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Router LSA

This type of LSA is distributed by all the routers within the same area.

The LSA contains the following routing information:

• a description of all router communication channels related to the routes to the networks included in this area;
• the router communication channels costs of the routes;
• a list of area routers with established neighborhood relationship.

• routers inside the routing area, specifying the established neighboring relations.

This type of LSA is distributed by all the routers in the network (Figure 5b).

This LSA type has the following features:

• R3 will include only the 10.10.234.0/29 network information in the LSA type 1 broadcasted in area 0, and the 192.168.36.0/24 network information in LSA broadcasted in area 36. This behavior is explained by the fact that LSA type 1 is designed to exchange information within an area;
• Router R5 does not generate an LSA type 1 with information about the external network 172.16.0.0/16;
• Type The type 1 LSA generated by R4 will be received by R2 and forwarded to R1 with the an increased metric value. Thus, LSA type 1 are is propagated over the entire area with metric increments, the rest of the parameters remain remaining unchanged.

Network LSA

LSA of this type are This type of LSA is distributed by the DR within the same area.

The LSA contains the following routing information:

• the broadcast's segment network address;
• the broadcast's segment network mask;
• a list of routers with the established neighborhood relationshipneighboring relations.

LSA of this type are This type of LSA is generated only by routers with having a DR role - R1, R2, R3 and R4 (Figure 5c).

Similar to LSA type 1, LSA type 2 is distributed across the entire area with metric value increments.

Summary Network LSA

LSA of this type are This type of LSA is distributed by ABR and contain routing information about the neighboring area. The the ABR and contains a summary of the routes in one area, that it is intended to be sent through the interfaces included in different area. LSA types 1 and 2 allow the router to build an a topology of the area topology and calculate the data transmission paths. Type 3 LSA LSAs are not sources of topology data, they only contain routing information about the neighboring areas. Thus, at the areas area borders, OSPF behaves as a distance vector protocol.

The ABR generates one LSA type 3 for each network. The messages number of LSA type 3 messaged can be reduced by routes using route summarization.

LSA of this type are This type of LSA is generated by ABR routers - R3 and R4 (Figure 5d).

The R3 router generates the following LSA type 3 messages:

• route to the 192.168.36.0/24 network for area 0. R3 router connected to this network via eth1 interface;of area 36 that will be sent to area 0 through the eth0 interface.
• route to the 10.10.234.0/29 network for of area 0 that will be sent to area 36 . R3 router connected to this network via eth0 interface;through the eth1 interface.
• route tothe 10.10.21.0/30 network for of area 0 that will be sent to area 36 . Network through the eth1 interface. This network information is taken from LSA types 1 and 2 received from R1;
• route to the 192.168.45.0/24 network for of area 45 that will be sent to area 36 through the eth1 interface. The route to this network is taken from the LSA type 3 received from router R4. During When advertising this network, router R3 setting sets itself as the route source in the LSA. Source substitution is necessary, since the 36 area router is routers in area 36 are unaware of the R4's location.

Router R4 generates LSA type 3 in the same way as R3.

ASBR Summary LSA

LSA of this type an ABR generates in addition to LSA type 5.

LSA of this type contain information about the ASBR location for the neighboring to ASBR area.

External LSA

LSA of this type are generated by ASBR for external routes, including default routes. Such messages are distributed throughout the AS unchanged.

Similar to ABR, ASBR can summarize external routes, i.e. replace several routes with one. This reduce the routing table and the service information amount during the further routes distribution.

LSA type 5 is generated by R5 as the only ASBR in the network scheme (Figure 5e).

The type 5 LSA generated by R5 contains information about the 172.16.0.0/16 network and is distributed through the entire autonomous system unchanged. Thus, each router in the scheme has information that the 172.16.0.0/16 network is an external and is available via the R5 router.

The hidden problem is that R1, R2, R3, and R6 do not know the R5 location. LSA type 1 where the the R5 ID specified is only propagated within area 45.

To solve this problem, border routers R4 and R3 generate LSA type 4 in addition to the transmitted LSA type 5. In LSA type 4, routers advertise that all traffic directed to R5 can be sent to ABR.

Group Membership LSA

LSAs of this type are used in Multicast networks and contain a list of groups whose consumers are in the network segment. LSA of this type will not be described in this article.

Type 7 LSA