Is there an ethernet ping tool? What I'm thinking about is a tool that opens a raw socket (requires root access, of course), bound to a specified interface (option to send over all ethernet interfaces at once would be nice), and send an ethernet frame to a specified MAC address. The frame needs to be something that would evoke some kind of response if the ethernet path to there and back is working. I just don't know if ethernet itself has anything that would do this outside of the scope of ARP, IP, or IP6.

One thing that would be important is to NOT give a false response on another interface. If a machine two interfaces on a given ethernet LAN such that a frame destined for eth0 can be seen by eth1, and if eth0 is non-functional, then seeing that frame over eth1 (as long as eth1 is not configured to fake the MAC of eth0) must not result in a response.

I'm currently doing pings to IPv6 link addresses. That gives me what I want in some cases, but is a bit inconvenient. In other cases it doesn't work at all because the machines don't have IPv6 implemented, deployed, or enabled.

You can, or you used to be able to, ping a MAC address to/from Cisco routers, but generally speaking I don't think most kit supports this.

I found this: http://wiki.wireshark.org/Loop

It appears that wireshark will not actually trigger this, but will capture any activity. So there appears to be a mechanism available to do this with ethertype 0x9000 named "Configuration Test Protocol (Loop)".

See also: http://en.wikipedia.org/wiki/EtherType