Networking ospf overview of ospf lsa types youtube. 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. It supports the ipv4, ipv6 networks, cidr and vlsm addressing models. Beginning of all ospf packets is specified by standard header of 24 bytes.
On r7 use the show ip ospf database command to view the information related to ospf. The flooding is reliable, ensuring all routers have the same collection of lsas. When a link changes state, the device that detected the change creates a linkstate advertisement lsa concerning that link and sends to all neighboring devices using a special multicast address. Descriptions of the ospf lsa types that are advertised in a cisco environment. Most often used lsa types, router origin type, their function and areas affected.
Ospf s interaction with frame relay will be explained in another section broadcast multiaccess indicates a topology where broadcast occurs. Router lsa type 1 contains a list of all links local to the router, and the status and cost. Now a days the majority of the network setups use this protocol. 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 router lsa type 1 router lsa type 1 is used for only internal routers in a standard area. We use pim protocol independent multicast for multicast congurations. I would say that the ospf packet, can be one of the 5 types, and if its the lsu type, youve got your 11 different lsa types to choose from.
Type 7 lsas used to describe external lsa for one specific ospf area type 32. These lessons will teach you everything, we start with the basics and work our way through the most advanced ospf topics. All the ospf routers have routerids in the form of x. Prevention ospf areas should be defined as stub to prevent accidental redistribution of ebgp into ospf type 3 lsa filtering should be used at abrs and only routers loopbacks should be allowed to leak into other areas loopback should be in private address space to make lsa type 3. Using multiple areas in ospf reduces the router resource utilization because the routers.
There are four types of ospf routers which are determined by a routers function andor location within an ospf area. Hello is a handshake packet tells about the alive status of ospf interface. Flooding of this excess lsas would be chaotic itself for the network. Ospf provides two levels of hierarchy through the use of areas. D explanation the output of the show ip ospf database is shown below. 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. Ospf network types ospf s functionality is different across several different network topology types. Lsas type 1 are only sent among ospf routers in the same area so we see r5, r6 and r7 here which are in area 2 only. Type 6 multicast ospf lsa i lsa i can skip because its not being used. Hi, after reading about the ospf packet types i am having some doubts, 1. The link ids of type 2 lsa are the ip interface addresses of the drs. The ospf router summarizes the local database and the dbd packets carry a set of lsas belonging to the database.
Looking at the ospf packet captured with our network analyzer, we can now understand that the specific lsa was a type3 lsa ls type. Linkstate routing protocols generate routing updates only when a change occurs in the network topology. This includes the state of the router s interfaces and adjacencies. Ospf is a widely used protocol in service provider environments. 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. 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 will form neighbor relationships with adjacent routers in the same area. Instead of using the above four packets may i use only router lsa packets because it will send the update to all neighbors 3. Lsa type 1 router lsa packets are sent between routers within the same area of origin and do not leave the area. External routes fall under two categories, external type 1 o e1 and external type 2 o e2. 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 used and how they keep the ospf network updated.
Jun 24, 2008 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 linkstate advertisements lsas that would be used for open shortest path first ospf. So i decided to make a small cheatsheet with a small example configuration in my lab. 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. When a neighbor sees an lsa that is more recent than its own database copy, it requests this newer lsa from the neighbor. Type 3 lsa filtering should be used at abrs and only routers loopbacks should be allowed to. Rfc 1586 was draftietfospfguidelinesfrn guidelines for running ospf over frame relay networks. Ospf uses a lsdb link state database and fills this with lsas link state advertisement. This is advertised by the dr in an ospf network and describes all of the neighbors in the area. The lsa type 3 which shares internal routes and lsa type 5 that shares external routes flood through this area. Also removes lsa 3nssa allow external routes to be flooded to the area 0, using lsa type 7. 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. Describes the local state of the router or network. Ospf being an open standard protocol works for each vendor router.
Router lsa type 1 list router neighbors and their costs. Ospf uses link state advertisement lsa to build up link state database lsdb so understanding how lsa works is the key point to grasp how ospf operates. Generally external routes are advertised by type 5 lsa but they are not allowed inside any stub area. 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. Ospf gives the user freedom to assign cost metrics to a particular host router so that certain paths can be given preference. Ospf employs a hierarchical network design using areas. The basics of linkstate routing protocols and ospf. This includes the common ip prefix that they work on as well.
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. Ospfv3 lsa types each lsa begins with a standard 20byte lsa header. It is one among the 2 link state routing protocols. 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. Jan 08, 2016 ospf areas and area types ospf provides two levels of hierarchy through the use of areas. Type 7 lsa is generated by nssa asbr and is translated into type 5 lsa as it leaves the area by nssa abr, which. It communicates the routers local routing topology to all other local routers in the same ospf area. Ospf uses database descriptor dbd packets for this purpose. Cisco router only supports lsa 1, 2, 3,4,5,7 and does not support other lsas. Ospf relies on several types of link state advertisements lsas to communicate link state information between neighbors. This collection of lsas is called linkstate database lsdb. Adv router is the router that is advertising that information. Lsa type 1 and 2 are sent between routers within an area and thus help prepare the shortest path tree for an area. The collected link state advertisements of all routers and networks forms the protocols topological database.
