Unlocking the mystery of redundant routing automatic switching in Broadband Access Networks

Broadband Access Network is a commonly used access method. At the same time, we may encounter many problems, such as the failure to automatically switch redundant routes. Many people may not understand the causes and solutions of such problems, it doesn't matter. After reading this article, you will certainly have a lot of GAINS. I hope this article will teach you more things. A broadband access network server is installed at a node in the convergence layer of a certain technology network. The number of users connected to the network is very large at ordinary times. To ensure the stability of the access connection, the network uses a dual-line connection to connect the broadband access network server to two core switch devices. The dual-connection line uses a gigabit fiber link, and the network route uses a Static Routing addressing method. During the construction of the network, considering that the user access traffic is relatively large under normal conditions, in order to effectively share the traffic, the network uses two Gigabit Optical Fiber Links to achieve load balancing: when one of the Gigabit Optical Fiber Links fails to work normally or its winding switch is faulty, all bandwidth access traffic should be automatically switched to another Gigabit Optical Fiber Link, so as to achieve the purpose of redundant routing protection, so as to ensure that broadband Internet users can always access the Internet normally. After the networking construction task is completed, the debugging results meet the established construction requirements.

Automatic Switch fails in the first time

Recently, many Internet users who access the technology network through broadband access network servers have reported that the current Internet access speed is obviously not as normal as before. They opened a common page that does not contain images or multimedia information, it also takes a long time to complete. When you use the ping command to test the address of the target website, the data packet loss rate is found to be very serious, sometimes reaching 50%, obviously, this broadband access network has obvious faults. To quickly identify the cause of the failure, the network administrator immediately uses the telnet command to remotely log on to the background management interface of the core switch device for detailed checks, the result shows that the Gigabit Optical fiber link connecting the Broadband Access Server to one of the core router devices has been down, however, at this time, the network route is not automatically switched from the faulty fiber link to the working fiber link. It is no wonder that there is 50% data packet loss in broadband access.

Cannot automatically switch

To ensure that broadband access users can access the technology network quickly and normally, the network administrator has to adjust the Routing Parameters in the core device to reduce the priority of static route access related to the faulty communication link, make sure that the network route can pass through another optical fiber link in normal working status. After modifying the parameters, the broadband access network user can access the network normally.

Later, the network administrator deliberately simulated the actual working environment of the Technology Network, set up a switch device, and achieved the goal of connecting switches on two-line roads through the backup optical fiber link, set a static route on the two core switch devices to connect to the new switch, at the same time, set the working status of the switch interconnection port connected to the faulty optical fiber link to "shutdown", and then check the corresponding Routing Status on the newly established switch, the Network Administrator finds that it is also in the down state, and the core switch connected to the faulty Optical Fiber Link, although the virtual working subnet under the corresponding Switch Connection port has been down, however, the static route record of the newly established switch still exists.

After checking the configuration parameters of the core switch device in detail, the network administrator finds that the core switch device used in the local technology network is significantly different from the technology network in other places, after the network adjustment between the Provincial Science and Technology Network and the provincial Telecom, the core switch equipment of the local science and technology network is directly connected to the high-end router of the local telecom network, and the core switch device is connected to the router that runs the BGP protocol, the record content in the local route table is directly introduced to the nearest node through the network. However, when attempting to introduce a local route record through the network, it must exist in the routing table beforehand. Otherwise, it cannot be introduced normally. But in fact, there are only some specific routing records in the routing table, but no aggregation route records. Therefore, the network administrator specially sets a route to the null0 exchange interface to spoof the Border Gateway Protocol, thus using network configuration, this allows the VBR to successfully introduce the aggregated route records.

At this time, the failure is completely apparent. When a fiber link in the convergence layer of the Technology Network suddenly breaks down, A static route record in a router running the BGP protocol to null0 is always in the up active state, and the static route has a higher access priority than other routes, therefore, there will always be a static route record connecting to null0 on the core switch device connected to the faulty optical fiber link. In the early stage, the broadband access network transformation project test happened just before the network adjustment between the Provincial Science and Technology Network and the provincial Telecom. At that time, there was no static route record to null0, so at that time, the test results showed that everything was normal.

Because the access priority of static routes is the highest among all routes, with this in mind, the network administrator immediately modifies the Routing Parameters in the core switch device, the priority level for access to the static routes connecting to null0 is slightly reduced. In this way, when a fiber link in the convergence layer of the Technology Network suddenly breaks down, the core switch device on the Link can automatically learn from another core switch device through the OSPF routing protocol. After the task of adjusting the access priority of a static route to null0 is completed, the network administrator performs a test again and finds that the redundant route is automatically switched, the fault has been successfully solved.

Summary

In the process of configuring the vertical network between similar technology systems, it is easy to see that the network configurations affect each other, however, the impact of these phenomena on the network operation in a certain period of time cannot be seen for the moment, which also reminds the network administrators that once some adjustments occur in the network, we should test some key broadband access network projects in a timely manner to ensure that hidden problems in the network can be exposed to the maximum extent, so as to conduct targeted research and solution.

1. First step in building broadband access to China Telecom
2. Discussion on the Development Trend of optical fiber access technology
3. Optical fiber access technology learning notes
4. Development History and prospects of broadband wireless access technology
5. Full solution to Access Network