Accton Technology ES4626 - Manual (Page 486)

486
exterior border Layer 3 switches and transferred in the whole autonomic system. Link
LSA is generated by Layer 3 switch on the link and sent to other Layer 3 switches on the
link. Internal-area prefix LSA is generated by designated layer3 switch of each link in this
area, and flooded to the whole area.
For autonomous system focused on exterior link-state announcement, OSPFv3 allow
some areas to be configured as STUB areas in order to reduce the size of topological
database. Router LSA, network LSA, inter-area prefix LSA, link LSA, internal-area prefix
LSA are permitted to advertise to STUB area. Default route must be used in STUB area,
Layer 3 switches on the area border of STUB area announces to default routes of STUB
area by inter-area prefix LSA; these default routes only flood in STUB area, not outside of
STUB area. Each STUB area has a corresponding default route, the route from STUB
area to AS exterior destination depends only on default route of this area.
The following simply outlines the route calculation process of OSPFv3 protocol:
a) Each OSPF-enabled layer3 switch maintains a database (LS database) describing
the link-state of the topology structure of the whole autonomous system. Each layer3
switch generates a link-state advertisement according to its surrounding network
topology structure (router LSA), and sends the LSA to other layer3 switches through
link-state update (LSU) packages. Thus, each layer3 switches receives LSAs from
other layer3 switches, and all LSAs combined to the link-state database.
b) Since a LSA is the description of the network topology structure around a layer3
switch, the LS database is the description of the network topology structure of the
whole network. The layer3 switches can easily create a weighted vector map
according to the LS database. Obviously, all layer3 switches in the same autonomous
system will have the same network topology map.
c) Each layer3 switch uses the shortest path finding (SPF) algorithm to calculate a tree
of shortest path rooted by itself. The tree provides the route to all the nodes in the
autonomous system, leaf nodes consist of the exterior route information. The exterior
route can be marked by the layer3 switch broadcast it, so that additional information
about the autonomous system can be recorded. As a result, the route table of each
layer3 switch is different.
OSPFv3 protocol is developed by the IETF, the OSPF v3 used now is fulfilled
according to the content described in RFC2328 and RFC2740.
As a result of continuous development of IPv6 network, it has the network
environment of nonsupport IPv6 sometimes, so it needs to do the IPv6 operation by
tunnel. Therefore, our OSPFv3 supports configuration on configure tunnel, and passes
through nonsupport IPv6 network by unicast packet of IPv4 encapsulation.
13.7.2 OSPFv3 Configuration Task List