What does cutover mean in network engineering?

1. Main contents of this article

• What types of business (technology related) does network engineering involve?
• What is Network Cutover?
• Let's take a look at an example of network cutover (without going into technical details)
• What should be paid attention to during network cutover?
• How to write the network cutover document delivery materials

2. About Network Engineering Business

In the network engineering industry, there are many types of business. From a technical perspective (not distinguishing between pre-sales and after-sales), common businesses include:

• Pre-sale testing
• Pre-sales solution consultation
• Network solution feasibility analysis
• Implementation of new projects (such as network construction, etc.)
• Network transformation or expansion, network maintenance
• Troubleshooting
• Software Upgrade
• Technology, project and product training
• Inspection, network security and health status analysis
• On-site service
• other

Therefore, there are many types of technical services in the network engineering industry, which depends on the position, customer requirements, and the company's overall arrangements.

3. Network Cutover

I want to make it clear again that the concept of "network" we are discussing here does not refer to small-scale networks such as small home broadband, but large and medium-sized industrial-level networks, such as enterprises, financial institutions, government agencies, large-scale educational campus networks, etc. For small home networks, you can just tinker with them yourself, and at most you won't be able to access the Internet at home. However, networks for industrial, commercial, and business purposes require professional technical services.

Suppose we have a client who has just built a new campus, which includes several buildings and covers a wide geographical area. We will not talk about the construction of the campus, but after the campus is built, a dedicated network is definitely needed to carry the company's business traffic. It may be wireless, wired, or a wired and wireless converged network. In any case, a large-scale campus network is definitely needed to carry electronic business interaction data. At least, users in the campus always need to go online, right?

If there is a demand for network construction, there will be sales of network products or solutions. Here we will ignore the sales process and assume that all pre-sales and sales processes have been finalized. Then the next step is to implement the new network. After the network is built, generally speaking, there is another part of service delivery, which is to provide customer training. The training content is about the implementation, usage, and maintenance methods of network-related products. Then the network is put into use. During the use process, there may be some small adjustment requirements, such as the addition of VLANs and IP address segments, which is network maintenance. In addition, network failures are inevitable, so fault handling is required.

If the network needs to be transformed, upgraded, migrated, or other changes after running for a period of time, and these network operations occur on a network that is carrying business traffic, then this behavior is called cutover.

Network cutover may be to adjust the network structure, add or replace network equipment, change lines, change equipment configuration, or other changes required for the network.

Network cutover is a relatively difficult operation, especially when dealing with the core networks of operators, finance, government or large enterprises. Every cutover operation needs to be done with great caution, because if the operation fails, the impact will be very bad. Therefore, network cutover has certain requirements on the technology, skills, physical strength, mental strength, experience, etc. of professional engineers.

4. Network Cutover Example

Here we will take a look at a typical case, and we will focus on understanding the network cutover behavior. Before the transformation of a network, the network structure is shown in "Before the transformation". It can be seen that the network structure is relatively simple, and there are defects of a single device and a single link. There is no redundancy in the equipment and links. Then after the network has been running for a period of time, the network may often have problems. For example, if the uplink link of the access switch fails, then the users connected to the entire access switch will not be able to access the Internet.

The customer then proposed a network transformation requirement, with the overall goal being:

• Added new aggregation and core layer equipment;
• All access switches are changed to dual-link uplink to aggregation switches;
• Implement layer 2 and layer 3 redundancy technologies to improve network redundancy and reliability;
• Re-plan the OSPF network model;
• Adjust the data flow direction

This network may have business traffic being forwarded on it at all times, so the cutover operation needs to fully consider this traffic and possible risks, and make full preparations and communicate fully with customers. Try to make the switch as smooth as possible to reduce the impact on the business.

In view of this transformation goal and customer needs, the engineers need to do the following:

• Thoroughly understand the existing network environment, including but not limited to network physical and logical topology; network equipment configuration and related operating parameters; business data flow direction, etc.
• Understand the customer's expectations and needs for the transformation
• Write a network transformation (or cutover) plan based on customer needs. The content of the report will be discussed in the next section.
• In the process of formulating the cutover plan, it is necessary to fully consider the impact of each cutover step on business traffic and consider the fallback plan for each step. Will the network be disconnected? If so, how long will it last? Do you need the cooperation of the customer to issue a notification?
• Submit the written cutover plan to the customer and fully communicate with the customer, and finally determine the cutover plan and cutover time so as to make relevant preparations. Generally speaking, if the cutover action is too large, it is often carried out when the business traffic is small, such as in the middle of the night.
• If necessary, you can also choose a time to do a small-scale test in the existing network.

Therefore, we can see the following characteristics for network cutover:

• This thing requires careful, careful, and careful again
• From a technical perspective, various issues need to be considered. For example, if the routing environment is complex, are there any problems such as routing loops that may occur during and after the cutover process?
• Preparation for cutover is very important
• Cutover often occurs in a network that is already carrying business traffic. In order to reduce the impact of cutover on business, it is usually performed when business traffic is low, such as in the middle of the night or during holidays. Those who work in operator network construction often work in the middle of the night, which is very hard. Therefore, health is very important. Moreover, sometimes a long cutover is performed in the computer room. You know the computer room, so pay attention to insulation measures and bring some bread, which is sometimes necessary.

5. What should be paid attention to in the cutover plan

The plan is just a deliverable of the cutover idea, sometimes it is shown to customers, sometimes it is shown to leaders. Of course, the key is to fully understand the entire cutover process. Generally speaking, a cutover plan will include the following content (of course, it depends on the specific situation):

• Purpose of this document
• Project Background
• Network Existing Networka) Network topologyb) IP, VLAN informationc) Routing and data flowd) Equipment configuration backup
• Cutover target a) Network topology after transformation b) IP and VLAN information c) Routing model d) Data flow e) New device model and version information f) Device management information
• Implementation process a) Step 1: xxxx; (also includes fallback plan, the same below) b) Step 2: c) Step 3: d) Step 4: e)……
• Cutover progress and responsibilities of all parties
• Test environment and scripts
• Other deliverables