Route table and router Selection Algorithm

Standard route table

1. The basic idea of road selection at the next stop

The route table only specifies the next step from the router to the destination path, without knowing the complete path to the destination.

2. The standard IP route table contains many (N, R) pairs.

N: IP address of the destination network

R: IP address of the next vro on the N path.

Basic next-Stop routing selection algorithm:

Routedatasync (datasync, RoutingTable)

{

Extract the destination IP address D from datax and calculate the netid network number N;

If N matches the network address directly connected to the vro

Direct delivery of Then on the Network (encapsulation, physical address binding, sending, etc)

ElseIf RoutingTable contains routes to N

Then sends the datax to the next stop specified in RoutingTable.

Else route selection Error

}

Static Routing and Dynamic Routing

Static Routing is created and managed manually, and does not change automatically. It must be updated manually to reflect changes in the Internet Topology or connection mode.

Static Routing features:

Advantages: it is safe, reliable, simple, and intuitive, avoiding the overhead of dynamic routing selection.

Disadvantage: Not Suitable for complex Internet structures: the establishment and maintenance work is heavy, and routing loops are prone to appear.

Static Routing will not be changed automatically when a fault occurs on the Internet.

Applicable environment: relatively complex Internet Structure

Dynamic Routing can automatically modify and refresh the route table through self-learning. Dynamic Routing requires constant exchange of route information between routers.

Dynamic Routing features:

Advantage: more autonomy and flexibility

Disadvantage: Switching route information requires network bandwidth; Dynamic Modification and refresh of Route tables requires the memory and CPU processing time of the router, consuming router resources.

Applicable environment: automatically resolves error paths on the Internet with complex topology structures and a large network scale, and automatically selects paths with better performance

Path measurement value metric

Metric represents the value of a path. The smaller the metric, the better the path.

Metric computing can be based on one feature of a path or multiple features of a path.

Hop count: the number of routers that must pass through when the IP datagram arrives at the destination.

Bandwidth: The data capability of the link.

Latency: the time required to send data from the source to the destination.

Load: the number of activities in the network (such as in a router or in a link ).

Reliability: Error Rate During Data Transmission

Overhead: a variable value, which can be specified by the network administrator based on factors such as bandwidth, construction fee, maintenance fee, and usage fee.

Routing Protocol:

1. Basic conditions for using dynamic routing

The router runs the same routing selection protocol and executes the same routing selection algorithm.

2. Widely used routing protocols

Routing Information Protocol (RIP): Vector-Distance Algorithm

Open Shortest Path Priority Protocol (OSPF): uses the link-state Algorithm

3. Route convergence

Meaning: All routers on the Internet run the same routing information that is accurate enough to reflect the current Internet topology.

Fast convergence is the most desired feature of the routing selection protocol.

Routing Algorithm:

1. Vector-distance routing selection algorithm

Basic Idea: A vro periodically broadcasts its route information to its adjacent vrouters to notify neighboring routers of the network they can reach and the distance to the network. The adjacent router can modify and refresh its route table based on the received route information.

Advantages: the algorithm is simple and easy to implement.

Disadvantage: slow convergence problem: the route change of the router needs to be transmitted from the adjacent router like a wave, and the process is slow.

Large amount of information to be exchanged: similar to the size of your route table

Applicable environment: small-and medium-sized Internet with few route changes

2. Link-status routing selection algorithm

Basic Idea: Each router on the Internet periodically broadcasts the connection relationship between itself and the adjacent router to other routers. Each router on the Internet uses the received route information to draw an Internet topology. Calculate the shortest path to each network by using the drawn topology and shortest path priority algorithm.

OSPF route selection Protocol

Advantages: fast convergence speed, service type selection, and Server Load balancer and identity authentication.

Disadvantages: High router processing capability and bandwidth requirements.

Applicable environment: Internet with a large scale and complex environment

Differences in principles:

Vector-distance routing selection algorithm: you do not need a router to understand the topology of the entire Internet. You can use an adjacent router to understand the possible path to each network.

Link-status routing selection algorithm

It depends on the topology of the entire Internet. The SPF tree is obtained using the topology of the entire Internet, and then the SPF tree generates the route table.