The vision of a fault-tolerant, reliable, scalable data network
Encouraged by the philosophy of network technologies, data transfer technologies, and generally everything that explains how everything works, I decide to write a number of articles about what is a benchmark of network solutions, quality implementation or tuning, or something similar, but presently present and terribly annoying.
In the vision of building networks of Cisco, there is the concept of a three-tier model.
The three-level network model is a hierarchical structure of data transmission not in terms of protocols or models (such as OSI or TCP / IP models), but in terms of the functioning of abstract network elements.
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From the title it is obvious that all elements of the network are divided into three so-called levels. This division allows building fault-tolerant, reliable, scalable data networks. The role of levels is rather logical, and there is no need to physically bind to specific equipment.
It is the core of the network. The only thing he has to do is redirect packets from one segment to another with lightning speed. The base layer is responsible only for high-speed switching of traffic, it is not responsible for routing. Based on this, the basic level must be provided with a high degree of fault tolerance and reliability. Usually duplicate devices operating at a basic level. Consider, for example, Cisco WS-C6503-E .
It is perfect for implementing the core network level. To ensure fault tolerance and reliability, for example, we duplicate it with one more and link so that every device knows at any time about the configuration and topology of the network. If one of the cores fails, or if the transmission medium is unavailable from the level of distribution to one of the cores, the second responsibility will take over the second! I will cite some of the features and recommendations for designing a basic level, which distinguish leading manufacturers of network equipment.
Some features of the base level:
A few guidelines for network design at a basic level:
It is a “layer” between the access level and the core level (base level). It is at this level that the control over network data transfer is exercised. You can also create broadcast domains, create VLANs, if necessary, as well as implement various policies (security and management). At the distribution level, a rule can be applied to the kernel level. I will give some features and recommendations for the design of the distribution level, which distinguish the leading manufacturers of network equipment.
A few recommendations for network design at the distribution level:
The lowest level of the three-level model. The access level contains devices that allow workgroups and users to work with services provided by the kernel level and distribution level. At the access level, you can organize collision domains using hubs, repeaters or switches. With regard to the level of access you can not use powerful equipment, which is used at the levels above. I will give some features and recommendations when designing the access level, which distinguish the leading manufacturers of network equipment.
Some features of the access level:
A few guidelines for network design at the access level:
As I mentioned earlier, the levels of the Cisco three-tier model are not tied to the hardware, but are only logically conditioned. Accordingly, it is sometimes possible to combine the access level and the distribution level in a single device. For example, in a Cisco WS-C3560-4Gig-48PS device you can do this. But it is worth remembering that the merging of these two levels is carried out only because the hardware and software allow you to do this. In fact, two independent logical levels will be implemented in one device.
It is necessary to adhere to the rule when building a network so that the functions of one level do not fulfill the other and vice versa.
Naturally, such a model is acceptable for a network of a large enterprise, in the interests of which its functioning properly. It is necessary to spend a lot of effort and time and money to develop a project, implement and maintain such a network. But it is worth it!
What is it this time ...
In the vision of building networks of Cisco, there is the concept of a three-tier model.
The three-level network model is a hierarchical structure of data transmission not in terms of protocols or models (such as OSI or TCP / IP models), but in terms of the functioning of abstract network elements.
')
From the title it is obvious that all elements of the network are divided into three so-called levels. This division allows building fault-tolerant, reliable, scalable data networks. The role of levels is rather logical, and there is no need to physically bind to specific equipment.
Core Layer
It is the core of the network. The only thing he has to do is redirect packets from one segment to another with lightning speed. The base layer is responsible only for high-speed switching of traffic, it is not responsible for routing. Based on this, the basic level must be provided with a high degree of fault tolerance and reliability. Usually duplicate devices operating at a basic level. Consider, for example, Cisco WS-C6503-E .
It is perfect for implementing the core network level. To ensure fault tolerance and reliability, for example, we duplicate it with one more and link so that every device knows at any time about the configuration and topology of the network. If one of the cores fails, or if the transmission medium is unavailable from the level of distribution to one of the cores, the second responsibility will take over the second! I will cite some of the features and recommendations for designing a basic level, which distinguish leading manufacturers of network equipment.
Some features of the base level:
- High speed data transfer is very important at this level. One of the ways to achieve a high transfer rate is load sharing, when traffic can pass through various network connections.
- When designing you need to take into account the growth of the network. In this case, the base level should not be restructured (expanded). If there are performance problems at a basic level, it is better to choose an upgrade, not an extension.
- Low latency when transmitting packets. Kernel-level devices typically use electronic circuits characterized by a high transmission rate and low transmission delay times. Also, the transfer of data does not comply with the implementation of various kinds of policies. Traffic should be transmitted at lightning speed.
A few guidelines for network design at a basic level:
- Provide high reliability. It is recommended to use data link technologies to provide speed and redundancy (for example, use FDDI, Fast Ethernet with redundant connections or ATM).
- At the basic level, a minimum delay is required.
- Protection from NSD. At failure of devices of level of a kernel.
Distribution Layer
It is a “layer” between the access level and the core level (base level). It is at this level that the control over network data transfer is exercised. You can also create broadcast domains, create VLANs, if necessary, as well as implement various policies (security and management). At the distribution level, a rule can be applied to the kernel level. I will give some features and recommendations for the design of the distribution level, which distinguish the leading manufacturers of network equipment.
- QoS. Routers or Layer 3 switches can prioritize packets according to a set of rules.
- Packet filtering (firewalling). Regulation of packet transmission and transmission based on the extraction of information about where it is from and where it should be sent. In this way inter-network boundaries are created.
- Routing between VLANs and other workgroup support functions.
- Broadcast and multicast control.
- "Sluicing". The distribution level allows you to create “gateway” rules from and to different networks with different topologies.
A few recommendations for network design at the distribution level:
- When designing you need to take into account the fact of further growth of the network.
- When designing, it is necessary to consider the probability of failure of the transmission medium to the base level, therefore it is necessary to ensure redundancy of links to the base level
- Protection from NSD. If the kernel-level devices fail, the network will function within the local subnets; when the distribution-level devices fail, the workstations will not get access to the local subnets.
Access Level
The lowest level of the three-level model. The access level contains devices that allow workgroups and users to work with services provided by the kernel level and distribution level. At the access level, you can organize collision domains using hubs, repeaters or switches. With regard to the level of access you can not use powerful equipment, which is used at the levels above. I will give some features and recommendations when designing the access level, which distinguish the leading manufacturers of network equipment.
Some features of the access level:
- Collision Domain Formation
- You can enable filtering by MAC addresses (configure the switch so that it allows only certain devices to pass traffic to the network)
A few guidelines for network design at the access level:
- Local traffic must remain local
- When designing you need to take into account the fact of further growth of the network.
As I mentioned earlier, the levels of the Cisco three-tier model are not tied to the hardware, but are only logically conditioned. Accordingly, it is sometimes possible to combine the access level and the distribution level in a single device. For example, in a Cisco WS-C3560-4Gig-48PS device you can do this. But it is worth remembering that the merging of these two levels is carried out only because the hardware and software allow you to do this. In fact, two independent logical levels will be implemented in one device.
Important!
It is necessary to adhere to the rule when building a network so that the functions of one level do not fulfill the other and vice versa.
Naturally, such a model is acceptable for a network of a large enterprise, in the interests of which its functioning properly. It is necessary to spend a lot of effort and time and money to develop a project, implement and maintain such a network. But it is worth it!
Source: https://habr.com/ru/post/93629/
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