How ISPs deploy BGP routing protocols in the network

With the development of the Internet in China, the connection between ISP service providers and Internet is also changing. On a network connection, from a single connection to the Internet via multiple telecommunications companies, in terms of routing protocols used, from the use of static routing protocols to the use of BGP (Border Gateway Protocol). How does the ISP deploy the BGP routing protocol rationally and effectively in the network with the development of the network? We'll give you a brief introduction in this article. In fact, the dominant idea of how to deploy BGP routing protocols in the network is how to make the routers within the autonomous domain acquire autonomous extraterritorial routing information, which can guide the traffic flow out of the autonomous domain.

In general, the following points should be considered in deploying BGP routing protocols within a domain:

1. The actual topological structure of the network;

2. Whether the performance of the device satisfies the requirements for starting BGP, the BGP routing table is usually very large to increase from 50,000 to now about 100,000. The memory and performance requirements of the router are very high;

3. The distribution of the backup and traffic of the line when there are multiple Internet access lines.

The following examples will illustrate these issues in detail. Before proceeding, let us mention a few concepts:

Core layer: A backbone network with high-speed exchange capability, which is located at the core of the network.

Distribution layer: In the periphery of the core layer, it is usually used to implement various routing strategies or implement access control functions.

Access layer: At the outermost level of the network, routers within that range are the access points that users connect to the ISP.

In the initial stage of network development, the network structure is relatively simple (figure I), ISP only one line connected to the Internet. Generally, people do not use BGP in this simple network structure, but use simple and convenient static routes to interconnect. This simplifies router configuration, facilitates management, and reduces performance requirements and costs for border routers.

If you need to enable BGP, it is also simple to enable BGP on the router R1 and R1 as the default gateway for other routers in the network to inject external routes into the network.

With the development of the network, the ISP needs to connect with the Internet through a number of different network providers to ensure the reliability of the network. This is where BGP really comes in. In this case, the following structures typically appear in the network. As shown in figure two, figure three. The two network structures look similar, and the network structure in figure three simply adds a router to exclude the possibility of a single point of failure in the router R1 in Figure II, but it is completely different in how BGP routing is deployed.

In figure II, you simply configure BGP on the R1 and use R1 as the default gateway for other routers in the network and

The BGP routing protocol provides the weight of this routing parameter, which regulates the distribution of traffic in the network on two lines. In this way, we can realize the mutual backup of the line, and can effectively adjust the flow distribution.

In figure three, there are two routers that have external routes, usually in order to ensure the routing consistency within the domain, to establish a IBGP connection between the router R1 and R2 in the graph to establish a consistent BGP routing table. In this process, the local-preference routing parameter provided by BGP routing protocol can be used artificially to optimize routing to control the distribution of data traffic on the line. But how to communicate these external routes to other routers in the network, there are two simple ways to do this: