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Overview of routing policy - The first routing strategy-1

2018-02-05 13:39:36

For IP network engineers, the deployment of routing strategies can be seen everywhere. The application of routing strategy is very common in operators IP network or enterprise network. At the same time, in network planning, the planning of routing strategy is also a core content. In order to help you better grasp and apply the routing strategy, we launched the topic of routing strategy. I hope this topic can help you to discuss and learn together.

1 routing strategy overview

1.1 what is the routing strategy?

We generally talk about something that can't avoid such a question: "what is XXX?" Here we also try to define a routing strategy to answer: "what is the routing policy?" This is the problem.

Many people will equate the routing strategy to route-policy. Some people may say that filter-policy is also a category of routing strategy. Actually, these understandings are not very accurate. In fact, routing policy is not a specific technology, nor is it a specific feature.

A routing strategy is a "strategy" for various kinds of control through a series of tools or methods. This strategy can affect routing, release, and selection, and then affect the forwarding path of the message. These tools include ACL, route-policy, ip-prefix, filter-policy, and so on, which include routing filtering, setting routing properties, and so on.

1.2 The call relationship between the various tools of the routing policy

When discussing the routing strategy, we often encounter many kinds of tools, such as ACL, route-policy, ip-prefix, filter-policy and so on. A lot of people will be they call the relationship between confused, always feel that the relationship between them daobuming. Here we are going to give you a picture of the relationship between them.


Figure 1 call relations between the various tools of the routing policy

As shown in Figure 1, we divide all the tools into three categories:

L condition tool: used to "grab" the required routing.

L policy tool: used to carry out the "grab" route to perform a certain action, such as allowing, rejecting, modifying property values, and so on.

The L invoking tool is used to apply routing policies to a specific routing protocol to take effect.

The filter-policy and peer in the calling tool are also equipped with the function of the policy tool, so these two things can call the conditional tools directly. The other invoking tools have to invoke the conditional tools indirectly through route-policy.

It is important to note that peer cannot call ACL and can call all the other conditional tools.

1.3 What is the use of the routing policy?

In the IP network, the use of routing strategy mainly includes two aspects: 1) filtering the routing information. 2) modify the properties of the routing. Please see Table 1 in detail.


Execution process


Filtering routing information

If a route conformsXXConditions, then receive this route

If a route conformsXXConditions, then publish this route

If a route conformsXXConditions, then this route is introduced


Modifying the properties of the routing

If a route conformsXXConditions, then the value of an attribute of this route is modified to beXXX

Some attribute value of this route isXXX

Table 1 routing strategy

If you feel that the introduction of routing strategy is still a little abstract, it doesn't matter. Let's introduce a real example to you.

Routing information filtering through routing strategy


Figure 1 filtering routing information through a routing strategy

As shown in Figure 1, SwitchA belongs to a dual uplink network structure, and SwitchA receives routes from SwitchB and SwitchC respectively. What if SwitchA only wants to receive routing from SwitchB and does not want to receive routing from SwitchC? In this case, you can consider configuring routing policies on SwitchA, allowing routing from SwitchB, and refusing routing from SwitchC.

Modifying the routing properties by routing policy


Figure 2 modify the routing properties by routing policy

As shown in Figure 2, the network structure, SwitchA is upward but due to better link stability SwitchB here a little, a little more bandwidth, so users want to use this as the main link SwitchB link, SwitchC side of the link as a backup link, when the main chain fault when the flow switch to the standby link. In this scenario, you can use the routing strategy, the routing overhead from the SwitchB side of the small value, will come from the SwitchC side of the value increase the routing overhead, so the flow will automatically select the SwitchB side of the link with the SwitchC as the main side of the link as a backup link, realize the main backup routing.

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