Introduction to MTU

What is the MTU?
The Maximum Transmission Unit (MTU) (maximum size of the transfer unit) is a parameter that determines the longest datagram can be transmitted by an IP interface without the need to be broken into smaller units. The MTU should be larger than the datagram great that you want to convey without being fragmented. (Put simply, the MTU defines the maximum size (in bytes) of the package can be transmitted at once.)
For Ethernet, this value should be 1500 bytes.For PPPoE connections, 1492For the CTS (low-speed), 576Calculate MTU
Each transmission frame is defined by the body (MMS = = maximum segment size), which defined the largest segment of TCP information can be transmitted, and the header (header in English).Either MSS MTU = + TCP / IP headersConsider:
MSS-40 = MTU <- 40 for the header (20 byte IP and TCP 20 byte)Packages are not brokenNot lost packets
Package size / speedEither the transfer of information of 1500000 bytes using different size packages through a T1 line (rtc) (T1 = 1544000 bits / sec) following formula:
(MSS + header) * 8 bits / byte———————————- Latency =1,544,000 bits / sec.
By using different values of MTU, it is possible to calculate the latency of transmission:
If MTU = 1500, then: (1460 +40) * 8 / 1544000 = 7,772 msIf MTU = 576, then: (536 +40) * 8 / 1544000 = 2,924 msAt 10 laps, you get 77.72 ms for MTU to 1500, and 29.24 for 576 ms.
To summarize, more packages there, the longer is the transfer
Use the same formula for the transfer of 1mb.
1MByte KB = 1024 = 1,048,576 bytes.
If MTU = 1500, then: (1460 +40) * 8 / 1544000 = 7,772 ms1 MByte / MSS = 1048576 bytes / 1460 = 718.2, 719 packages therefore to transfer 1 MByte.
Soi, to transfer 1Mbyte: 719 * 7,772 packets ms (always buckle) = 5588,068 ms, or 5,588 seconds.
If we shifted our 1 MByte of 10 laps (defined by the entete), we will ideally:
(1 package * 10 * 7.772ms delay loops) + 718 * 7,772 = 5,658 seconds.
If MTU = 576, then: (536 +40) * 8 / 1544000 = 2,924 ms1 MByte / MSS = 1048576 bytes / 536 = 1956.3, therefore 1957 packages to transfer 1 MByte.
To transfer 1 MByte: 1957 * 2,924 packets ms (always buckle) = 5722,268 ms, or 5,722 seconds per loop.If we transferred these 1 MByte of 10 laps:(1 package * 10 * loops 2.924ms) + 1956 * 2,924 = 5,748 sec.
The difference is that the larger package is much less that of the header is high (relatively ^ ^)So to transfer 1Mbyte if one uses an MTU in 1500 then there is 719 * 40 = 28760 bytes for entete, while the MTU to 576, we get 1957 * 40 = 78280, or more than 49520 bytes d ‘entete transmitted each Mbyte. For our example of 10 laps, it is not significant, but on transfers daily …
In addition, most modems use a entete most important, and that we do not take into account and such other latencies might be involved.Find the value of MTU under Windows
To find the maximum value MTU, it is necessary to go to the command prompt (Start> Run> “cmd”). Once at the command prompt (page black background), it is necessary to make a ping test, indicating the packet size test:
Ping-f-l (size of the package -2 (IP your server)The-f option allows you to the test by forcing routers encountered not to fragment the packet- L option sends the size of the packageIt removes 28 to the size of the package to test corresponds to the top of this packageWe must take the test to an IP. For the sake of Internet navigation, it’s best to take a web address.
This gives:F ping-l 1372 192.168.0.1– If the answer to requette is:Response 192.168.0.1: bytes = 1372 ….Response 192.168.0.1: bytes = 1372 ….Response 192.168.0.1: bytes = 1372 ….Response 192.168.0.1: bytes = 1372 ….
