MTU in the router - what is it? Maximum transmission unit. Router settings

Many users of the Internet, for connection to which secure connections from providers are used, can feel discomfort in the work, due to the inability to open some Internet resources. The problem is sometimes solved radically - the router or the provider changes, but there is a high probability of fixing the situation yourself by configuring just one parameter called MTU in the router. What is it, how to find and correctly set up - the questions that are discussed in this article.

Introduction of clarity

To increase the speed of the Internet, packet data is used over the communication channels . After all, it makes no sense to send and receive information on each bit, downloading the channel. Therefore, a technology was created that allows to collect the data stream in a special package, which is transmitted over distances. When the package is received, the destination computer simply unpacks it and receives the original data. In the process of using such a system, limitations were discovered that led to a loss of speed with increasing packet size. Due to this, the corresponding standard was introduced - the maximum transmission package for the equipment (Maximum Transmission Unit), and in short MTU, in the router. That this, of course, remains to identify the reasons for which this standard does not work correctly.

Paranoia or security

Naturally, any standard provides for solving problems in emergency situations. A special fragmentation was developed for MTU, which allowed to change the packet size at a low level at the request of the target computer in the network. The request itself was performed at the TCP transport layer using the ICMP protocol, whose task is to send service messages. Link layer protocols, if they can not receive the packet, send a message about the impossibility of this. The sender reduces the size of the parcel and sends it again. However, this does not always work. After all, very often the Internet resources are managed by very lazy administrators who, instead of making fine-tuning of the security system, go along an easy path, disconnecting, in their opinion, unnecessary protocols. Naturally, ICMP is one of them. And there is no message - there is no problem, the end user, using someone's fault, uses the paid service not in full.

Excellent ping-indicator

And to permanently leave doubts, which settles in the mind of the user technical support of any provider, you need to know the important fact - the ping command is not an indicator. Since its primary task is to check the availability of the resource, but not the quality of the communication channel. You can verify this by yourself by running ping ya.ru on the command line. The response from the destination server will indicate that a 32-byte packet was received. And if you send a packet that is set by the standard of 1500 bytes? The command will look like this: ping ya.ru -f -l 1500. Where l is the size of the package, and f is the prohibition of fragmentation. There may be problems, beginning with the impossibility of acceptance, ending with losses on the channel. Taking into account that all information received from the Internet is transmitted in large packets, it is not advisable to trust the ping command . In this case, the packet size is nothing more than the MTU value, editing of which can improve the Internet performance.

Features of the provider

First of all you need to understand which parameter Maximum Transmission Unit is installed at the provider. If the Internet service is provided by means of a twisted pair cable, without any network settings, there will be no problems. But in cases when using protected PPPoE channels or VPN virtual private networks, you need to be prepared that you can not do without setting up a router and a computer. There are many options for determining the correct size of the package, as well as eliminating the problem, and attention will be paid to several, the most effective methods. Naturally, you can try the provider in the phone mode to figure out the MTU parameter and register it on the router, but it's too simple and, most likely, impossible because of the operator's low competence.

Maybe the problem is different

It is possible that the inaccessibility of some Internet pages does not arise due to incorrect MTU configuration in the router, that this fix does not solve the problem. You need to know exactly in which direction to move. To do this, the user must enter the settings of his router and lower the default MTU to 1400 bytes. After saving and rebooting, try to go to the required resource again. If the problem persists, reset the settings to their original position and start searching for the solution in a different direction. However, according to many users, changing the size of the maximum package to a smaller side gives a positive result and all resources, including online games, are available. However, there is another problem - the speed of opening pages and downloading files is slow. It is required to open the parameters of the router and make fine tuning of the MTU.

From words to deeds

In order to proceed to the settings, it is necessary to enter the address of the router in the address bar of any browser and enter the login and password in the login window. Naturally, if the administrator made an adjustment on the part of the provider, in his competence and the elimination of problems in working with the Internet. But the rest of the users know the password itself and the login to the access point. In any case, without authorization, the problem can not be eliminated, because the parameters of the router will be unavailable.

