Lsas; Point-To-Point Versus Multi-Access Networks - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring OSPF
13-30
You will recall that a routing protocol must dictate options such as:
how routers compute a route's metric and select the best route for their
routing table
what information routers include in routing updates
which routers and router interfaces send and receive updates
when routers send and receive updates
You can read this overview to learn in more detail how OSPF handles such
options. The most important concepts to understand are:
how routers use the information in LSAs to synchronize their topological
databases
how routers compute best routes from their topological database
how areas divide networks into separate routing domains
how internal routers handle intra-area routing for stub areas
how ABRs handle inter-area routing through the network backbone

LSAs

OSPF is a link-state protocol; routers send each other LSAs to distribute
information about their connections to networks and to other routers. LSAs
help routers synchronize their databases. All routers in an AS (or area) must
use the same database in order to generate accurate routes.
OSPF defines several types of LSAs. Some of these LSAs are flooded to all
routers or DRs in an area, and some are sent to routers throughout the entire
AS. Interfaces in stub areas do not listen for certain LSAs. (You can read more
about different types of LSAs in "LSA Types" on page 13-33.)
OSPF defines specific rules for synchronizing databases with a minimum of
traffic between routers. Any two routers that have interfaces on the same
network are neighbors that could potentially send each other LSAs. However,
not all neighbors establish full adjacency—that is, exchange LSAs. OSPF
institutes protocols by which all routers can synchronize their databases
without all of them exchanging LSAs.

Point-to-Point Versus Multi-Access Networks

In a point-to-point network, a router establishes full adjacency only with the
routers to which it is directly connected. All WAN connections on the
ProCurve Secure Router are point-to-point. Even Frame Relay networks rely
on point-to-point permanent virtual circuits (PVCs) connected through Frame
Relay subinterfaces.