Maximum transmission unit installation for network traffic along a datapath in a software defined network

1. A method comprising:

determining, from a maximum transmission unit (MTU) database and with a software-defined network (SDN) controller in an SDN, MTU sizes for switches along a datapath in the SDN, wherein the SDN controller controls a plurality of the switches along the datapath in accordance with a SDN protocol;

selecting one of the determined MTU sizes as the largest allowable MTU size for the datapath; and

installing, on a controlled switch along the datapath, the largest allowable MTU size as the MTU size for traffic along the datapath, which includes:

installing, on a controlled switch along a first datapath, a first datapath's largest allowable MTU size as the MTU size for traffic along the first datapath; and

installing, on a controlled switch along a second datapath, a second datapath's largest allowable MTU size as the MTU size for traffic along the second datapath.

2. The method of claim 1 , wherein the largest allowable MTU size is installed on a first controlled switch along the datapath.

3. The method of claim 1 , wherein the largest allowable MTU size is installed on a controlled switch selected to minimize the number of times a packet is to be fragmented along the datapath.

4. The method of claim 1 , wherein the smallest MTU size among the determined MTU sizes is selected as the largest allowable MTU size for traffic along the datapath.

5. The method of claim 1 , wherein the controlled node switch along the first datapath is the same node switch as the controlled node switch along the second datapath.

6. The method of claim 1 , further comprising:

receiving an MTU value for a controlled switch that has been added to the SDN; and

storing, in the MTU database, the received MTU value for the added controlled switch.

7. The method of claim 1 , further comprising:

querying each controlled switch in the SDN for its respective MTU value; and

storing, in the MTU database, received MTU values for each queried switch.

8. The method of claim 1 , further comprising:

receiving an indication that a controlled switch has been removed from the SDN; and

removing, from the MTU database, the MTU value for the removed switch.

9. The method of claim 1 , further comprising:

receiving a packet from the controlled switch along the datapath, the packet indicating a destination node for the packet; and

determining the datapath based on the destination node.

10. The method of claim 1 , wherein at least one switch along the datapath is controlled by the SDN controller, and

wherein at least one switch along the datapath is not controlled by the SDN controller.

11. A software-defined network (SDN) controller comprising:

an access module to access a maximum transmission unit (MTU) database that includes stored MTU values for switches along a datapath between a source node and a destination node in an SDN;

a MTU size determination module to determine, based on accessed values from the MTU database, a largest allowable MTU size for the datapath; and

a communication module to provide the largest allowable MTU size to a controlled switch along the datapath with instructions for the controlled switch to install the largest allowable MTU size as an MTU for traffic along the datapath,

wherein the SDN controller controls a plurality of the switches along the datapath in accordance with a SDN protocol; and

wherein installing the largest allowable MTU size includes:

installing, on a controlled switch along a first datapath, a first datapath's largest allowable MTU size as the MTU size for traffic along the first datapath; and

installing, on a controlled switch along a second datapath, a second datapath's largest allowable MTU size as the MTU size for traffic along the second datapath.

12. The SDN controller of claim 11 , wherein the communication module includes a physical data port connected to another node in the SDN via a wired link to send and receive data over the link.

13. The SDN controller of claim 11 , further comprising:

a datapath determination module to determine the datapath for traffic based on the type of traffic, network conditions, the source node and the destination node.

14. A non-transitory machine-readable storage medium encoded with instructions executable by a processor of a software-defined network (SDN) controller, the instructions comprising:

instructions to determine, based on maximum transmission unit (MTU) size values stored in an MTU database, MTU size values for switches along a datapath in the SDN, wherein the SDN controller controls a plurality of the switches along the datapath in accordance with a SDN protocol;

instructions to store the smallest MTU size among the determined MTU sizes as the largest allowable MTU size for the datapath; and

instructions to install, on a switch controlled by the SDN controller along the datapath, the largest allowable MTU size as the MTU size for traffic along the datapath, which includes:

installing, on a controlled switch along a first datapath, a first datapath's largest allowable MTU size as the MTU size for traffic along the first datapath; and

installing, on a controlled switch along a second datapath, a second datapath's largest allowable MTU size as the MTU size for traffic along the second datapath.