When you never hear from the other side for long enough you can reasonably assume that the communication channel is no longer open. Instead you can measure time since last message from your peers. Whenever you are trying to know when the other end of the communication still participate in it or not, you cannot expect the other side to tell you about it, because if theirs only way of communication with you is gone they have no means to do so. Listening – listens what Active and Standby routers are doing and waits to be promoted to Standby or Active role.Standby – the first one in the queue, should the Active router go off line.Router in a first-hop redundancy setup can be in on of the following states: States of routers for different protocols All the other routers will ‘pretend’ not to be there and wait for their turn, either when the active router, go off-line or it will be the turn of a given router in a round-robin load-balancing.
Each one of them knows IP and MAC address of the group, but only one of them will respond to an attempt of communication from the client. The routers in the group decide between themselves which one should respond.
When a client is trying to contact the Internet, it is configured to go via virtual IP address. The routers perform the magic between themselves. This way the client/desktop computer doesn’t need to even ‘know’ that it is connected to a group of routers. The routers which should provide redundancy or load balancing are configured as a group and have common virtual IP and virtual MAC addresses.
To help the situation for purposes of first hop redundancy or gateway load balancing the virtual IP and MAC addresses are used.
For the Cisco certification the candidates are required to have some basic understanding of the Gateway Redundancy Protocols: FHRP, HSRP, VRRP, GLBP. The first hop redundancy, gateway load balancing is really not that scary or difficult.