5-4CHAPTER 5: CONFIGURING THE TR-IN-FE MODULE
Ports with a lower value have a higher priority and will be blocked only after ports with a higher value and a lower priority have been blocked.
■Path Cost—Path cost determines the amount of overhead required to forward packets to the root through this port.
The higher the path cost, the less likely Spanning Tree will use a port for forwarding. The lower the cost, the more likely Spanning Tree will use a port for forwarding.
NOTE: It is always recommended that, in the case of a loop formed with a low speed port, the high-speed ports do not block. The switch automatically provides this function with default settings (port speed is part of the spanning tree calculations). Be aware of this, if the spanning tree values are modified.
■Fast Fwd—Frames are forwarded as soon as the destination address is received and verified.
Source Routing
Source Routing is a method of allowing a ring station (node) on a Token Ring network to communicate with another ring station on a different ring intercon- nected by bridges. The “source” ring station, which is the node initiating the communication, is responsible for dynamically determining and then maintaining information about the “route” to the destination ring station. A route is simply the path a packet takes through a source route bridged network from the source ring station to the destination ring station.
In the case of TR-in-FE, a virtual LAN ID must be assigned to the FE cloud. This allows Source Routing to proceed as though the FE media supported TR natively. The entire FE transparently forwarded cloud appears as a single “ring” and hence a single hop to attached TR endstations. This also allows FE servers to participate in source routing.
■Attached Lan Id—A unique number that identi- fies the segment to which the port connects. This value can be set between 0 and FFF (0-4095). A value of FFFF (65535) indicates that no segment number has been assigned to this port.
■Max Route-Desc—This value describes the number of routing descriptions allowed in All Route Explorer (ARE) or Spanning Tree Explorer (STE) frames. This is also referred to as “hop count” limit since it limits the number of rings a packet can traverse.
■STE Mode—This value determines how this port responds when presented with Spanning Tree Explorer (STE) packets. Set the field accordingly by pressing the [Space Bar].
■Disabled—Indicates that the port will not accept or propagate STE packets, and any pack- ets received will be discarded.
■Forced—Indicates that the port will always accept and propagate STE packets.
■Auto-Span—Indicates that the port will accept and propagate STE packets when its Spanning Tree state is forwarding.
