ProductsBackup Center Technology White Paper
Abstract: This manual mainly introduces the implementation and application scenarios of the backup center.
Acronyms:
Acronym | Full spelling |
BC | Backup Center |
IB | Interface Backup |
Table of Contents
2 Backup Center Implementation. 3
3.1 Interface Backup Application. 7
3.2 Load Balancing Application. 8
1 Overview
The backup center functions to provide backup for the interfaces on a network device. It delivers reliability by switching traffic over to a backup interface when the one that is backed up cannot transmit data because of interface failure or insufficient bandwidth.
2 Backup Center Implementation
2.1 Concepts
l Main interface: Main interfaces are those taking on data transmission and those are backed up.
l Backup interface: Backup interfaces are those functioning as backups for main interfaces. They are generally in the state of STANDBY and do not take on data transmission.
l Priority: You can configure a priority for a backup interface when configuring the backup interface. In interface backup mode, the backup center brings up the backup interfaces based on their priorities; in load balancing mode, the backup center brings up and shuts down the backup interfaces based on their priorities.
2.2 Mechanism
The backup center works in the following two ways:
l Interface backup: When the main interface cannot transmit data because of interface failure, the backup interface with the highest priority will take the main interface instead and take on all traffic transmission. Only one interface can transmit data at any time.
l Load balancing: When the traffic on the main interface increases above the predefined upper threshold, the backup center brings up the highest-priority backup interface, and then other backup interfaces in decreasing interface priority order.
Adopting interface backup or load balancing mode depending on whether you have configured an upper and lower threshold for the main interface traffic. As long as the thresholds are configured, the load balancing mode is adopted; otherwise, the interface backup mode is adopted. Note that these two modes cannot take effect at the same time: In interface backup mode, even if the main interface traffic exceeds the predefined threshold, the backup center will not bring up the backup interfaces to share load with the main interface; in load balancing mode, even if the main interface cannot transmit data, the backup center will not bring up the backup interfaces to take on the responsibility of the main interface.
The following sections introduce the two working modes in detail.
2.2.1 Interface Backup
The backup center is aware of the changes of the network layer status of the main interface and the backup interfaces:
(1) When the network layer status of the main interface is down and this state keeps for a period of time, which is configurable, the backup center starts the backup interface with the highest priority, and sets it to the non-STANDBY state. Then the backup interface starts to establish a connection with the peer; if in a certain period of time, the network layer status of the backup interface is still not up, the backup interface with a priority ranking the second is started. This process continues and the backup center stops starting the rest backup interfaces until the network layer status of a backup interface is up.
(2) Then, when the network layer status of the main interface is up and this state keeps for a period of time, which is configurable, the backup center terminates the connection on the backup interface that has been brought up, and changes its state to STANDBY; if in this period of time, the main interface cannot transmit data because of network flapping, the backup interface will keep its connection with the peer, thus ensuring that the main interface can transmit data normally in network flapping.
As shown in Figure 1 , Router A and Router B connect to each other through Link 1, Link 2, and Link 3. Serial 2/1 on Router A acts as the main interface, Serial 2/2 and Serial 2/3 act as the backup interfaces of Serial 2/1, and the priority of Serial 2/2 is higher than that of Serial 2/3. Serial 2/2 and Serial 2/3 are in the STANDBY state, and Link 2 and Link 3 do not participate in data transmission.
Figure 1 The main interface transmits data in interface backup mode
As shown in Figure 2 , if Link 1 on the main interface Serial 2/1 fails, the backup center brings up the backup interface Serial 2/2 with the highest priority (suppose Link 2 works normally at this time), thus ensuring uninterrupted data transmission between Router A and Router B. In this case, Serial 2/3 is still in the STANDBY state and does not participate in data transmission.
Figure 2 The backup interface transmits data in interface backup mode
After Link 1 recovers, data transmission will restore to the state as shown in Figure 1 , that is, Link 1 transmits data and Link 2 stops data transmission.
