Home / Cisco R&S / OSPF LSA types - Part 1

OSPF LSA types - Part 1

OSPF uses an LSDB (link state database) and fills this with LSAs (link state advertisement). Instead of using 1 LSA packet OSPF has many different types of LSAs and in this tutorial,  in the next few posts we will learn about all type of SLAs

Fig 1.1

OSPF LSA Types
LSA Type 1:            Router LSA
LSA Type 2:            Network LSA
LSA Type 3:            Network Summary LSA
LSA Type 4:            Summary ASBR LSA
LSA Type 5:            Autonomous system external LSA
LSA Type 6:            Multicast OSPF LSA
LSA Type 7:            Not-so-stubby area LSA
LSA Type 8:            External attribute LSA for BGP

Router LSA in Details:
Generated by: Every Router in an Area.
Link-State ID: Originating router ID.

This LSA is flooded by every router within an area so it does not cross the ABR.  The LSA consists of information about directly connected links. Here is the Live capture as below Figure 1.2:

Fig 1.2
You can see that there are some important fields as LS Age, Link State ID, Metric, Sequence Number, and a number of links. This LSA has been shared from a DR router. 

Let's Look an LSA type 1 format if Send by the other routers (not from DR) as below Figure 1.3:

Fig 1.3
Network LSA in Details:
Generated by: DR router only.
Link-State ID: DR Interface ID.

Generated by the DR Router on the broadcast network.  It includes the network ID, subnet mask and also the list of attached routers in the transit. This LSA also can be flooded only within the area and cannot cross the ABR. Let's look closely in Figure 1.4:

Fig 1.4


We will come up further in our next article soon.

An Article By Deepak Kumar