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OSPF in Industrial 4G Router
OSPF Origin
In order to meet the growing need for building IP-based networks, the IETF has developed a working group dedicated to the development of open link-state routing protocols for use in large, heterogeneous IP networks. The new routing protocol has been based on a number of successful private, manufacturer-related, shortest path first (SPF) routing protocols that are widely used in the market. All SPI routing protocols, including OSPF, are based on a mathematical algorithm, the Dijkstra algorithm. This algorithm enables routing based on link state rather than distance vector. OSPF was developed by the IETF in the late 1980s, and OSPF is an open version of the SPF class routing protocol. The original OSPF specification is now in RFC1131.
A link is another term for a router interface, so OSPF is also known as an interface state routing protocol. OSPF establishes a link state database by advertising the state of the network interface between routers to generate a shortest path tree, and each OSPF router uses these shortest paths to construct a routing table.
The OSPF routing protocol is a typical link-state routing protocol and is generally used in the same routing domain. Here, a routing domain refers to an autonomous system (Autonomous System), which is a group of networks that exchange routing information with each other through a unified routing policy or routing protocol. In this AS, all OSPF routers maintain a database describing the AS structure. The database stores the status information of the corresponding link in the routing domain. The OSPF router calculates the OSPF routing table through this database. of.
As a link state routing protocol, OSPF transmits Link State Advertisement (LSA) to all routers in a certain area, which is different from the distance vector routing protocol. A router running a distance vector routing protocol passes some or all of the routing table to its neighboring routers.
OSPF Area
Because OSPF routers exchange all link states (LSAs) with each other, they do not retain them. When the network scale reaches a certain level, the LSA will form a huge database, which will inevitably bring tremendous pressure to OSPF computing; It can reduce the complexity of OSPF calculation and cache calculation pressure. OSPF uses sub-area calculation to divide all OSPF routers in the network into different areas. Each area is responsible for accurate LSA transfer and route calculation in each area, and then an area is used. The LSA is simplified and aggregated and then forwarded to another area, so that within the area, there is a network-accurate LSA, and in different areas, a simplified LSA is delivered. The division of the area is designed to be designed as a loop-free network, so the topology of Hub-Spoke is adopted, that is, the topology of the core and the branch is adopted.
NetworkTypes of OSPF
1. OSPF is a true LOOP- FREE (no route self-loop) routing protocol. From the advantages of its algorithm itself. (link state and shortest path tree algorithm)
2. Broadcast network (broadcast), the network type proposed by cisco, automatically discovers neighbors, elects DR/BDR, hello time 10s.
2.1 Broadcast network, such as Ethernet, Token Ring and FDDI, will elect a DR and BDR on the network. The destination address of the OSPF packet sent by DR/BDR is 224.0.0.5, and the destination MAC of the frame carrying these OSPF packets. The address is 0100.5E00.0005; the destination address of the OSPF packet sent except for DR/BDR is 224.0.0.6. This address is called All D-Routers.
3. Non-broadcast (NBMA) network (non-broadcast), the type of network proposed by the RFC, manually configuring neighbors, electing DR/BDR, and hello time 30s.
3.1. NBMA networks, such as X.25, Frame Relay, and ATM, do not have the ability to broadcast, so neighbors must be manually specified. On such networks, DR and BDR should be elected, and OSPF packets should be unicast.
4. Point-to-multipoint (point-to-multipoint), proposed by the RFC, automatically discovers neighbors, does not elect DR/BDR, hello time 30s.
4.1 Point-to-multipoint network is a special configuration of NBMA network, which can be regarded as a collection of point-to-point links. DR and BDR are not elected on such networks.
5. Point-to-multipoint non-broadcast, the type of network proposed by cisco, manually configure neighbors, do not elect DR/BDR, hello time 30s.
6. Virtual link: OSPF packet is sent as unicast
Main Advantages of OSPF Protocol
1. OSPF is a true LOOP- FREE (no route self-loop) routing protocol. From the advantages of its algorithm itself. (link state and shortest path tree algorithm)
2. OSPF convergence speed is fast: the routing changes can be transmitted to the entire autonomous system in the shortest time.
3. The concept of area division is proposed. After the autonomous system is divided into different areas, the number of routing information to be transmitted is greatly reduced by summarizing the routing information between the areas. It also makes routing information not expand rapidly as the network scales up.
4. Control the overhead of the protocol itself to a minimum.
1) It is used to discover and maintain neighbor relationships. It is a hello packet that is sent periodically without routing information. It is very short. The message containing the routing information is the mechanism that triggers the update. (Sent when there is a route change). However, in order to enhance the robustness of the protocol, it is resent every 1800 seconds.
2) In the broadcast network, the multicast address is used instead of the broadcast to send packets, which reduces interference to other network devices that do not runOSPF.
3) In all types of networks that can be accessed multiple times (broadcast, NBMA), by electing DR, the number of route exchanges (synchronization) between routers on the same network segment is reduced from O(N*N) times to O (N). ) times.
4) Propose the concept of the NSSA area so that the introduced ASE route is no longer propagated in the NSSA area.
5) Support route aggregation on ABR (area border router) to further reduce routing information between areas.
6) In the point-to-point interface type, OSPF over-on-demand circuits are configured to prevent ospf from sending hello packets and updating routing information periodically. Update information is sent only when the network topology really changes.
5. Provide more reliable routing by strictly dividing the level of routing (four poles in total).
6. good security,OSPF supports interface-based plaintext and md5 authentication.
7. OSPF adapts to networks of various sizes, up to thousands.
OSPF is the first widely deployed routing protocol that can converge a network in a few seconds and guarantee loop-free paths. It has many features that allow the imposition of policies about the propagation of routes that it may be appropriate to keep local, for load sharing, and for selective route importing more than IS-IS.
Actually besides OSPF, there are BGP, Rip, IS-IS, IGRP, EIGRP and other dynamic route protocols. E-Lins industrial 4g router can cover all these protocols with customized development and support.
