System and method for discovering path MTU of internet paths

• US 5,959,974 A
• Filed: 12/02/1996
• Issued: 09/28/1999
• Est. Priority Date: 12/02/1996
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Russell, Lance Warren, Marquardt, David Richard, Wise, Larry Steven, Rao, Satyanarayana Billekal, Badt, Daniel Edward
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Nguyen, Kim T.
• Application Number:
  US08/755,864
• Time in Patent Office: 1,030 Days
• Field of Search: 370/248, 370/249, 370/400, 370/401, 370/402, 370/389, 370/392, 370/465, 370/474, 370/233, 370/252, 370/253
• US Class Current: 370/233
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/36 by determining packet size, e.g. maximum transfer unit [MTU]
• CPC Class Codes: H04L 69/16 Implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP]
• CPC Class Codes: H04L 69/166 IP fragmentation; TCP segmentation
• CPC Class Codes: H04L 69/24 Negotiation of communication capabilities
• CPC Class Codes: H04L 69/325 in the network layer [OSI layer 3], e.g. X.25 H04L69/16 takes precedence
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04M 7/006 Networks other than PSTN/ISDN providing telephone service, e.g. Voice over Internet Protocol (VoIP) , including next generation networks with a packet-switched transport layer H04L65/00 takes precedence; aspects not specific to the type of network H04M3/00; special services in those networks H04M3/42

Abstract

A local system issues an ICMP echo request packet with a size based on an initial PMTU value corresponding to that of the local system'"'"'s interface MTU. When an ICMP needfrag error packet is received by the local system, this signifies that the initial PMTU value was too large for packets of corresponding size to be transmitted through the Internet without fragmentation. The value is accordingly decreased by the local system and a next ICMP echo request packet transmitted through the Internet. The process iterates until an ICMP echo request packet is successfully transmitted through the Internet to a target system. In response thereto, the target system transmits an ICMP echo response packet back through the Internet to the local system, thereby indicating that the last-sent ICMP echo request packet from the local system had the correct PMTU value which is thereafter assumed to be the correct PMTU.

Claims

1. A method for discovering path maximum transfer unit (PMTU) in an Internet system having a local system and a target system interconnected by said Internet, comprising:

transmitting an Internet control message protocol (ICMP) echo request packet independent of payload data with the DF bit set from said local system onto said Internet;

receiving from said target system at said local system an ICMP echo response packet;

detecting at said local system an ICMP needfrag error packet;

reducing said initial PMTU value by an amount determined from said local system; and

resending from said local system a next PMTU value containing said reduced PMTU value.

2. The method of claim 1, further including the steps of:

receiving at said local system a next ICMP needfrag error packet in response to said sending a next ICMP echo request packet;

reducing said reduced PMTU value in response to said receiving said next ICMP needfrag error packet;

sending from said local system a next ICMP echo request packet containing said next reduced PMTU value; and

repeating the above steps until said ICMP echo response packet is received.

3. The method of claim 2 wherein said initial PMTU value is the value of the MTU of the interface between said local system and said Internet.

4. An apparatus for discovering path maximum transfer unit (PMTU) in an Internet system having a local system and a target system interconnected by said Internet, comprising:

means for transmitting an Internet control message protocol (ICMP) echo request packet independent of payload data with the DF bit set from said local system onto said Internet;

means for receiving from said target system at said local system an ICMP echo response packet;

means for detecting at said local system an ICMP needfrag error packet;

means for reducing said initial PMTU value by an amount determined from said local system; and

means for resending from said local system a next PMTU value containing said reduced PMTU value.

5. The apparatus of claim 4 further including:

means for receiving at said local system a next ICMP needfrag error packet in response to said sending a next ICMP echo request packet;

means for reducing said reduced PMTU value in response to said receiving said next ICMP needfrag error packet;

means for sending from said local system a next ICMP echo request packet containing said next reduced PMTU value; and

means for repeating the above steps until said ICMP echo response packet is received.

6. The apparatus of claim 5 wherein said initial PMTU value is the value of the MTU of the interface between said local system and said Internet.