In the end, there are no desperate situations. You can find out from the network setup provider, reset the router and factory settings and make the connection yourself. In the mass media, there are enough instructions for setting up the necessary hardware, not to mention brand guidebooks from the manufacturer, which can be found on the official websites of the seller.

How to find MTU in a router

The most popular in Russia is the D-Link router, so all fine tuning examples will be described on the basis of its functionality, which is not very different from other routers. Once in the main device setup menu, look at the WAN item in the "Network" section. This item is responsible for building a communication channel between the router and the equipment of the provider, its presence is mandatory in any network device. Once in the right menu, the user can discover several connections that have the status "connected". Preference should be given to the one that has the default gateway flag. Set the cursor to the selected connection. By clicking the "change" button (or "add" - each version has its own names), the user will go to the fine-tuning menu. Find the desired item with the inscription MTU. Change the parameter by clicking on the pencil image in the selected field. Set the desired size. Save the settings and reboot the router.

The correct settings of the router always bear fruit

MTU setup in the router, as practice shows, is key for many channels built on virtual private networks. However, few people know that the fine-tuning of a quality connection depends on two more points that are always near the MTU field. Correct setting of all parameters always solves problems in networks that have physical wear. The router D-Link, Zuxel, Cisco, Linksys and some other devices automatically fill important parameters. In such cases, without much desire to change the parameter is not worth it.

1. Keep Alive. The created virtual network is constantly maintained by the router, from the moment it was turned on until the power was turned off.
2. LCP interval. The parameter is specified in seconds and specifies the frequency of requests from the router to the equipment of the provider to verify the efficiency of the channel.
3. LCP dips. A parameter that allows you to perform a disconnection from the equipment of the provider in order to establish a new, higher-quality communication channel in the event of the non-return of several previously sent packets.

Standards for private networks

If you do not want to experiment on your own, you can use the technical data prescribed in the standards to determine the desired MTU size.

1. PPPoE connection. To each transmitted packet, it attaches its own security data, which it is customary to call the header. This header takes 8 bytes from each packet, leaving the channel able to transmit 1492 bytes. On this technology the work of ADSL is built, accordingly, for tuning modems, MTU change is mandatory.
2. Private VPN and PPP networks. Here MTU is more dependent on the equipment of the server to which the connection is made. After all, in addition to the provider, the connection can be used to connect to the workplace in the enterprise through a remote connection. The parameter of 1400 bytes is considered to be optimal, but fine tuning is not forbidden.

Software to help

You can also determine the required MTU size without experimenting with the router with the help of software. For example, the program TCP Optimizer performs independent calculations on the communication channel and gives the result to the user with a complete description of the problem. Quite convenient, but resource-intensive. After all, the program needs to be found, downloaded, installed and sorted out in its operability. And having understood, any user will find out that the application uses a banal ping of some resource on the Internet. It turns out that you can determine MTU from the command line? For simplicity, you only need to reduce the packet size by one until the server response is positive - ping ya.ru -f -l 1499.

Many software products for setting up networks offer fine tuning by editing the system registry, prescribing special keys for network equipment. Such functionality was in demand in the systems of the last century, however modern operating systems can adapt themselves to the established communication channel and sometimes for efficiency after fine tuning the router it is required to reboot the computer.

Finally

Having received information about MTU in the router, what it is and how to fine-tune the equipment, you can proceed to direct actions aimed at improving the efficiency of the communication channel. However, before you start working, you need to know that not all routers allow you to change their characteristics. For example, the company ZTE, known for its 3G modems, considered that setting up the MTU violates some internal security rules. Accordingly, you can not manually change the required parameters. Experts recommend installing equipment purchased from the provider, or before buying at least agree on the choice with the Internet provider.