Here, the size of the package allows for transport without fragmentation, we can try a higher value. When we get the message: “The package has to be fragmented, but set DF”, the size of the package is too large.Changing the MTU under Windows
Once you have determined the optimal MTU, there are two ways to change the value of MTU. I mention here the easiest to implement, Dr software via TCP: http://www.sos-adsl.com/modules/mydownloads/singlefile.php?lid=72
Once installed, you have a case “MTU”, or it is necessary to specify the value found in the test under DOS by adding 28 for entete.
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LAN and Internet Connection Sharing
Posted on April 23, 2008 by salahsamy
I. Configure a network between 2 PC only
You must have a network card installed on each PC! Connect cards with a crossover network cable type RJ 45, and verify that the diodes in the back of the NIC turn! 1. With Windows XPGo to the Control Panel, double-click on “Network Connections” and then right-click on “Local Area Connection”, choose properties!
IMAGE1
In the window of connection to the LAN, you see the different protocols that are installed.For that you can share your files, network play, use your printers, it is important that these protocols are installed:Client for Microsoft NetworksSharing file and printer sharing for Microsoft NetworksPlanner packages QoSInternet Protocol TCP / IP
If one of these protocols you need, click “Install…” and add it.
We will now set the addresses of each computer, we should select the “Internet Protocol TCP / IP” and click “Properties”. We must now assign an IP address to each computer, it can be done automatically or you can define yourself what is by far preferable. Commonly, we will give these addresses:
PC No. 1IP address: 192.168.0.1Subnet mask: 255.255.255.0
No. 2 PCIP address: 192.168.0.2Subnet mask: 255.255.255.0
We will leave the DNS automatically. Close window with OK
Now let’s make the 2 computers belong to the same workgroup. To do this, you have to right-click the desktop and select “properties”.In the section “Computer name”, you will see the name of the computer as well as the working group in which he finds himself. Click on “network ID” to change the working group, it is preferable that computers will be 2 in the same workgroup
IMAGE2
The next step is to verify that the two PCs communicate well together. Open command prompt (MS-DOS window to win 98), opening the Start menu / run, type “cmd”):
Taper with the PC No. 1, the command “ping 192.168.0.2″ that verifies that the PC No. 1 clearly the No. 2. Then try “ping nomduPC2.”Taper with the No. 2 PC, the command “ping 192.168.0.1″ which allows to verify that the No. 2 PC clearly the No. 2. Then try “ping nomduPC1.”
The “Ipconfig / all” well lets you know the network configuration of the PC if you have done everything possible automatic.
The next step is to share files on each PC, right click on the folder you want to share, click “Sharing”, name the file as will be seen in the network.
Right-click on the icon “My Network Places” in your office then click on “Explorer” (Warning: there is a difference between Explorer and Open), click ‘entire network’ and then the working group, you see computers as well as all records and files they share. 2. With Windows 98 (Me?) Right-clicking the icon “Network Neighborhood” on your desktop and select Properties or go to the Control Panel and click on “network.”In the window “network”In the tab “Settings”, you see the different protocols that are installed as well as network cards.For that you can share your files, network play, share printers, it is important that these protocols are installed:Client for Microsoft NetworksThe name of your network cardSharing files and printers for Microsoft NetworksProtocol IPX / SPXInternet Protocol TCP / IP
If one of these protocols you need, click “Install…” and add it.
We will now set IP addresses for each computer, we should select the “Internet Protocol TCP / IP” and click on “Properties” for “open window” TCP / IP properties “We must now assign IP addresses for each computer, you can define yourself, or put them into automatic knowing that the manual method lets you control your network!Commonly, we will give these addresses:
PC No. 1IP address: 192.168.0.1Subnet mask: 255.255.255.0
No. 2 PCIP address: 192.168.0.2Subnet mask: 255.255.255.0
In general, the DNS are disabled in the event of a network between 2 computers, unless there is a shared connection to the Internet (to check if I plant it!).Now, we must make sure that all computers are in the same workgroup.In the tab “Identification” window of your “network”, you will see the name of the computer as well as the working group in which he finds himself, it is preferable that computers will be 2 in the same working group ( example: WORKGROUP)
The next step is to verify that the two PCs communicate well together.
