Method of determining path maximum transmission unit

• US 20050005024A1
• Filed: 10/29/2003
• Published: 01/06/2005
• Est. Priority Date: 10/30/2002
• Status: Active Grant

• Current Assignee: Citrix Systems, Inc. (Cloud Software Group)
• Original Assignee: Orbital Data Corporation (Cloud Software Group)
• Inventors: Samuels, Allen, Sutter, Paul
• Granted Patent: US 7,542,471 B2
• Time in Patent Office: Days
• US Class Current: 709/238
• CPC Class Codes: H04L 67/2876 Pairs of inter-processing entities at each side of the network, e.g. split proxies
• CPC Class Codes: H04L 67/56 Provisioning of proxy services store-and-forward switching systems in data switching networks H04L12/54
• 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

Abstract

Network endpoints using TCP/IP operate to determine the maximum transmission unit (MTU) of the path between them. This determination is done so as to avoid the expensive IP fragmentation that will occur when transitting links with a smaller MTU size. The standard method of determining the path MTU (PMTU) has several known deficiencies, including: inefficient use of bandwidth as proper operation will likely result in the loss of one or more packets and difficulty of implementation as the reverse channel communication mechanism, reception of ICMP messages indicating the discarding of unfragmentable packets, is frequently blocked by firewalls and other security apparatus. A method of determining the PMTU between intermediate proxies is disclosed that does not require reception of ICMP messages or the inefficient use of bandwidth due to the presumed dropping of packets with valid data.

Claims

1. A method of performing path maximum transmission unit (PMTU) discovery when two proxies are modifying a connection between a client and a server comprising the steps of:

receiving one or more packets from a client by a first proxy;

estimating a new PMTU, larger than the current PMTU;

repacketizing said client packets into at least one new packet according to the new PMTU;

transmitting said at least one new packet;

receiving said at least one new packet by a second proxy;

detecting fragmentation or non-fragmentation of said at least one new packet;

generating notification of the results of said fragmentation detecting step; and

transmitted said notification to said first proxy.