Loopback interfaces:
127 are full network as a loopback address.
Pass a broadcast address or multicast IP packets a copy to the loopback interface, and then transferred to the Ethernet. This is because the definition of broadcast transmission and multicast transmission contain themselves.
Any data transmitted to the host IP address are sent to the loopback interface.
LAN communication is not logical hardware address by address. To see whether the machine has the logical address of the ARP mapping hardware address of the machine, and if not will automatically send ARP packet parsing, etc. The reward would return back updates the ARP table, only a transmission packet destined object ground.
Path MTU and MTU
802.3 pairs of Ethernet data frame length and has a limit which is the maximum value of 1500 and 1492 bytes, respectively (since 8023 adds 8 bytes). This feature is referred to as the link layer MTU, Maximum Transmission Unit.
If the IP layer to transmit a data packet, and the length of the data link layer is larger than the MTU, then the IP layer needs to be fragmented (fragmentation), the data packet into pieces, so that each one is less than MTU.
MTU point link layer (e.g., SLIP and PPP) does not refer to a physical characteristic of the network medium. Instead, he is a logical limitation, an object to provide sufficiently fast response time to interactive use.
Two communicating hosts minimum path MTU, which is called the path MTU.
Path MTU in two directions is not necessarily the same.
MTU is calculated direction.
