Hop Count

In computer networking, hop count refers to the intermediate devices (like routers) through which data must pass between source and destination, rather than flowing directly over a single wire. Each router along the data path constitutes a hop, as the data is moved from one Layer 3 network to another. Hop count is therefore a basic measurement of distance in an network.

By itself, hop count is not a useful metric for determining the optimum network path, as it does not take into consideration the speed, load, reliability, or latency of any particular hop, but merely the total count. Nevertheless, some routing protocols such as RIP use hop count as their sole metric.

Hop counts are often useful to find faults in a network, or to discover if routing is indeed correct. Network utilities like Ping can be used to determine the hop count to a specific destination. Ping generates packets that include a field reserved for the hop count. Each time a capable device receives these packets, that device modifies the packet, incrementing the hop count by one. In addition, the device compares the hop count against a predetermined limit and discards the packet if its hop count is too high. This prevents packets from endlessly bouncing around the network due to routing errors. Both routers and bridges are capable of managing hop counts, but other types of intermediate devices (like hubs) are not.

Other articles related to "hop, hop count, hop counts, hops":

Amorphous Computing - Algorithms, Tools, and Patterns
... (Ref 1) A device emits a message with an encoded hop-count ... Devices which have not seen the message previously, increment the hop count, and re-broadcast ... A wave propagates through the medium and the hop-count across the medium will effectively encode a distance gradient from the source ...
Route Poisoning
... with poison reverse, route poisoning provides for sending updates with unreachable hop counts immediately to all the nodes in the network ... Some distance-vector routing protocols, such as RIP, use a maximum hop count to determine how many routers traffic must go through to reach the destination ... Each route has a hop count number assigned to it which is incremented as the routing information is passed from router to router ...
IP Traceback - Probabilistic Packet Marking
... suggest encoding the IP address into an 11 bit hash and maintain a 5 bit hop count, both stored in the 16-bit fragment ID field ... This is based on the observation that a 5-bit hop count (32 max hops) is sufficient for almost all Internet routes ... Next, if any given hop decides to mark it first checks the distance field for a 0, which implies that a previous router has already marked it ...

Famous quotes containing the words count and/or hop:

    It may be well to remember that the highest level of moral aspiration recorded in history was reached by a few ancient Jews—Micah, Isaiah, and the rest—who took no count whatever of what might not happen to them after death. It is not obvious to me why the same point should not by and by be reached by the Gentiles.
    Thomas Henry Huxley (1825–95)

    I have tried being surreal, but my frogs hop right back into their realistic ponds.
    Mason Cooley (b. 1927)