interfaces in more than one area:
to multiple OSPF areas.
tiple link state databases. This should be a design consideration when sizing
a router that will function as an area border router.
network with a different Process ID, or a network running any other such
external routing process, this external network may be referred to as an
autonomous system. The scenario of an OSPF router sitting at the boundary
of an external routing process leads us to a fourth category of OSPF router:
ary router is any OSPF router that is connected to an external routing process.
is connected is not an automatic process. Such routes are exchanged through
a process called route redistribution, which is the focus of Chapter 10,
"Route Optimization."
ments (LSAs). However, just as we had multiple OSPF router categories to
consider, we also have multiple types of LSAs to consider. Specifically, there
are five types of LSAs that we need to be concerned with. While the impor-
tance of LSA classification may not be immediately apparent, we will see its
application when we examine the various types of OSPF areas. Let's examine
the function of the various LSA types:
Type 1 LSA is an advertisement sent by a router to other routers in its
area. The advertisement contains the status of a router's link to the area
it is connected to. If a router is connected to multiple areas, then it will
send a Type 1 LSA for each of the areas it is connected to.