Netgear produces networking equipment for home and office environments. The manufacturer's product range includes cabled, wireless and powerline network media. The Maximum Transmission Unit, or MTU, is the largest block of data that a network can handle.
Data Packets
Data and messages travel across networks and over the Internet in segments. These segments are organized into a structure called a packet. A network transport protocol (there are two alternative systems) dictates how the the data is placed into a packet. The transport protocol puts a header on the front of the data packet. This contains source and destination application details under one scheme (User Datagram Protocol), and additional connection details under the other (Transmission Control Protocol). The number of headers on the front of a data packet depends on the application sending the data. However, there is always a transport protocol header and there is always an IP header. The IP header is always the front-most header on the packet. It is organized by the Internet Protocol and contains the source and destination IP addresses for the packet. The IP header also contains fields for fragmentation. Fragmentation is an action closely related to the MTU of a network.
Fragmentation
The MTU dictates the longest data packet the network will handle. This number of bytes includes all the headers on the packet. Data travelling over the Internet crosses several private networks. Any one of those networks may have an MTU lower than the size of the packet. When this happens, the receiving router will beak up the packet into smaller units. This is fragmentation. This increases overhead on the packets. Overhead is the proportion of header bytes to data bytes. Overhead is lower on larger packets. The IP header contains a flag that forbids fragmentation. If this is set, the router of the network with a lower MTU will drop the packet and notify the sender. This causes transmission delays or lost connections if the sending program decides not to retry the transmission.
Recommendations
Fragmentation isn't a desirable process and should be avoided. Netgear does not produce any recommendations for MTU on its equipment, but recommends the standard defaults set by Microsoft in its Windows networking software. Windows follows the Ethernet standard of 1,500 bytes for a network MTU, or 1,400 bytes for a Virtual Private Networks (which add on extra headers).
Internet Service Providers
Ethernet is the most widely implemented standard for the physical properties of networks. Thus, its recommendations on Maximum Transmission Unit settings is a worthwhile standard to follow. However, some network users with this setting may experience problems when connecting to the Internet. This is because some Internet service providers use a system called Point-to-Point over Ethernet (PPPoE) to manage connections to clients. This protocol adds an extra field to the packet header, leaving less space for the regular IP packet. In these instances, an MTU of 1,492 bytes is recommended.