2.2.2 Load Balancing
In load balancing mode, the backup center decides whether to bring up a backup interface based on the traffic on the main interface. You can set an upper threshold and a lower threshold on the main interface. The backup center detects the traffic on the main interface at certain intervals (configurable):
(1) When the traffic on the main interface increases above the predefined upper threshold, the backup center brings up the highest-priority backup interface to share load with the main interface. If after this, the traffic on the main interface is still above the upper threshold, the backup interface with the highest priority among the rest backup interfaces is brought up. This process continues until all the backup interfaces are brought up.
(2) During the load balancing process, when the traffic on the main interface decreases below the predefined lower threshold, the backup center shuts down the lowest-priority backup interface. If after this, the traffic on the main interface is still below the lower threshold, the backup interface with the lowest priority among the rest backup interfaces that have been brought up is shut down. This process continues until all the backup interfaces that have been brought up are shut down.
As shown in Figure 3 , Router A and Router B connect to each other through Link 1, Link 2, and Link 3. Serial 2/1 on Router A acts as the main interface, Serial 2/2 and Serial 2/3 act as the backup interfaces of Serial 2/1, and the backup priority of Serial 2/2 is higher than that of Serial 2/3. Serial 2/2 and Serial 2/3 are in the STANDBY state, and Link 2 and Link 3 do not participate in data transmission.
Figure 3 The main interface transmits data in load balancing mode
When the traffic on Link 1 increases above the predefined upper threshold, the backup center brings up the highest-priority backup interface Serial 2/2, making Link 2 share load with Link 1. If the traffic on Link 1 is below the lower threshold after Serial 2/2 is brought up, Serial 2/3 keeps in the STANDBY state, and does not participate in data transmission, as shown in Figure 4 .
When the traffic on Link 1 is lower than the lower threshold, the data transmission recovers to the state as shown in Figure 3 , that is, the backup interface Serial 2/2 that has been brought up is shut down and Link 2 stops data transmission.
3 Application Scenarios
3.1 Interface Backup Application
You can use this function to provide interface backup, thus enhancing data transmission reliability. When the main interface fails to transmit data, the backup center automatically brings up the backup interface with the highest priority.
Figure 5 Network diagram for interface backup
As shown in Figure 5 , Router A exchanges data with the Internet through its main interface Ethernet 1/1; Ethernet 1/2 through Ethernet 1/4 are the backup interfaces, with their priority in descending order. When the main interface fails, the backup center brings up the backup interface Ethernet1/2 with the highest priority; if Ethernet1/2 cannot establish a connection with the peer, the backup center brings up the backup interface Ethernet1/3 with a priority ranking the second. This process continues until a backup interface establishes a connection with the peer successfully, enabling uninterrupted data transmission between Router A and the Internet. When the main interface recovers, the backup center switches the data transmission back to the main interface.
3.2 Load Balancing Application
You can use this function to provide load balancing among multiple interfaces. When the traffic on the main interface increases above a predefined upper threshold, the backup center automatically brings up the backup interface with the highest priority to share load with the main interface.
Figure 6 Network diagram for load balancing
As shown in Figure 6 , Router A exchanges data with Router B through its main interface Serial 2/1; Async 5/1 and Async 5/2 are the backup interfaces of Serial 2/1, with the priority of Async 5/1 higher than that of Async 5/2. The backup center periodically monitors the traffic on the main interface: When the traffic on the main interface increases above the predefined upper threshold, the backup center brings up the highest-priority backup interface Async 5/1 to share load with Serial 2/1. If the traffic on the main interface is still above the upper threshold, the backup center will bring up the backup interface Async 5/2 with a priority ranking the second. When the traffic on the main interface is lower than the predefined lower threshold, the backup center shuts down the backup interface Async 5/2 with the lowest priority; if after this, the traffic on the main interface is still lower than the lower threshold, the backup center will shut down the backup interface Async 5/1 with a priority ranking the last but one.
Copyright ©2008 Hangzhou H3C Technologies Co., Ltd. All rights reserved.
No part of this manual may be reproduced or transmitted in any form or by any means without prior written consent of Hangzhou H3C Technologies Co., Ltd.
The information in this document is subject to change without notice.
