SGS-6341-Series User Manual

network. This proces
s is referred to as “flooding”. In this way, firsthand information is sent
throughout the network to provide accurate map for creating and updating routes in the
network. Link-state routing protocols use cost instead of hops to decide the route. Cost is
assigned automatically or manually. According to the algorithm in link-state protocol, cost can
be used to calculate the hop number for packets to pass, link bandwidth, and current load of
the link. The administrator can even add weight for better assessment of the link-state.
1) When a link-state Layer 3 switch enters a link-state interconnected network, it sends a
HELLO packet to get to know its neighbors and establish neighborhood.
2) The neighbors respond with information about the links they are connecting and the
related costs.
3) The originate Layer 3 switch uses this information to build its own routing table
4) Then, as part of the regular update, Layer 3 switch send link-state advertisement (LSA)
packets to its neighboring Layer 3 switches. The LSA include links and related costs of
that Layer 3 switch.
5) Each neighboring Layer 3 switch copies the LSA packet and passes it to the next
neighbor (i.e. flooding).
6) Since routing database is not recalculated before Layer 3 switch forwards LSA flooding,
the converging time is greatly reduced.
One major advantage of link-state routing protocols is the fact that infinite counting is
impossible, this is because of the way link-state routing protocols build up their routing table.
The second advantage is that converging in a link-state interconnected network is very fast,
once the routing topology changes, updates will be flooded throughout the network very soon.
Those advantages release some Layer 3 switch resources, as the process ability and
bandwidth used by bad route information are minor.
The features of OSPF protocol include the following: OSPF supports networks of various
scales, several hundreds of Layer 3 switches can be supported in an OSPF network. 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 route
calculation, eliminating loop route. OSPF divides the autonomous system into areas, reducing
database size, bandwidth occupation and calculation load. (According to the position of Layer
3 switches in the autonomous system, they can be grouped as internal area switches, area
border switches, AS border switches and backbone switches). OSPF supports load balance
and multiple routes to the same destination of equal costs. OSPF supports 4 level routing
mechanisms (process routing according to the order of intra-area path, inter-area path, type 1
external path and type 2 external path). OSPF supports IP subnet and redistribution of routes
from the other routing protocols, and interface-based packet verification. OSPF supports
sending packets in multicast.
Each OSPF Layer 3 switch maintains a database describing the topology of the whole
autonomous system. Each Layer 3 switch gathers the local status information, such as
available interface, reachable neighbors, and sends link-state advertisement (sending out
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User’s Manual of SGS-6341 series