Planet XGS3-42000R User Manual page 305

The features of OSPFv3 protocol include the following: OSPFv3 supports networks of various scales, several
hundreds of layer3 switches can be supported in an OSPFv3 net work. Routing topology changes can be
quickly found and updating LSAs can be sent immediately, so that routes converge quickly. Link-state
information is used in shortest path algorithm for rout e calculation, eliminating loop route. OSPFv3 divides the
autonomous system intro areas, reducing database size, bandwidth occupation and calculation load.
(According to the position of layer3 switches in the autonomous system, they can be grouped as internal area
switches, area edge s witches, AS edge switches and backbone switches). OSPFv3 supports load balance
and multiple routes to the same destination of equal costs. OSPFv3 supports 4 level routing mechanisms
(process routing according to the order of route inside an area, route bet ween areas, type 1 external route
and type 2 external rout e). OSPFv3 support IP subnet and redistribution of routes from the other routing
protocols, and interface-based packet verification. OSPFv3 supports sending packets in multicast.
Each OSPFV3 layer3 switch maintains a database describing the topology of the whole aut onomous system.
Each layer3 switch gat hers the local status information, such as available int erface, reachable neighbors, and
sends link-state advertisement (sending out link-state information) to exchange link -state information with
other OSPFv3 layer3 s witches to form a link-state database describing the whole autonomous system. Each
layer3 switch builds a shortest path tree rooted by itself according to the link-state database, this tree provide
the routes to all nodes in an autonomous system. If two or more layer3 s witches exist (i.e. multi-access
network), "designat ed lay er3 s witch" and "backup designated layer3 switch" will be selected. Designated
layer3 switch is responsible for spreading link-state of the network. This concept helps reducing the traffic
among the Layer3 switches in multi-access network.
OSPFv3 protocol requires the autonomous system to be divided int o areas. That is to divide the autonomous
system into 0 area (backbone area) and non-0 areas. Routing information between areas are further
abstracted and summarized to reduce the bandwidth required in the network. OSPFv3 uses four different
kinds of routes: they are the route inside the area, route between areas, type 1 external route and type 2
external route, in the order of highest priority to lowest. The route inside an area and between areas describe
the internal net work structure of an autonomous system, while external routes describe external routes
describe how to select the routing information to destination outside the autonomous system. The first type of
exterior route corres ponds to the information introduced by OSPFv3 from the other interior routing protoc ols,
the costs of those routes are comparable with the costs of OSPFv3 rout es; the second type of exterior route
corresponds to the information introduced by OSPFv3 from the other exterior routing protocols, but the costs
of those routes are far greater than that of OSPFv3 routes, so OSPFv3 route cost is ignored when calculating
route costs.
OSPFv3 areas are centered with the Backbone area, identified as the Area 0, all the other areas must be
connected to Area 0 logically, and Area 0 must be continuous. For this reason, the concept of virt ual link is
introduced to t he backbone area, so that physically separated areas still have logical connectivity to the
backbone area. The configurations of all the layer3 switches in the same area must be the same.
In one word, LSA can only be transferred between neighboring Lay er3 switches, and OSPF v3 protocol
includes seven kinds of LSA: link LSA, internal-area prefix LSA, router LSA, network LSA, inter-area prefix
LSA, inter-area router LSA and autonomic system exterior LSA. Router LSA is generated by each Lay er 3
38-2