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ThinkMo EDU Share – network 47.Fundamentals of Routing Protocols

蒂娜 No Comments 11/10/2022

ThinkMo EDU Share – network 47.Fundamentals of Routing Protocols


The router forwards the data packet according to the routing control table (Routing Table). It compares the IP address of the target host in the received data packet with the routing control table to obtain the next router that should be received.

Routing control is divided into two types: static and dynamic. Static routing refers to the method of setting routers and hosts in advance and fixing the routing information, and dynamic routing refers to the method of allowing routing protocols to automatically set routing control information during the running process.

Classification of Routing Protocols

Routing protocols are roughly divided into two categories, one is the Exterior Gateway Protocol ( EGP ), and the other is the Interior Gateway Protocol ( IGP ). Among them, EGP is mainly used for communication between different organizations, while IGP is used for communication within organizations.

Routing algorithm

There are two most representative ones, Distance-Vector algorithm and Link-State algorithm.

  • Distance vector algorithm

Distance Vector Algorithm (DV) refers to a method of determining the location of a target network or target host based on distance (cost) and direction.

  • Link State Algorithm

The link state algorithm is a method for the router to generate the routing control table on the basis of knowing the overall connection state of the network. In this method, each router must maintain the same information in order to perform correct routing.

In order to realize the above mechanism, the price paid by the link state algorithm is how to obtain the routing information table from the network agent. This process is very complicated, especially in a large-scale and complex network structure, management and processing of agent information requires high-speed CPU processing. capacity and lots of memory.

RIP protocol

It is a routing protocol of distance vector type and is widely used in LAN. It broadcasts routing control information to the entire network periodically (every 30 seconds). If no routing control information is received, the connection is disconnected.

However, this may be caused by packet loss, so RIP stipulates that after waiting 6 times (180 seconds) without receiving the routing message, the connection will be closed.

OSPF protocol

It is a link-state routing protocol based on the IS-IS protocol of OSI. Since the link state type is used, stable routing control can be performed even if there is a loop in the network.

In addition, OSPF supports subnet masks , thereby realizing network routing control of variable-length subnet structures, which was previously impossible in RIP.

BGP protocol

Border Gateway Protocol is a protocol that connects different organizations (or different autonomous systems), and it is a path vector protocol. Therefore, it belongs to the Exterior Gateway Protocol (EGP).

Specifically, it is mainly used for the connected part between ISPs. Only when BGP, RIP and OSPF jointly perform route control, can route control of the entire Internet be performed.


Nowadays, in addition to routing technology, label switching technology is also used in the process of forwarding IP data packets. Routing technology forwards based on the principle of the longest match in IP addresses, while label switching sets a value called “mark” for each IP packet, and then forwards according to the “mark”.

MPLS labels do not map directly to hardware devices as MAC addresses do. Therefore, MPLS does not need to have the functions of data link layer protocols such as Ethernet or ATM, but only needs to focus on the functions and protocols between it and the IP layer of the next layer.


The first is fast forwarding . Usually, when a router forwards an IP packet, it first compares the destination address with the variable-length network address in the routing control table, and then selects the longest matching path before forwarding.

This is not the case with MPLS, which uses fixed-length label information to make processing simple and forwarding through high-speed hardware.

The second advantage is to use the mark to generate a virtual path, and realize the communication of data packets such as IP on it.

Based on these characteristics, the IP network called “Best-Effort” can also provide functions such as communication quality control, bandwidth guarantee and VPN based on MPLS.

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