Our previous short article explained the objective of attach State update (LSU) packets and also examined the Link State Advertisement (LSA) information had within LSU packets. We likewise saw the most usual LSA packets discovered in OSPF networks. In this short article we’ll it is in diving deeper come analyse all eleven OSPF LSA Types making use of network network diagrams and examples to assist understand as soon as each LSA type is used and also how they store the OSPF network updated.

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LSA types - fast Overview

Before us begin, let’s take a quick look at the different type of OSPF LSA packets we’ll cover:

LSA kind 1: OSPF Router LSALSA type 2: OSPF Network LSALSA type 3: OSPF an overview LSALSA type 4: OSPF ASBR review LSALSA kind 5: OSPF ASBR outside LSALSA type 6: OSPF group Membership LSALSA type 7: OSPF no So Stubby Area (NSSA) external LSALSA kind 8: OSPF External features LSA (OSPFv2) / attach Local LSA (OSPFv3)LSA form 9: OSPF link Scope Opaque (OSPFv2) / Intra Area Prefix LSA (OSPFv3)LSA form 10: OSPF Area border Opaque LSALSA form 11:OSPF together (Autonomous System) scope Opaque LSA

The LSA payload different in size according to the LSA type and the information it includes. The diagram below clearly shows just how LSAs are consisted of within LSUs:


Figure 1. LSA species contained within an OSPF LSU packet

As mentioned, OSPF currently supports 11 varieties of LSAs. Each LSA is supplied within specific boundaries of one OSPF network.

OSPF concepts, consisting of router duties such as Designated Router (DR), Area Border Router (ABR), Autonomous mechanism Border Router (ASBR), OSPF Areas and also more, are analyzed in great depth in our article OSPF straightforward Concepts – OSPF areas – Router Roles. This write-up assumes the reader has a good understanding of an easy OSPF theory and also is comfortable v OSPF concepts.

LSA form 1 – OSPF Router LSA

LSA kind 1 (Router LSA) packets space sent between routers in ~ the very same area that origin and also do not leave the area. An OSPF router supplies LSA type 1 packets to explain its own interfaces but likewise carries information about its next-door neighbors to adjacent routers in the exact same area.


Figure 2. LSA kind 1 Packets exchanged between OSPF routers in ~ the exact same area

LSA form 2 – OSPF Network LSA

LSA form 2 (Network LSA) packets are created by the Designated Router (DR) to explain all routers linked to its segment directly. LSA kind 2 packets space flooded in between neighbors in the exact same area that origin and also remain within that area.


Figure 3. LSA form 2 Packets exchanged in between OSPF DR and neighbor routers

LSA kind 3 – OSPF an overview LSA

LSA type 3 (Summary LSA) packets are created by Area Border Routers (ABR) to summary its directly associated area, and advertise inter-area router info to other locations the ABR is linked to, through the usage of a review prefix (e.g LSA form 3 packets space flooded come multiple locations throughout the network and help with OSPF’s scalability v the use of an introduction prefixes.


Figure 4. LSA kind 3 - one OSPF ABR router advertises the summarized path to Area 0

Looking at the diagram above, ABR router R2 creates a Type 3 an overview LSA and floods it right into Area 0. In a comparable way, ABR router R3 create a Type 3 summary LSA and floods it into Area 2. Type 3 an overview LSAs appear as O IA entries in the router routing table.

LSA kind 4 – OSPF ASBR review LSA

LSA type 4 (ASBR review LSA) packets space the LSAs that advertise the presence of one Autonomous device Border Router (ASBR) to other areas. In the example listed below when R2 (ABR) receives the LSA kind 1 packet from R1 that will create a LSA kind 4 (Summary ASBR LSA) packet, i m sorry advertises the ASBR route received from Area 1, and inject it into Area 0.


Figure 5. LSA form 4 packets injected right into Area 0 & 2 by the R2 ABR and R3 ABR

While LSA kind 4 packets are supplied by ABRs to advertise the ASBR course through your areas, it will not be provided by the ASBR itself in ~ its regional area (Area 1); ASBR provides LSA kind 1 to inform its next-door neighbors (R2 in this case) in ~ its networks.

LSA kind 5 – OSPF ASBR external LSA

LSA form 5 (ASBR external LSA) packets are produced by the ASBR come advertise external redistributed routes right into the OSPF’s AS. A usual example of an LSA kind 5 would certainly be an external prefix e.g or default route (internet) as displayed below:

Figure 6. LSA kind 5 packets advertising the default course to all OSPF routers

This external route/prefix is redistributed in come the OSPF network by the ASBR (R1) and also seenas O E1 or E2entries in various other OSPF routers routing tables.

LSA form 6 – OSPF group Membership LSA

LSA kind 6 (Group membership LSA) packets to be designed for Multicast OSPF (MOSPF), a protocol the supports multicast routing through OSPF. MOSPF is not supported by Cisco and is not extensively used and is supposed to it is in retired soon.

LSA type 7 – OSPF not So Stubby Area (NSSA) outside LSA

LSA kind 7 (NSSA external LSA) packets are supplied for some distinct area varieties that execute not permit external dispersed routes to walk through and thus block LSA kind 5 packets indigenous flooding v them, LSA kind 7 packets act as a mask because that LSA type 5 packets to permit them to relocate through these special areas and also reach the ABR that is maybe to interpret LSA form 7 packets back to LSA form 5 packets.


Figure 7. LSA kind 7 packets passing through an NSSA and also being transformed right into LSA form 5 through the ABR

In the over example, ABR R2 translates LSA Type 7 into a LSA type 5 and also floods it into the OSPF network.

LSA kind 8 - OSPF External features LSA (OSPFv2) / connect Local LSA (OSPFv3)

LSA kind 8 packets (External qualities LSA -OSPFv2-/ attach Local LSA -OSPFv3-) in OSPFv2 (IPv4) are dubbed External Attribute LSAs, and also are supplied to transit BGP characteristics through one OSPF network while BGP destinations room conveyed via LSA type 5 packets, however, this attribute isn’t sustained by many routers. Through OSPFv3 IPv6), LSA kind 8 is redefined to bring IPv6 info through OSPF network.

LSA form 9, 10 & 11

Generally Opaque LSAs (LSA kind 9, 10 & 11) are provided to extend the capabilities of OSPF enabling the protocol to bring information OSPF no necessarily care about. Helpful application of Opaque LSAs is in MPLS traffic design where they are offered to communicate interface parameters such as maximum bandwidth, unreserved bandwidth, etc. Complying with is a short evaluation of each of the 3 Opaque LSAs.

LSA kind 9 – OSPF attach Scope Opaque (OSPFv2) / Intra Area Prefix LSA (OSPFv3)

LSA form 9 in OSPFv2 (IPv4) is identified as a Link limit Opaque LSA for carrying OSPF information. Because that OSPFv3 the redefined to manage a interaction prefix because that a distinct area kind called Stub Area.

LSA form 10 – OSPF Area border Opaque LSA

LSA kind 10 packets are offered to flood OSPF details through various other area routers even if this routers execute not procedure this info in order to prolong OSPF functionality, this LSA is supplied for traffic design to advertisement MPLS and also other protocols.

LSA kind 11 – OSPF together Scope Opaque LSA

LSA kind 11 packets offer the same purpose as LSA type 10 packets yet are no flooded into special area types (Stub areas).

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In this write-up we examined every 11 OSPF LSA packet types and also explained your purposes. We likewise examined the framework of one LSA packet and also used network diagrams to assist illustrate just how LSA packets flow between routers & OSPF Areas. For much more high-quality OSPF articles visit our OSPF Section.