Introduction
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RIP/X Broadcasts
A RIP broadcast is sent out by IPX routers every 30 seconds or so. Each broadcast may contain information on up
to 15 different routes (to 15 different networks). If a router knows of more than 15 networks it will send out two (or
more) broadcasts.
Note that to spread the network overhead a router will stagger the generation of RIP/X and SAP broadcasts. The
router will send a RIP/X broadcast, followed 15 seconds later by a SAP broadcast, followed 15 seconds later by
another RIP/X broadcast, etc., etc. The SAP and RIP/X broadcasts are sent every 30 seconds as required, but they
are staggered by 15 seconds to spread the overhead.
RIP/X Requests
A Client may also request a route to a given network or server. To do so, the Client generates a Route Request
broadcast that the routers hear, and routers that know of the route requested will respond to the originating station.
In this way a new Client may find routes without waiting for the routers’ broadcast, that could be up to 30 seconds
away (if it just missed one). A new router on a network will also broadcast a general Route Request to fill its route
tables quickly. Again, without this mechanism the router would have to wait for about 30 seconds until it heard from
all other routers via their standard RIP/X broadcasts.
RIP/X Metrics
The RIP/X routing protocol measures routes based on two metrics, the hop count and the ticks delay. These metrics
are used to compare different routes to the same network, with the goal of selecting the best (shortest) route.
The ticks delay is the primary metric used to determine the optimal route. The tick count is an indicator of how long
a packet will take to get to the destination. Novell has defined 1 tick to be the length of time it takes a 512-byte frame
to be transmitted on a 10-Mbps (Ethernet) LAN. This works out to about 18 ms. The real value of the tick delay is
when evaluating routes across WAN connections. In these cases, the tick count is dependent on the link speed of the
WAN connection(s), where a slower link will have a higher tick count.
The hop count is the secondary measure of the length of a route; it is exactly the same as the IP hop count. If a route
goes through 1 router (the shortest route), it will have a hop count of 1. If a route goes through 6 routers, the hop
count for that route will be 6. The maximum number of hops RIP/X supports is 15, but this is a very large number,
considering the size of most internetworks. When two or more routes to the same network have the same tick count,
the router will use the route with the smallest hop count.
