Path maximum transmission unit discovery

• US 10,462,065 B2
• Filed: 08/13/2014
• Issued: 10/29/2019
• Est. Priority Date: 06/29/2014
• Status: Active Grant

• Current Assignee: Vmware LLC (Broadcom, Inc.)
• Original Assignee: VMware, Inc. (Broadcom, Inc.)
• Inventors: Sreeramoju, Akshay Kumar
• Primary Examiner(s): Mesfin, Yemane
• Assistant Examiner(s): Banthrongsack, Jeff
• Application Number:
  US14/458,257
• Publication Number:
  US 20150381509A1
• Time in Patent Office: 1,903 Days
• Field of Search: None
• CPC Class Codes: H04L 47/365 Dynamic adaptation of the packet size
• CPC Class Codes: H04L 69/166 IP fragmentation; TCP segmentation

Abstract

An example method is provided for a source device to perform discovery of a path maximum transmission unit (PMTU) of a path between the source device and a destination device in a communications network. The method may comprise configuring and sending a request message to the destination device via an intermediate device on the path. The request message may be configured to have a size of an estimated PMTU of the path, to cause a reply message to be received from the destination device or at least one report message to be received from the intermediate device, and to include a flag that allows fragmentation of the request message. The method may further comprise receiving the reply message from the destination device or the at least one report message from the intermediate device responsive to the request message; and based on the reply message or the at least one report message, determining that fragmentation of the request message has occurred because the estimated PMTU is greater than an actual PMTU and updating the estimated PMTU.

Claims

1. A method for a source device to perform discovery of a path maximum transmission unit (PMTU) of a path between the source device and a destination device in a communications network, comprising:

configuring, by the source device, a request message to have a size of an estimated PMTU of the path, wherein the estimated PMTU of the path is greater than an actual PMTU of the path, to cause multiple fragments of a reply message to be received from the destination device or multiple report messages to be received from an intermediate device on the path, and to include a flag that allows fragmentation of the request message into multiple fragments;

sending, by the source device, the request message to the destination device via the intermediate device;

receiving, by the source device, the multiple fragments of the reply message from the destination device, or the multiple report messages from the intermediate device responsive to the multiple fragments of the request message; and

based on the multiple fragments of the reply message or the multiple report messages,

determining, by the source device, that fragmentation of the request message has occurred because the estimated PMTU is greater than the actual PMTU; and

updating, by the source device, the estimated PMTU based on a largest fragment among the multiple fragments of the reply message or among the multiple fragments of the request message.

2. The method of claim 1, wherein determining that fragmentation of the request message has occurred comprises:

determining that the multiple report messages from the intermediate device each include a length of one of the multiple fragments of the request message.

3. The method of claim 2, wherein updating the estimated PMTU based on the at least one report message comprises:

based on the length included in each of the multiple report messages, determining the largest fragment among the multiple fragments of the request message.

4. The method of claim 1, wherein configuring the request message further comprises:

configuring the request message to have a time to live (TTL) parameter that expires at the intermediate device, wherein expiry of the TTL parameter causes the intermediate device to send the multiple report messages in the form of TTL expired messages.

5. The method of claim 4, further comprising:

sending a further request message addressed to the destination device via the intermediate device and a further intermediate device on the path,

wherein the further request message is configured to have a size of the updated estimated PMTU, to cause a further report message from the further intermediate device by updating the TTL parameter and to have a flag that allows fragmentation of the further request message;

receiving the further report message from the further intermediate device responsive to the further request message; and

in response to determining that fragmentation of the further request message has occurred, further updating the updated estimated PMTU based on the further report message.

6. The method of claim 5, further comprising repeatedly sending the further request message and updating the estimated PMTU until the reply message is received from the destination device.

7. The method of claim 1, wherein determining that fragmentation of the request message has occurred comprises:

based on the multiple fragments of the reply message, determining that fragmentation of the reply message from the destination device has occurred, wherein the reply message sent by the destination device is substantially the same size as the request message sent by the source device.

8. The method of claim 1, wherein configuring the request message comprises:

configuring the request message to have a TTL parameter that does not expire at the intermediate device, wherein the non-expiry of the TTL parameter allows the request message to reach the destination device to cause the destination device to send the reply message to the source device.

