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The process is repeated until the MTU is small enough to traverse the entire path without fragmentation. As IPv6 routers do not fragment packets, there is no Don't Fragment option in the IPv6 header. For IPv6, Path MTU Discovery works by initially assuming the path MTU is the same as the MTU on the link layer interface where the traffic originates.
The MTU is specified in terms of bytes or octets of the largest PDU that the layer can pass onwards. MTU parameters usually appear in association with a communications interface (NIC, serial port, etc.). Standards (Ethernet, for example) can fix the size of an MTU; or systems (such as point-to-point serial links) may decide MTU at connect time.
The TCP should ask the IP for the Maximum Datagram Data Size (MDDS). This is the MTU minus the IP header length (MDDS = MTU − IPHdrLen). When opening a connection, TCP can send an MSS option with the value equal to: MDDS − TCPHdrLen. In other words, the MSS value to send is: MSS = MTU − TCPHdrLen − IPHdrLen
The option value is derived from the maximum transmission unit (MTU) size of the data link layer of the networks to which the sender and receiver are directly attached. TCP senders can use path MTU discovery to infer the minimum MTU along the network path between the sender and receiver, and use this to dynamically adjust the MSS to avoid IP ...
In contrast to IPv4, routers do not fragment IPv6 packets larger than the maximum transmission unit (MTU), it is the sole responsibility of the originating node. A minimum MTU of 1,280 octets is mandated by IPv6, but hosts are "strongly recommended" to use Path MTU Discovery to take advantage of MTUs greater than the minimum.
The frame size used by an end-to-end connection is typically limited by the lowest frame size in intermediate links. 802.5 Token Ring can support frames with a 4464-byte MTU, FDDI can transport 4352-byte, ATM 9180-byte and 802.11 can transport 7935-byte MTUs.
Linux also features iwspy, to read the signal, noise and quality of a wireless connection. Other related tools for configuring Ethernet adapters are: ethtool, mii-tool, and mii-diag in Linux and the command dladm show-link in Solaris. The ip suite has a similar purpose and is meant to replace the deprecated ifconfig. [6]
On Linux and all Unix-like operating systems, the utilities ifconfig and the newer ip (from the iproute2-bundle) are used to configure IEEE 802.3 and IEEE 802.11 hardware. These utilities configure the kernel directly and the configuration is applied immediately. After boot-up, the user is required to configure them again.