Browse Prior Art Database

Method for Path MTU Discovery in Overlay Environments

IP.com Disclosure Number: IPCOM000223770D
Publication Date: 2012-Nov-28
Document File: 4 page(s) / 30K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to use Path Maximum Transmission Unit (MTU) Discovery on VXLAN Tunnel End Point (VTEP) in overlay environments.

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Method for Path MTU Discovery in Overlay Environments

It is a trend today to use overlay to separate the server world from the Data Center (DC) networking world. The use of overlay, however, increases the frame size on the wire and, thus, causes a frame be dropped on the network. An Internet Control Message Protocol (ICMP) Packet Too Big (PTB) message may be sent back to the sender by the switch that drops the frame, if it is an IP packet. The message may either not be sent by the switch, or be dropped on its way to the sender due to many reasons: firewall, congestion, etc. In addition, the destination of an ICMP PTB message in the overlay environment is the sending VXLAN Tunnel End Point (VTEP), not the Virtual Machine (VM) that sends the original frame. This causes the black hole issue on the protocol stack of a VM, since it receives no indication back about why its frames are dropped on the wire. It is very important for a VM to discover the Path Maximum Transmission Unit (PMTU) in an overlay environment as soon as possible in order to react much quicker, or at least the VTEP should have enough information to help trouble-shoot a network problem.

The use of Path MTU Discovery (PMTUD) is important in an overlay environment. This is especially true on the VTEP since it is the endpoint of a tunnel - the ICMP PTB messages will be passed only to the VTEP, not to the VMs on its top. The application stack in VM usually receives no ICMP PTB messages back at all in overlay environments.

This invention proposes the use of Path MTU Discovery on VTEP in overlay environments. The method is similar to that PMTU Discovery used in a Transmission Control Protocol (TCP) environment, but with some modifications. This invention provides the following benefits,


• The VM on the top of a VTEP can receive ICMP PTB (Packet Too Big) messages when its frame size exceeds the PMTU allowed on the path, if the frame sent out is an IP packet. With this, the black hole problem in the protocol stack of a VM can be avoided.


• If the application running in VM is using L2 frames, the counters supported on VTEP can help trouble shoot the problem


• The two VTEPs for a tunnel in overlay environments can exchange information with each other via the probing process for PMTUD. With this, a VTEP can know if its peer VTEP for a tunnel is capable of IP packet reassembly or not.


• The sending VTEP can perform frame fragmentation if the destination VTEP supports IP packet reassembly, even if the carried frame is a L2 packet

The use of Path MTU (PMTU) discovery is common in TCP. Here, a similar method is used on the VTEP with some modifications; the modifications are necessary in order for the VMs on its top to work better.

The novel contributions of the invention include:


• The use of PMTUD on VTEP in overlay environments


• Mechanism for information exchange via the probe packets of PMTUD in

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between the two VTEPs


• The use of packet fragmentatio...