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Maximum Path MTU Detection for Multipath Routes

IP.com Disclosure Number: IPCOM000012063D
Original Publication Date: 2003-Apr-04
Included in the Prior Art Database: 2003-Apr-04
Document File: 1 page(s) / 50K

Publishing Venue

IBM

Abstract

Routing tables in today's operating systems often have several matches in the routing table for a single destination address. The current routing mechanisms typically pick one route with the best key match and the best cost and this route is then exclusively used for this communication session. The problem with this approach is with applications that have large data to send. These applications are more concerned with the Path MTU (Maximum Transmission Unit) for the route. The current approach picks the best route based only on a key match and a cost which often does not factor in the path MTU at all. This idea suggests a routing mechanism for picking a route that focuses on finding the largest path MTU.

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Maximum Path MTU Detection for Multipath Routes

The new routing mechanism would walk through the routing table and for each and every possible route 'r' to the given destination, conduct the following process: - Carry out a Path MTU Discovery mechanism for route 'r'. This mechanism is already available in most operating systems. - Check if the Path MTU for 'r' is bigger than the current biggest path MTU stored in mtu.

    If it is bigger, then save a pointer to this route in a pointer rbig and save the path MTU in mtu

If it is not, then the current values for rbig and mtu are unchanged

When all the route matches in the routing table are complete, rbigwill contain the route that has the biggest PMTU value mtu.

Note that all applications may not want to find the largest path MTU for their communication session. Some applications will be willing to accept any route that is selected by the current routing mechanism. Thus we will define a new socket option SO_FIND_BIGGEST_MTU. This socket option must be set by applications that want the enhanced routing mechanism to be used for their route selections.

Disclosed by International Business Machines Corporation

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