Planet XGS3-42000R User Manual page 306

switch in an OSPF area, and is sent to all other neighboring Layer 3 switch in this area; network LSA is
generated by designated Layer 3 switch in the OSPF area of multi-access network and is sent to all other
neighboring layer3 switches in this area.(To reduce data traffic among each Layer 3 switches in the
multi-access network, "designat ed layer3 switch" and "backup designated layer3 switch" should be selected in
the multi-access network, and the network link-state is broadcasted by designat ed Layer 3 switch); the
inter-area prefix LSA and inter-area router LSA are generated by OSPF area border Layer 3 s witches and
transferred among those s witches. The autonomic system exterior LSA is generated by autonomic system
exterior border Layer 3 switches and trans ferred in the whole autonomic system. Link LSA is generat ed 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 databas e. 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 S TUB area, Layer 3 switches on the area border of S TUB area announces to default routes
of S TUB area by inter-area prefix LSA; these default routes only flood in S TUB area, not outside of S TUB
area. Each STUB area has a corresponding default route, the route from S TUB area to AS exterior
destination depends only on default route of this area.
The following simply outlines the route calculation process of OSPFv3 protocol:
1. 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) packets. Thus, each layer3 switches receives
LSAs from ot her lay er3 switches, and all LSAs combined to the link-state databas e.
2. 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 s ame
autonomous system will have the same net work topology map.
3. Each layer3 switch uses the shortest path first (SPF) algorithm to calculate a tree of shortest path root ed
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 mark ed by the layer3 s witch 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 IE TF, the OSPF v3 used now is fulfilled according to the content
described in RFC2328 and RFC2740.
As a result of continuous development of IP v6 network, it has the network environment of nonsupport IP v6
sometimes, so it needs to do the IP v6 operation by tunnel. Therefore, our OSPFv3 supports configuration on
configure tunnel, and passes through nonsupport IP v6 network by unicast packet of IP v4 encapsulation.
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