MPLS - what is it?

In modern enterprises, when building the infrastructure of a corporate network , MPLS technology can be used. What are its features? What advantages does it have over traditional routing technologies?

General information about the technology

What is the specificity of MPLS? What is this technology? MPLS is a concept in accordance with which the redirection of packets is carried out in computer networks. Its main feature is in the proposal of an alternative to analyzing IPLP-type routers for all packets, which is carried out in order to determine the direction for their forwarding to the next component of the infrastructure. If the technology in question is involved, the header analysis is performed one time at the entrance to the MPLS network, and then the correspondence between the packet parameters and the flow properties is initiated.

Features of MPLS development

MPLS technology was developed by specialists interested in implementing a universal data exchange protocol that would be suitable for both a circuit-switched infrastructure and a packet-based application. In MPLS networks, various kinds of traffic can be transmitted - IP, ATM, Ethernet, SONET, SDH. The concept was developed taking into account the merits and demerits of earlier protocols of a similar purpose. In some aspects, MPLS involves the implementation of simpler algorithms in comparison with the approaches used in traditional solutions. As experts note, network equipment that supports MPLS technology can supplant traditional solutions from the market, which indicates that MPLS developers have done a good job of optimizing and universalizing this concept.

MPLS and IP

So, we know the basic principles of the MPLS concept, what kind of technology it is. In normal networks that use the TCP-IP protocol, packet routing is implemented using the IP address of the computer to which the packet is transferred. On the network, all routers have information about which interface is involved in the data transfer, as well as on which computer the current packet should be redirected to.

In the case of using MPLS, a different approach is implemented. It, as we already know, involves the implementation of switching using labels. They are tied to a specific packet that is sent to the network. Routers, having received it, simultaneously have information about how to transfer data further - based on the specific value that the MPLS-label has. It can be noted that it is located within the MPLS header, placed between the frame and the packet, in accordance with the accepted format. It is noteworthy that several labels can be placed on one package. To indicate that a label is the last one in a group, special flags are used.

It will be useful to consider in more detail the advantages of the technology in question, over traditional solutions.

Key benefits of MPLS: data processing efficiency

The most important advantage of MPLS is that it costs less time to process data than when comparing an IP address. Moreover, MPLS technology reduces the time it takes to redirect a packet using basic routers. In fact, switching can be performed using several protocols, in which special labels are used within packets of transmitted network data. Due to this, separate switched flows are formed.

Advantages of MPLS: Versatility

Another important property of the concept is universality. Virtually any IP MPLS network can be implemented. The technology in question is well supported on the hardware level. In principle, it is possible to use affordable solutions for the introduction of MPLS - Mikrotik, for example. Universal principles of bringing the infrastructure into a working state are universal. However, when designing an MPLS network, the equipment must be set up by experienced specialists. First of all - competent in understanding the features of the network architecture, the characteristics of its hardware components.

MPLS Advantages: Scalability

The MPLS infrastructure is characterized by scalability and a high degree of autonomy with respect to the various protocols through which data is transmitted. Specificity of specific standards implemented at the link level does not matter. When implementing the MPLS network, there is no need to ensure the operation of networks at the second level, which are optimized for the transmission of certain types of traffic. In terms of classifying networks by the type of switching, MPLS can be rightly attributed to the infrastructure in which packet switching occurs.

MPLS Architecture: Basic Devices

We will study what devices are supposed to be used in networks where the MPLS concept is used, what kind of infrastructure it is in terms of applying hardware resources. The main devices that are involved in the relevant technology, you can call:

- Router compatible with the concept of MPLS, as well as with conventional data transfer protocols;

- A router that interacts with devices that do not use label-switching (including for lack of MPLS support);

- A group of network devices that are used for switching using labels in the framework of a common system of administration and routing.

In fact, devices of the first type form the corresponding group, which, in turn, forms a domain. MPLS routers of the second type form the boundary domain of this domain.

Basic principles of MPLS-switching

We will study what is based on what principles the commutation is carried out within the framework of the technology in question. As we already know, the key component of MPLS is a label. Their exchange forms the basis of the corresponding technology. All packets that are transmitted on the network are associated with a specific type of network layer. Each of them is identified with a specific label. Its value is unique only when viewed within a particular section of the path, which lies between the nodes of the network located in the neighborhood, that is, the first type of routers (according to the classification we discussed above). Any package will thus include a label. However, the way it is associated with the package will depend on what technology is used within the network infrastructure.

