Perle Systems IOLINK-520 Bridging and the IOLINK-PRO & 520 Routers, RIP/X Requests, RIP/X Metrics

Introduction

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.

Bridging and the IOLINK-PRO & 520 Routers

The bridge portion of the IOLINK-PRO & 520 router is an Ethernet Media Access Control (MAC) level bridge providing an efficient means of interconnecting IEEE 802.3 Local Area Networks supporting a choice of standard Ethernet (10Base5), Thin Ethernet (10Base2) and Twisted Pair (10BaseT) interfaces. With the support of these industry-standard LAN interface technologies, the IOLINK-PRO & 520 routers will resolve the media conflicts that might have otherwise prevented the consolidation of these resources.

The IOLINK-PRO & 520 routers will also fit right into those environments that may require more than one bridge by using the IEEE 802.1D Spanning Tree Protocol. With this protocol, the IOLINK-PRO & 520 routers will perform automatic network reconfiguration in the event of a link failure to one of the LAN segments. This provides maximum availability of the attached LAN services.

Immediately following are several short descriptions of LAN bridging operations specific to the IOLINK-PRO & 520 routers. These descriptions will help you understand the concepts of bridging and how the IOLINK-PRO & 520 routers performs these functions.

The remaining sections of this document describe how these functions are performed and configured. You are urged to spend the small amount of time necessary to familiarize yourself with the IOLINK-PRO & 520 router and the advanced functions it may perform for you.

1.12— IOLINK-PRO & 520 Reference Manual