Open a DOS window by going to “Start menu” and then “run”, type “command”:
Taper with the PC No. 1, the command “ping 192.168.0.2″ that verifies that the PC No. 1 clearly the No. 2. Then try “ping nomduPC2.”Taper with the No. 2 PC, the command “ping 192.168.0.1″ which allows to verify that the No. 2 PC clearly the No. 2. Then try “ping nomduPC1.
The “Ipconfig / all” well lets you know the configuration of the PC network at a glance.
The next step is to share files on each PC, right click on the folder you want to share in the explorer choose “share”, then take, “as sharing and name the file as it is seen in the network
Right-click on the icon “Network Neighborhood” in your office then click on “Explorer” (Warning: there is a difference between Explorer and Open), click on “Network” and then on the working group that you have created and see the computers and all the folders and files they share.II. With more computers
Each PC should be as previously fitted with a network card and the appropriate drivers installed.We will choose to connect with the cable networks right type RJ45 on a hub or a switch (the switch works as the Hub, but it is more efficient because it prevents collisions between packets and eliminates those who are affected).
The configuration must be done in the same manner as stated above, they must:Having the right protocols installed.Having the same subnet mask. (255.255.255.0)Have IP addresses of the type: - No. 1 PC - 192.168.0.1 –No. 2 PC - 192.168.0.2 –No. 3 PC - 192.168.0.3 –Etc …Being in the same workgroup. (Workgroup)III. Internet Connection Sharing.
One of the benefits of computers and the connection you want to share with others.The connection can be shared type of DSL or cable. It is assumed that this connection is already configured on the PC. One PC will act as server (PC No. 1) and other client (PC No. 2, 3 and 4 …).So we will assign the address 192.168.0.1 to the PC No. 1, which benefits from the Internet connection, other PC will respectively address IP192.168.0.2, 3 and 4 …We must now set up bridges on the PC No. 2, 3 and 4. The bridge is the IP address of No. 1 PC, which benefits from the Internet, or in our case 192.168.0.1. A. Under windows XPDans Window Properties Internet Protocol (TCP / IP) “in the” General “tab,
Enter 192.168.0.1. As a gateway for PCs No. 2, 3 and 4.Also in the “General” tab, click “Use the following DNS server address” and enter the following info:DNS Server favorite: 192.168.0.1DNS Server Auxiliary: none(They correspond to the DNS (Domain Name Server) primary and secondary).B. On a Windows PC 98Pour No. 1You must first install the service “Internet Connection Sharing.” To do this, you need to go to Start / Settings / Control Panel / Add Remove Programs / Windows Setup / Internet Tools / Select “Internet Connection Sharing”Confirm by clicking on “OK”Specify the directory of the CD Windows 98 when the system asksFor PC No. 2, 3 and 4In the window “Properties TCP / IP,” in the “Gateway” enter 192.168.0.1 as a new bridge and be sure to click add.In the section “Configuring DNS,” click “activate DNS”Then enter the following info:Host: Put the name of PC1 for all PC (except himself PC1)Area: In “DNS search order,” put “192.168.0.1″ and click add
© MetathesusIV. If a problemCheck the type of node:Start> Run then type cmdTaper: ipconfig / allFacing node type the word or Unknown Hybrid. Otherwise:Click on Start> Run then type: regeditBrowse: HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Services \ NetBT \ Parameters.Deleting an entry bearing one of these two names: NodeType or DhcpNodeType.Finish restarting the computer.Make sure NetBIOS is enabled:With the right mouse button, click on the network connection and then click Properties.Select the TCP / IP protocol and then on Properties.Click on Advanced, then WINS tab.Select “Enable NetBIOS with TCP / IP”.Make sure NetBIOS is enabled by using the command:Start> execute> cmd.exe> ipconfig / all
Make sure the firewall is not blocking computers on the LANIf necessary, disable it a short time to target the problem. See:5BS%% E9curit% E9% 5D% d Use firewall 27un
More network problems:Http://www.hotline-pc.org/reseauproblemes.htm
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List of open ports
Posted on April 23, 2008 by salahsamy
Que vous soyez sous Windows ou Linux/Unix, la commande suivante (en console) permet d’afficher la liste des ports ouverts sur votre ordinateur :netstat -a