i will show you the configuration of each ospf stub type. A stub area is an area into which no type 5 lsas are flooded. Therefore we need to adjust the mtu size on one of the router so that they are the same. Type 7 lsa used in stub areas in place of a type 5 lsa. An ospf network can be divided into subdomains called areas. Information exchange between routers in an area in ospf 2. Area cannot be a stub as it contains a virtual link theres our answer. Regular nonbackbone areas can have several subtypes. It is similar to standard area but it is build as area 0. Chapter routing protocols rip, ospf, and bgp pdf created with fineprint pdffactory pro trial version. Ospf is a widely used protocol in service provider environments. The next slides describing the different area types are provided for information only 38. Nssa totally stub is an extension of the stub area.
This chapter describes the implementation and application scenarios for ospf, as well as how to configure and troubleshoot ospf. If this option on a stub area area border router abr interface is disabled, the ospf area will behave as a totally stubby area tsa and the abr will not propagate any summary lsas. Default route is advertised into stub area by the abr. If external routes make up a significant portion of a topology database, you can suppress the advertisements in areas that do not have links outside the network. Route redistributionroutes learned via any ip routing protocol can be redistributed into any other ip routing protocol. Ospf networks in an autonomous system as are administratively grouped into areas. In this video we explore how stub and totally stub areas stub nosummary work, what ospf lsa they filter and how ospf provide connectivity to the routes that are lost with this lsa filtering. Advancing from last weeks discussion on ospf network types, todays topic is a source of considerable confusion for many people new to ospf. This document describes open shortest path first ospf areas and virtual links. This type of stub can be used in conjecture with the other stub types excluding receiveonly. For us to proceed with this task, lets remove the previous virtuallink configuration and configure area 26 as stub. Let me sum up some of the differences between the stub areas which will help you to beat these ospf labs.
All routers in the stub area must have the stub flag configured. In an autonomous, there is a backbone called area 0 which is the pivot of this autonomous. Apr 07, 2017 there are actually several different flavors of stub networks in ospf. At the intradomain level, this means that ospf can import routes learned via igrp, rip, and isis. We will observe independently the behavior of each of them and their implications. A totally stubby area is an area into which no type 3, 4, or 5 lsas are flooded, with the exception of type 3 lsas to advertise a default route. If youd like to learn more about the different types of lsa, wikipedia has a very good entry on them. A stub area in ospf is an area that will not learn external routes. Only the abrs also need to be configured for a default route injection. Each area within an as operates like an independent network and has a unique 32bit area id, which functions similar to a network address.
1048 1085 446 514 367 1239 779 1343 142 682 1400 773 620 933 483 1362 962 334 1388 1033 798 69 337 32 903 295 1018 1360 98 576 1270 1346 1077 668 971 385 1223 846