Cloudflare, Inc.
METHOD AND SYSTEM FOR DETERMINING A PATH MAXIMUM TRANSMISSION UNIT (MTU) BETWEEN ENDPOINTS OF A GENERIC ROUTING ENCAPSULATION (GRE) TUNNEL

Abstract:

A method of path MTU determination in Generic Routing Encapsulation (GRE) tunnel is presented. A source network device (ND) transmits, to a destination ND that is a second endpoint of the GRE tunnel, a first outer packet including a first inner packet, where the first inner packet includes a first inner header that is used to deliver the first inner packet to the source network device, a first inner GRE header, and a first payload. The source ND receives the first inner packet. The source ND transmits a second outer packet including a second inner packet that includes a second payload that has a size greater than a size of the first payload. The source ND determines that the second inner packet is not received and determines a path MTU between the source ND and the destination ND based on a size of the first and the second outer packets.