HP VPN Firewall Appliances Appendix Protocol Reference

6
RIP
The term "router" in this document refers to both routers and routing-capable firewalls and firewall
modules.
Routing Information Protocol (RIP) is a distance-vector simple interior gateway protocol suited to
small-sized networks. It employs UDP to exchange route information through port 520.
Overview
RIP uses a hop count to measure the distance to a destination. The hop count from a router to a directly
connected network is 0. The hop count from a router to a directly connected router is 1. To limit
convergence time, RIP restricts the metric range from 0 to 15. A destination of a metric value of 16 (or
greater) is considered unreachable. For this reason, RIP is not suitable for large-sized networks.
RIP route entries
RIP stores routing entries in a database. Each routing entry contains the following elements:
• Destination address—IP address of a destination host or a network.
• Next hop—IP address of the next hop.
• Egress interface—Egress interface of the route.
• Metric—Cost from the local router to the destination.
• Route time—Time elapsed since the last update. The time is reset to 0 every time the routing entry
is updated.
• Route tag—Used for route control. For more information, see Network Management Configuration
Guide.
RIP timers
RIP uses the following timers:
• Update timer—Specifies the interval between route updates.
• Timeout timer—Specifies the route aging time. If no update for a route is received within the aging
time, the metric of the route is set to 16.
• Suppress timer—Specifies the duration a RIP route stays in suppressed state. When the metric of a
route is 16, the route enters the suppressed state. A suppressed route can be replaced by an
updated route that is received from the same neighbor before the suppress timer expires and has a
metric less than 16.
• Garbage-collect timer—Specifies the interval from when the metric of a route becomes 16 to when
it is deleted from the routing table. RIP advertises the route with a metric of 16. If no update is
announced for that route before the garbage-collect timer expires, the route is deleted from the
routing table.