Adaptive private network with path maximum transmission unit (MTU) discovery process

摘要

Systems and techniques are described for a path maximum transmission unit (MTU) discovery method that allows the sender of IP packets to discover the MTU of packets that it is sending over a conduit to a given destination. The MTU is the largest packet that can be sent through the network along a path without requiring fragmentation. The path MTU discovery method actively probes each sending path of each conduit with fragmentation enabled to determine a current MTU and accordingly increase or decrease the conduit MTU. The path MTU discovery process is resilient to errors and supports retransmission if packets are lost in the discovery process. The path MTU discovery process is dynamically adjusted at a periodic rate to adjust to varying network conditions.

主权项

1. A method in a network node to dynamically adjust a maximum transmission unit (MTU) using an MTU search probe, the method comprising:
transmitting from node A to node B a path MTU probe request packet that requests a reply message be returned when fragmentation does not occur and when fragmentation does occur, that is configured with path MTU probe information having a selected MTU size value subsequently followed with padding and without user data, the path MTU probe request packet having a packet length according to the selected MTU size value, and the path MTU probe request packet configured to be fragmented if the packet is too large without fragmenting user data; transmitting from node A to node B a path MTU probe trailer request packet that requests a reply message be returned and having a packet length significantly smaller than the selected MTU size value to allow the path MTU probe trailer request packet to be received at node B even if the path MTU probe request packet was dropped before reaching node B, wherein the MTU search probe begins with the transmission of the path MTU probe request packet followed in sequence by the transmission of the path MTU probe trailer request packet; determining a path MTU received probe reply packet having an Internet protocol (IP) datagram length that is then received at node A in response to the path MTU probe request packet that was received at node B without fragmentation and the path MTU probe trailer request packet received at node B is ignored at node B in response to the path MTU probe request packet that was received at node B; and increasing the selected MTU size value at node A upon determining the IP datagram length of the received path MTU received probe reply packet is the same as the selected MTU size value defined in the path MTU probe request packet, wherein a subsequent MTU search probe utilizes the increased MTU size value to search for an MTU value that is larger than the selected MTU size value.