In this topology we have three areas 0, 1 and 2 so we can see the first three lsa types. Consider the total cost up to the external destination e2. Instead of using 1 lsa packet ospf has many different types of lsas. Ospf uses an hierarchical architecture and build ospf network with different areas. They give information about every segment in our network outside of its area. 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 lsa has types depend on the type of router and has also sequence number.
Each link state advertisement is flooded throughout the routing domain. These are used when routing using multicast the modpf routing protocol these lsas are not supported by cisco routers lsa type 7 external lsa. From the output above we can see lsa type 1 router link state and lsa type 3 summary net link state. The next slides describing the different area types are provided for information only 38. Ospf open shortest path first ospf is a standardized linkstate routing protocol, designed to scale efficiently to support larger networks. Perhaps it is the widely used interior gateway protocol in a large enterprise.
It is important that you are able to discern the different types of ospf routers and understand their features and functions. Ospf cheat sheet 3 designated router dr backup dr bdr election there are two problems with multiaccess networks. Type 1 lsas are generated by all routers in ospf, and. Networking what are the different ospf packet types. Type 7 lsa is generated by nssa asbr and is translated into type 5 lsa as it leaves the area by nssa abr, which is then propagated throughout the network as type 5 lsa. Mar 22, 2011 ospf utilizes different types of ospf routers which are determined by the role and location of a router within an ospf domain. Lsa type 1 these are also known as router lsas, every router participating in. Also, like the type 1 lsa, these advertisements stay within the area. There are many specific area types that are used with ospf and these area types has specific characteristics. This type of lsa, can be found in any ospf area type.
This protocol also incorporates support for a variable network subnet mask, which makes it easy for a network to be subdivided. The link ids of type 1 lsa are the originating router ids. Like type 1 router lsa, also is created by every router in. Lsas build up the ospf link state database lsdb, and they are exchanged between ospf enabled nodes. Please notice that we have not redistributed eigrp routes to ospf domain yet. All the router ospf priorities are at the default and the router ids are shown with each router. 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. Type 1 lsas are generated by all routers in ospf, and are flooded to all other routers within the local area. 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. 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. Tottally means that removes lsa 3 and adds those routes to the default route. Ospf lsa types purpose and function of every ospf lsa. Type 5 external lsa these lsas contain information imported into ospf from other routing. If you redistribute routes into ospf from other routing protocols or from static, it causes these routes to become ospf.
Whats the difference between lsa and lsr, lsu, lsack in ospf. Only regular areas are useful for isps other area types handle redistribution of other routing protocols into ospf isps dont redistribute anything into ospf. All lsas are flooded throughout the ospf routing domain. Link state advertisement it is a message that communicates the routers local routing topology to all other local routers in the same ospf area. An ospf area is a logical segment or a subdomain containing networks, routers and links sharing the same area id. T nssa adds the internal route to the default route.
Lsa flooding lsa has to be processed on each routerlsa has to be processed on each router need for reliable and loopneed for reliable and loopfree floodingfree flooding on lsa arrivalon lsa arrival if router already has this version i. Dead is the time it will wait after which it will break the neighborship and inform routing table for removing the route or connected route. The ospf database of r4 is similar to that of r7 with three lsa types 1, 2 and 3. If in a drbdr multiaccess environment, the lsu, and thereby lsa, are sent to the multicast of 224. Advancing from last weeks discussion on ospf network types, todays topic is a source of considerable confusion for many people new to ospf. Router lsa type 1 contains a list of all links local to the router, and the status and cost of those links.
Notsostubby area, ospf, ospf lsa types, ospf virtual link, stubby area, totally stubby area virtual links. This lsa type can not pass throught the abr area border router and can not go to the other areas. Ospf adheres to the following link state characteristics. Ospf open shortest path first is a popular linkstate routing protocol. Prevention ospf areas should be defined as stub to prevent accidental redistribution of ebgp into ospf type 3 lsa filtering should be used at abrs and only routers loopbacks should be allowed to leak into other areas loopback should be in private address space to make lsa type 3 filtering easier. Rs coming up soon cisco live 2015 i figured this would be a good time to back over some basics, and when it comes to ospf what is more basic than ospf lsa types. Ospf allows 5 different area types, which provides flexibility, fast convergence and scalability. Link lsa lsa type 8 and intraareaprefix lsa type 9 cisco. What is the difference between dd,lsrequest,lsupdate,lsack packets and router lsa 2. As lsa type 5 is not allowed in nssa areas, a solution to that was thought as lsa 7. The linkstate advertisement lsa is a basic communication means of the ospf routing protocol for the internet protocol ip. Ospf utilizes different types of ospf routers which are determined by the role and location of a router within an ospf domain.
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. The linkstate advertisement lsa is a basic communication means of the ospf routing. This article contains list of ospf lsa types with a short description. The link ids of type 3 lsa are the destination network addresses. Pdf a practical approach to ospf link state advertisement lsa. One of the hardest things for me in my ccnp route studies was to remember the different lsa types. Every ospf router maintains a link state database lsdb.
Ospf areas and area types ospf provides two levels of hierarchy through the use of areas. Considers only the cost of the outgoing interface to the external destination. In this intermediate level tutorial, we introduce you to the different ospf area types. Before we begin, lets take a quick look at the different type of ospf lsa packets well cover. Five types of ospf routing protocol packets hello packet type 1 database description packet type 2 linkstate request packet type 3 linkstate update packet type 4 linkstate acknowledgement packet type 5. Lsa types used for open shortest path first ospf v3.