RIPv1

RIPv1, or Routing Information Protocol Version 1, is the original version of the Routing Information Protocol designed for IPv4 networks. It operates as a distance-vector routing protocol, in which routers periodically exchange entire routing tables with their neighbors to determine paths to destinations.

RIPv1 uses hop count as its routing metric, with a maximum of 15 hops allowed. A route with a hop count of 16 is considered unreachable. Updates are sent at regular intervals, historically every 30 seconds, and are distributed by broadcast to neighboring routers. Updates use UDP and typically travel on port 520, broadcast to the local network address 255.255.255.255.

A defining characteristic of RIPv1 is its classful routing behavior. It does not carry subnet masks in its updates, so routers must assume the default classful mask for each destination. This limitation makes RIPv1 unable to support variable-length subnet masks (VLSM) or discontiguous networks, and can lead to routing inefficiencies or errors in networks that employ subnetting.

RIPv1 provides no built-in authentication mechanism in its original form, which lowers security for routing information. Its simplicity and limitations contributed to it being largely superseded by later protocols and network designs. Nevertheless, it served as an early, practical solution for small to medium-sized IPv4 networks and informed the development of more advanced protocols such as RIPv2.

Historically, RIPv1 was standardized in RFC 1058 (1988). In modern practice, it has largely been replaced by RIPv2 and by other distance-vector or link-state protocols, though it may still appear in legacy environments.