9. The method of claim 1, wherein updating the estimated PMTU based on the reply message comprises:

determining the largest fragment among the multiple fragments of the reply message based on an initial fragment of the reply message.

10. The method of claim 1, wherein:

the request message is an echo request message; and

the reply message is an echo reply message that is configured to have the size of the estimated PMTU of the path and the flag that allows fragmentation of the echo reply message before reaching the source device.

11. The method of claim 1, wherein the request message is configured to cause the:

the reply message from the destination device if routing between the source device and the destination device is symmetric;

or

the at least one report message from the intermediate device if routing between the source device and the destination device is asymmetric.

12. A non-transitory computer-readable storage medium that includes a set of instructions which, in response to execution by a processor, causes the processor to perform a method for a source device to perform discovery of a path maximum transmission unit (PMTU) of a path between the source device and a destination device in a communications network, the method comprising:

configuring, by the source device, a request message to have a size of an estimated PMTU of the path, wherein the estimated PMTU of the path is greater than an actual PMTU of the path, to cause multiple fragments of a reply message to be received from the destination device or multiple report messages to be received from an intermediate device on the path, and to include a flag that allows fragmentation of the request message into multiple fragments;

sending, by the source device, the request message to the destination device via the intermediate device;

receiving, by the source device, the multiple fragments of the reply message from the destination device, or the multiple report messages from the intermediate device responsive to the multiple fragments of the request message; and

based on the multiple fragments of the reply message or the multiple report messages,

determining, by the source device, that fragmentation of the request message has occurred because the estimated PMTU is greater than the actual PMTU; and

updating, by the source device, the estimated PMTU based on a largest fragment among the multiple fragments of the reply message or among the multiple fragments of the request message.

13. The non-transitory computer-readable storage medium of claim 12, determining that fragmentation of the request message has occurred comprises:

determining that the multiple report messages from the intermediate device each include a length of one of the multiple fragments of the request message.

14. The non-transitory computer-readable storage medium of claim 13, wherein updating the estimated PMTU based on the at least one report message comprises:

based on the length included in each of the multiple report messages, determining the largest fragment among the multiple fragments of the request message.

15. The non-transitory computer-readable storage medium of claim 12, wherein configuring the request message comprises:

configuring the request message to have a time to live (TTL) parameter that expires at the intermediate device, wherein expiry of the TTL parameter causes the intermediate device to send the multiple report messages in the form of TTL expired messages.

16. The non-transitory computer-readable storage medium of claim 14, further comprising:

sending a further request message addressed to the destination device via the intermediate device and a further intermediate device on the path,

wherein the further request message is configured to have a size of the updated estimated PMTU, to cause a further report message from the further intermediate device by updating the TTL parameter and to have a flag that allows fragmentation of the further request message;

receiving the further report message from the further intermediate device responsive to the further request message; and

in response to determining that fragmentation of the further request message has occurred, further updating the updated estimated PMTU based on the further report message.

17. The non-transitory computer-readable storage medium of claim 16, further comprising repeatedly sending the further request message and updating the estimated PMTU until the reply message is received from the destination device.

18. The non-transitory computer-readable storage medium of claim 12, wherein determining that fragmentation of the request message has occurred comprises:

based on the multiple fragments of the reply message, determining that fragmentation of the reply message from the destination device has occurred, wherein the reply message sent by the destination device is substantially the same size as the request message sent by the source device.

19. The non-transitory computer-readable storage medium of claim 12, wherein configuring the request message comprises:

configuring the request message to have a TTL parameter that does not expire at the intermediate device, wherein non-expiry of the TTL parameter allows the request message to reach the destination device and to cause the destination device to send the reply message to the source device.

20. The non-transitory computer-readable storage medium of claim 12, wherein updating the estimated PMTU based on the reply message comprises:

determining the largest fragment among the multiple fragments of the reply message based on an initial fragment of the reply message.

21. The non-transitory computer-readable storage medium of claim 12, wherein:

the request message is an echo request message; and

the reply message is an echo reply message that is configured to have the size of the estimated PMTU of the path and the flag that allows fragmentation of the echo reply message before reaching the source device.

22. The non-transitory computer-readable storage medium of claim 12, wherein the request message is configured to cause:

the reply message from the destination device if routing between the source device and the destination device is symmetric;

or

the at least one report message from the intermediate device if routing between the source device and the destination device is asymmetric.