Arista Networks Arista Networks Arista Networks VMware VMware Tools like traceroute have been very valuable for the operation of the Internet. Part of that value comes from being able to display information about routers and paths over which the user of the tool has no control, but the traceroute output can be passed along to someone else that can further investigate or fix the problem. In overlay networks such as VXLAN and NVGRE the prevailing view is that since the overlay network has no control of the underlay there needs to be special tools and agreements to enable extracting traces from the underlay. We argue that enabling visibility into the underlay and using existing tools like traceroute has been overlooked and would add value in many deployments of overlay networks. This document specifies an approach that can be used to make traceroute transcend layers of encapsulation including details for how to apply this to VXLAN. The technique can be applied to other encapsulations used for overlay networks. It can also be implemented using current commercial silicon.