So first off, do ethernet sends ack frames or not?
if it doesn't : then how does a router know whether its neighbors are down or not?
if it does : then is it cumulative ack with an ack timer or one ack per received frame?
I'm asking this because in Link state algorithm i read somewhere that the blackhole problem is solved by the router because it will eventually realize that its neighbor is down, but how can it know if there is no ack frames?
Best Answer
No, ethernet is connectionless, as is IP, and if you use UDP, the application would need to perform any connection-related handshaking (if needed). Typically, it is the responsibility of the transport or application protocol, e.g. TCP, to establish connections.
Sometimes (statically configured routes), a router has no idea if a neighbor is down. If the routers share a routing protocol, it is up to the routing protocol (at the transport or application layer) to determine that a neighbor is down.
No, ethernet has no idea if frames are dropped or lost. There is no ACK because there is no connection established. Ethernet will silently drop damaged or excess frames. It is the job of upper-layer protocols or applications to notice that data are missing.