Communication between routers

A particular router can request network information using some algorithm compatible with MPLS-BGP, for example. The main function of the device in this case is to provide data exchange with neighboring devices through the distribution of labels subsequently used for switching purposes. They can be exchanged directly in different ways. For example, the LDP protocol may be used, or modified versions of other routing standards used by the network administrator.

Component table

In the process of label distribution, different data paths are formed in the communication of different devices. Each of the routers in use uses a table that ensures that the components associated with the input interface match those that reflect the characteristics of the output infrastructure. The router, having received this or that packet according to the interface number, and also having read the value of the label, sets the specified output interface for the transmitted data. At the same time, the previous value within the label is corrected and replaced by a new one, which is reflected in the part of the table where the output tags are fixed, after which the packet is directed to another element of the network infrastructure.

The MPLS protocol assumes a one-time identification of individual field values located in one row of the table used. IP-адрес исходного устройства имеет самый длинный префикс в рамках таблицы маршрутизации. This is the reason for the fact that the concept under consideration allows for more rapid data transfer in comparison with the methods used in normal routing when the IP address of the source device has the longest prefix within the routing table.

Structure of MPLS

Let us consider in more detail the peculiarities of the structure of the network concept in question. MPLS consists of two main components:

- the core;

- the border area.

In the kernel structure there are devices that necessarily support MPLS. They are used as infrastructure components for routing traffic within a switched protocol. Thus, the main function of the devices present in the core is switching.

In turn, the border area responds: for classification of packages according to established criteria, for the implementation of related services - for example, related to filtering during data transmission, for managing network traffic. This distribution of functions between the core and the border area allows you to configure the MPLS network taking into account the specific location of specific devices within the network.

Ways of marking packages

Let's study in more detail how the marking of data packets using MPLS-tags is carried out. First of all, it should be noted that the label has the following main characteristics: fixed length, unique in the context of a separate connection that is carried out between neighboring routers.

In fact, a label with the same value can be used on different parts of the network, but only within the communication between individual pairs of routers. True, in this case, the devices must determine exactly where the data packet marked with the appropriate label came from. In practice, the simplest network connections can use the same set of MPLS tags within the interface.

In more complex infrastructures, it is proposed to use a separate set of labels within a single module or device. Just before they are included in the package, the MPLS-label is coded according to the established algorithm. If the network uses the IP protocol, the label is placed within the header of the packet. In other cases, it is reflected in the header of the protocol already at the link level. It can also be encoded in a specific meaning.

Using Label Groups

In the process of data transfer using the network concept under consideration, in the packet structure, there may be, as noted above, a group of labels-stacks. In each of them, the operation of adding or removing one or more labels may be reflected. In this case, only the topmost one sets the specific switching result. This feature of data transmission in MPLS networks allows to implement tunnel communications. There are components on the stack that have a length of 32 bits. At that 20 is allocated to the label, 8 - to the counter of the period of the packet's life, 1 - reflects the lower limit in the tag group, 3 - are not used in practice. In general, any value of the label is possible, excluding some reserved ones.

The structure of the switched path

In order to understand in detail the principles of the MPLS network, what kind of technology it is, it will be useful to study the features of the structure of the switched path that is built within the network infrastructure. Its main feature is that it consists of a set of sites - on one level. They are switched using labels at a specific level.

In the structure of a given level, the use of an input and output router is assumed. Above, we noted that MPLS can use the LDP protocol. Let's study how the dial-up path can be built using LDP.

First of all during the distribution of UDP packets, at which a large number of addresses can be used, routers establish their own location on the network - using LDP. Also, communication can be defined between routers that do not belong to the same channel. This feature of the network structure is important from the point of view of implementing data transmission in the tunnel format.

After the location of the routers is established, the LDP protocol starts the connection outside TCP, that is, over it. In the framework of it, requests to initiate the binding, as well as information about it, are formed. Test messages can also be sent between different devices to verify the health of the network.