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CCIE Network engineer must know :In-depth analysis of redundancy, symmetry and load balancing

CCIE Network engineer must know :In-depth analysis of redundancy, symmetry and load balancing

Redundancy, symmetry, and load balancing are the key issues that every network engineer must face. Operators and their customers need to fully control the flow of traffic in and out of their respective ASs. Let’s first understand their related concepts. redundancy:

Regardless of which company or provider is unwilling to see its own network interruption, network connectivity problems will always come up for one reason or another. The problem of connectivity depends on many factors. A link to the Internet will involve routers, CSU/DSU, power supplies, cable connections, physical access lines, and many O&M personnel-each factor will affect the link differently. At any time, human error, hardware and software failures or natural disasters may cause network interruption. Because of this, redundancy is indispensable to the network. However, the most critical thing is to find a balance between redundancy and symmetry. In terms of network design, redundancy and symmetry seem to be natural enemies: the higher the degree of network redundancy, the more unpredictable the in and out points of traffic.

For a network, redundancy refers to a link that can transfer incoming and outgoing traffic in addition to the active link, which translates into additional routing information that needs to be stored in the routing table. When the main link fails, we can open the backup link for us.


Symmetry refers to the traffic sent from a given exit point, and the feedback traffic can also return from the same point. If the AS has only one flow entrance and exit, then flow symmetry is a natural thing. However, when redundancy is required and there are multiple paths, traffic always tends to be asymmetric. Once the traffic is asymmetric, both the provider and the customer will find it impossible to effectively control the traffic to and from the AS. In fact, traffic asymmetry can be acceptable in some cases, depending on the applications running and the overall physical network topology. Generally speaking, customers and providers want to leave the AS traffic, and their feedback traffic can return from the point close to the exit point or from the origin, in order to minimize the potential delay caused by unexpected circumstances. Furthermore, customers will also allow traffic to travel as long as possible within the local network to avoid delays and congestion in peer-to-peer networks. In order to achieve traffic symmetry, it is necessary to define a primary link, and try to let most traffic be transmitted on this link.

Load balancing:

Load balancing refers to the ability of multiple links to share data traffic. A common misunderstanding is to equate it to an even distribution of load. Even if the network carrying traffic is managed by a single entity, it is rare to evenly distribute the load. In the vast majority of scenarios, the traffic has to change hands many times along the way, and the even distribution of traffic becomes even more difficult. Load balancing is intended to efficiently use multiple links that are deployed for redundancy to achieve a traffic distribution pattern. To achieve this model, it is necessary to understand the required load-balanced traffic, and pay attention to both the flow of people and the flow of outflow. Traffic should be divided into two-inbound traffic and outbound traffic. For autonomous systems, inbound traffic is traffic received from other ASs, and outbound traffic is traffic to be sent to other ASs.

Load balancing is divided into hardware and software load balancing and local global load balancing.

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Software load balancing solution refers to the installation of one or more additional software on the corresponding operating system of one or more servers to achieve load balancing. Its advantages are based on a specific environment, simple configuration, flexible use, low cost, and can meet General load balancing needs.

The hardware load balancing solution is to install a load balancing device directly between the server and the external network. This type of device is usually called a load balancer. Due to the special equipment that completes specific tasks and is independent of the operating system, the overall performance has been greatly improved. Diversified load balancing strategies can achieve the best load balancing requirements.

Local load balancing does not require a high cost to purchase a high-performance server. It only needs to use existing equipment resources to effectively avoid the loss of data traffic caused by a single point of failure of the server. It is usually used to solve the problem of excessive data traffic and heavy network load. problem.

Global load balancing mainly solves the problem that global users only need a domain name or IP address to access the server closest to them to obtain the fastest access speed. It has its own server site in multiple regions, and it is also suitable for those subsidiary sites. Large, widely distributed companies meet the needs of rational resource allocation through the corporate intranet.

On the Internet, collaboration between multiple entities is the way to balance traffic. How to maximize redundancy, symmetry and load balancing is an eternal design problem for every network. However, the specific solution depends on the configuration and needs of each specific network.

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