Second, the TTL field has the meaning of a threshold value. We have to avoid multicast packets from being routed out of the local area network or routing range. Otherwise, parts of the Internet could be loaded with undesired multicast packets. This is why we split the potential reach of a multicast packet into different zones. These zones are controlled by the TTL value specified in the packets. If a multicast packet exceeds a zone, it has to have a sufficient residual lifetime to overcome this hurdle.