In wired

computer networking A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

, including the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

, a hop occurs when a packet is passed from one

network segment A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations. Ethernet According to the defining IEEE 802.3 standards ...

to the next. Data packets pass through routers as they travel between source and destination. The hop count refers to the number of network devices through which data passes from source to destination (depending on routing protocol, this may include the source/destination, that is, the first hop is counted as hop 0 or hop 1). Since

store and forward Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in ...

and other latencies are incurred through each hop, a large number of hops between source and destination implies lower

real-time Real-time or real time describes various operations in computing or other processes that must guarantee response times within a specified time (deadline), usually a relatively short time. A real-time process is generally one that happens in defined ...

performance.

Hop count

In wired networks, the hop count refers to the number of networks or network devices through which data passes between source and destination (depending on routing protocol, this may include the source/destination, that is, the first hop is counted as hop 0 or hop 1). Thus, hop count is a rough measure of distance between two hosts. For a routing protocol using 1-origin hop counts (such as RIP), a hop count of ''n'' means that ''n'' networks separate the source host from the destination host. Other protocols such as DHCP use the term "hop" to refer to the number of times a message has been forwarded. On a

layer 3 In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of transfe ...

network such as

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

(IP), each router along the data path constitutes a hop. By itself, this metric is, however, not useful for determining the optimum network path, as it does not take into consideration the

speed In everyday use and in kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (ma ...

, load, reliability, or latency of any particular hop, but merely the total count. Nevertheless, some

routing protocol A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets ...

s, such as

Routing Information Protocol The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from sour ...

(RIP), use hop count as their sole

metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathem ...

. Each time a router receives a packet, it modifies the packet, decrementing the

time to live Time to live (TTL) or hop limit is a mechanism which limits the lifespan or lifetime of data in a computer or network. TTL may be implemented as a counter or timestamp attached to or embedded in the data. Once the prescribed event count or times ...

(TTL). The router discards any packets received with a zero TTL value. This prevents packets from endlessly bouncing around the network in the event of routing errors. Routers are capable of managing hop counts, but other types of network devices (e.g.

Ethernet hub An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/out ...

s and

bridges A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually someth ...

) are not.

Hop limit

Known as ''

'' (TTL) in IPv4, and '' hop limit'' in

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...

, this field specifies a limit on the number of hops a packet is allowed before being discarded. Routers modify IP packets as they are forwarded, decrementing the respective TTL or hop limit fields. Routers do not forward packets with a resultant field of 0 or less. This prevents packets from following a loop forever.

Next hop

When configuring network devices the ''hop'' may refer to ''next hop''. Next hop is the next gateway to which packets should be forwarded along the path to their final destination. A

routing table In computer networking, a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with th ...

usually contains the

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

of a destination network and the IP address of the next gateway along the path to the final network destination. By only storing next-hop information, ''next-hop routing'' or ''next-hop forwarding'' reduces the size of routing tables. A given gateway only knows one step along the path, not the complete path to a destination. It is also key to know that the next hops listed in a routing table are on networks to which the gateway is directly connected .

Diagnostics

The

traceroute In computing, traceroute and tracert are computer network diagnostic commands for displaying possible routes (paths) and measuring transit delays of packets across an Internet Protocol (IP) network. The history of the route is recorded as th ...

command can be used to measure the number of router hops from one host to another. Hop counts are often useful to find faults in a network or to discover if routing is indeed correct.

Wireless ad hoc networking

In a

wireless ad hoc network A wireless ad hoc network (WANET) or mobile ad hoc network (MANET) is a decentralized type of wireless network. The network is ad hoc because it does not rely on a pre-existing infrastructure, such as routers in wired networks or access points ...

, commonly, every participating node is also acting as a router. This means that the terms "hop" and "hop count" are often the subject of confusion. Often, the sending node is simply counted as the first hop, thus yielding the same number for "hops" for both interpretations of "hop" as "traversed routers" and "jumps from node to node". For example, RFC 6130 defines a "1-hop neighbor" as any other node that is directly reachable via the wireless interface.

References