SGS-6341-Series User Manual

summary LSA) and type5 LSA (AS external LSA
) are not allowed to flood into/through STUB
areas. STUB areas must use the default routes, the Layer 3 switches on STUB area edge
advertise the default routes to STUB areas by type 3 summary LSA, those default routes only
floods inside STUB area and will not get out of STUB area. Each STUB area has a
corresponding default route, the route from a STUB area to AS exterior destination must rely
on the default route of that area.
The following simply outlines the route calculation process of OSPF protocol:
1） Each OSPF-enabled Layer 3 switch maintains a database (LS database) describing
the link-state of the topology structure of the whole autonomous system. Each Layer
3 switch generates a link-state advertisement according to its surrounding network
topology structure (router LSA), and sends the LSA to other Layer 3 switches through
link-state update (LSU) packets. Thus each Layer 3 switches receives LSAs from
other Layer 3 switches, and all LSAs are combined to the link-state database.
2） Since a LSA is the description of the network topology structure around a Layer 3
switch, the LS database is the description of the network topology structure of the
whole network. The Layer 3 switches can easily create a weighted vector map
according to the LS database. Obviously, all Layer 3 switches in the same
autonomous system will have the same network topology map.
3） Each Layer 3 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 Layer 3 switch broadcast it, so that additional information
about the autonomous system can be recorded. As a result, the route table of each
Layer 3 switch is different.
OSPF protocol is developed by the IETF, the OSPF v2 widely used now is fulfilled according to
the content described in RFC2328.
26.5.2 OSPF Configuration Task List
The OSPF configuration for SGS-6341 Series switches may be different from the configuration
procedure to switches of the other manufacturers. It is a two-step process:
Enable OSPF in the Global Mode;2, Configure OSPF area for the interfaces. The configuration
task list is as follows:
1. Enable OSPF protocol (required)
(1) Enable/disable OSPF protocol (required)
(2) Configure the ID number of the Layer 3 switch running OSPF (optional)
(3) Configure the network scope for running OSPF (optional)
(4) Configure the area for the interface (required)
2. Configure OSPF protocol parameters (optional)
(1) Configure OSPF packet sending mechanism parameters
1) Configure OSPF packet verification
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User’s Manual of SGS-6341 series