Qtech QSW-3900-24-SFP-DC [94/245] Ospf configuration

Qtech QSW-3900-48-SFP-DC [94/245] Ospf configuration
QTECH Software Configuration Manual
8-93
Chapter 8 OSPF Configuration
8.1 Brief introduction of OSPF
OSPF is short for Open Shortest Path First which is an internal route protocol based on link status and the
shortest path precedence. In IP network, it searches and transmits route dynamically through collecting and delivering
link status of autonomy system; OSPF protocol supports packet authentication based on interface to guarantee the
safety of route calculating; OSPF protocol sends and receives packets in the form of IP multicast.
Each router supported OSPF protocol maintains a database which describes the topology of the whole
autonomy. This database collects the link states advertise (LSA). Each router broadcasts information describing local
states to the whole autonomy. In each multiple accessing network, if there are two or more routers, designated router
(DR) and backup designated router (BDR) are selected. Designated router broadcasts network link states advertise
out. Introducing this concept can redeuce the number of neighborship between each router in multiple accessing
network. OSPF protocol permits autonomy system dividing into areas to be managed. Routing information
transmitted between areas will be furtherly abstracted to reduce bandwidth occupation.
OSPF uses 4 types of different routing, according to the precedence are :
· Inter Area Routing
· Area Border Routing
· The first type external routing
· The second type external routing
Inter Area Routing and Area Border Routing describe internal network structure of autonomy system;
external routing describes how to select route to the destination out of autonomy system. Generally, the first type
routing corresponds to information introduced by other internal routing protocol, the cost of which can be comparable
with that of the OSPF itself; the second type of routing corresponds the information introduced by external routing
protocol, the cost of which is far beyond that of OSPF itself. So when calculating, only external cost is considered.
According to libk state database, each router establishes a shortest path tree with the root of itself which can
give out the routing to each node in autonomy system. External routing information appears in leaf node and it can
broadcast its router to mark to keep record the extra information about autonomy system.
Areas of OSPF are connected by BackBone which with the mark of 0.0.0.0. All areas must be continuous
logically. BackBone specially introduces virtual connection to guarantee the logical connection when the area is
physically divided.
All the routers in the same area must be consensus the parameter configuration of this area. Therefore, when
configuring routers in the same area, most configuration data must be considered based on area and error
configuration may cause the non-communication of neighbour routers or routing information congestion and
self-ring.
OSPF has the following features :
· Wide scope : Supports networks of various sizes and up to several hundred routers in an OSPF routing
domain.
· Fast convergence : Transmits updates instantly after network topology changes for routing information
synchronization in the AS.
· Loop-free : Computes routes with the shortest path first (SPF) algorithm according to the collected link
states, so no route loops are generated.
· Area partition : Allows an AS to be split into different areas for ease of management and the routing
information transmitted between areas is summarized to reduce network bandwidth consumption.
· Equal-cost multi-route : Supports multiple equal-cost routes to a destination.
· Routing hierarchy : Supports a four-level routing hierarchy that prioritizes the routes into intra-area,
inter-area, external Type-1, and external Type-2 routes.
· Authentication : Supports interface-based packet authentication to guarantee the security of packet
exchange.
· Multicast : Supports packet multicasting on some types of links.

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