nexthops

Next hop, or nexthop, is a routing term for the next device a packet is forwarded to on the path to its destination. In IP networks, the next hop is typically the IP address of the next router along the route, but it can also be the directly connected interface when the destination is on the same local network.

Routing tables store, for each destination, a next-hop value and an outgoing interface. When a router processes a packet, it matches the destination prefix to a route and forwards the packet toward the specified next hop via the indicated interface. The next-hop resolution layer uses ARP in IPv4 or Neighbor Discovery in IPv6 to determine the data-link address of the next hop.

Next hops are determined by static configuration or dynamic routing protocols. Static routes specify a fixed next hop and interface. Dynamic routing protocols such as OSPF, IS-IS, or BGP exchange topology information and metrics to select a best next hop. In networks that support multiple equal-cost paths, ECMP can use more than one next hop to load-balance traffic.

In some protocols the next hop is an attribute that may be modified by policy, such as BGP’s next-hop attribute, or by route synthesis in recursive lookups. For example, BGP often uses next-hop self to influence reachability of eBGP-learned routes.

A next hop must be reachable for the route to be usable; if the next hop becomes unreachable, the corresponding route is not considered viable. Default or 0/0 routes also specify a next hop to reach all non-local destinations.