Type 1 LSA in OSPF

EdTheLadEdTheLad Member Posts: 2,112 ■■■■□□□□□□
Type 1 LSAs describe the state of all interfaces on a router i.e. all the directly connected ip networks.These LSA's are identified in the Link state database by their router ID.
Now i'm not sure exactly what size the IP packet is for the LSA, lets say less than 1500bytes the standard ethernet frame.Now what happens if i have a hugh number of ip networks directly connected on subinterfaces like a frame-relay switch.If these networks are too many to fit in the LSA will two LSAs be generated corresponding to the same Router ID?
If so how will this be displayed in the Link State Database?
Is the LSA split into multiple IP packets and only referenced once in the Database?
Networking, sometimes i love it, mostly i hate it.Its all about the $$$$

Comments

  • kypumperkypumper Member Posts: 35 ■■□□□□□□□□
    OSPF type 1 messages are based on Hello Protocol.
    type 2 is a EXSTART router will send info about its Link State databse.
    type 3 is a Link State Request.
    type 4 is a Link State advertisement when a router receives this it will rerun the SPF algorithm to recalculate its routing table.
    type 5 is a Link State Acknowledge.

    I am not sure if type 2 through 5 are also based on Hello Protocol or if they are just multicast to all routers using 224.0.0.5
    I love the Search Function!
  • EdTheLadEdTheLad Member Posts: 2,112 ■■■■□□□□□□
    My question was specific, i didnt ask what are type 1 LSA's.Does a type 1 LSA consist of multiple packets or only one?If there is to much info to fit in one packet what happens?Would 2 LSA be generated?how are these represented in the database?

    Oh and just to point out your info above is incorrect!
    Networking, sometimes i love it, mostly i hate it.Its all about the $$$$
  • kplabkplab Member Posts: 101
    What kypumper mentioned is the OSPF packet types, rather than the LSA types. There are 5 types of OSPF packets. Type 4 OSPF packet is link-state update (LSU) packet, which is used to carry various types of LSAs.

    Come back to ed_the_lad's question. Each LSU packet can carry one or more LSAs. A router-LSA (i.e. Type 1 LSA) must describe all of the originating router's links to the area in which the LSA is flooded. If the router has many interfaces, the size of the router-LSA will be quite large. Since OSPF runs over IP, the LSU packet containing the router-LSA is encapsulated in an IP datagram. If the IP datagram size is larger than the link MTU, the datagram will be fragmented just like any other IP datagrams.
    KPLAB
    www.kp-lab.com - Free CCNA, CCNP, and Network+ Study Guides
Sign In or Register to comment.