Understand Open Shortest Path First (ospf) Design Guide

LS
Type
Link State ID (In the high level view of the database when a router is referenced, this is called
Link ID)
1
The origin Router ID (RID).
2
The IP interface address of the network Designated Router.
3
The destination network number.
4
The router ID of the described AS boundary router.
5
The external network number.
The different links available:
Stub network links: This term has nothing to do with stub areas. A stub segment is a segment
that has one router only attached to it.

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An Ethernet or Token Ring segment that has one attached router is considered a link to a stub
network. A loopback interface is also considered a link to stub network with a 255.255.255.255
mask (Host route).
Point-to-point links: These could be physical or logical (subinterfaces) point-to-point serial link
connections. These links could be numbered (an IP address is configured on the link) or
unnumbered.
Transit links: These are interfaces connected to networks that have more than one router
attached, hence the name transit.
Virtual links: These are logical links that connect areas that do not have physical connections to
the backbone. Virtual links are treated as numbered point-to-point links.
The link-ID is an identification of the link itself. This is different for each link type.
A transit link is identified by the IP address of the DR on that link.
A numbered point-to-point link is identified by the RID of the neighbor router on the point-to-
point link.
Virtual links are identical to point-to-point links.
Stub network links are identified by the IP address of the interface to the stub network. This table
summarizes this information: