Planet XGS3-24042 User Manual download pdf (Page 326)

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In one word, LSA can only be transferred between neighboring Layer3 switches, and OSPFv3 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 Layer 3

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, “designated layer3 switch” and “backup designated layer3 switch” should be selected in

the multi-access network, and the network link-state is broadcasted by designated Layer 3 switch); the

inter-area prefix LSA and inter-area router LSA are generated by OSPF area border Layer 3 switches and

transferred among those switches. The autonomic system exterior LSA is generated by autonomic system

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:

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 other layer3 switches, and all LSAs combined to the link-state database.

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 same

autonomous system will have the same network topology map.

3. Each layer3 switch uses the shortest path first (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.

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Planet XGS3-24042 User Manual Page 326