I wonder keepalive format.
also how the device(switch or router) checks the keepalive about attated host.
I know "TCP keepalive" and "keepalive"(used in switch/router)
(I know TCP keepalive well)
could anyone explain me about keepalive check method and format??
I've found a better explanation:
an ethernet keepalive is an ethernet frame with
MAC SA = MAC DA = router interface MAC address
and with ethertype 0x9000
this special ethertype calls for loopback: the device that receives the frame sends it back.
So by receiving its own frames with SA= DA = router interface MAC a router can put its interface as up/up.
Actually a trick I used some years ago to have ethernet ports to stay up/up even if unplugged was to disable keepalive (it was for lab tests).
Hope to help