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This chapter contains the following information about the Catalyst 3900:
The Catalyst 3900 is a stackable Token Ring switch that provides the following:
The Catalyst 3900 can be used as a standalone switch, or it can be interconnected with up to seven other switches in a ProStack configuration. The ProStack system is formed by connecting two to eight switches with SCSI II-type cables via a ProStack Matrix crossbar switch. A two-switch ProStack may be formed by directly connecting two switches.
In addition, two switches may be interconnected by a number of parallel Token Ring connections, called TokenChannels. A TokenChannel is two to eight parallel links between Catalyst 3900 switches. The traffic between the switches is shared via the connections.
For more information about stacking Catalyst switches and using TokenChannels, refer to the "Interconnecting Catalyst 3900 Switches" chapter.
The Catalyst 3900 supports the following bridging and switching modes:
For more information about these bridging modes, refer to the "Understanding Token Ring Switching" appendix.
Each of the 20 Token Ring ports can operate in one of the following modes:
The mode of operation can be configured, or it can be automatically sensed when equipment is connected to the port. The media speed (4 or 16 Mbps) can also be configured or automatically sensed in all port modes.
A loopback function has been implemented on ports 19 and 20 so that if the port is disabled or the switch is powered off there will not be a break in the attached main ring. This function means that attaching a cable from the RI port of a MAU port to one of the two switch ports in effect joins the primary and the backup ring in a MAU/CAU main ring system. Connecting the other end of the main ring to the other switch port creates redundant paths because the two switch ports are connected to the same segment. Therefore, the Spanning-Tree Protocol must be enabled, which will place one port in forward mode and the other in blocked mode. If there is a break in the main ring, the Spanning-Tree Protocol will place both ports in forward mode, and all MAC addresses on both segments will be relearned.
The queue for a frame is determined by the value of the priority field in the frame control (FC) byte of the frame. If FC priority is above a configurable level (the default is 3), the frame is put in the high-priority queue. If an output port becomes congested, you can dynamically configure the port to transmit all frames at high priority regardless of the FC byte contents.
The Catalyst 3900 CPU software monitors the size of the output queue at each Token Ring port to minimize the effects of congestion at output ports. When port congestion is detected, the Catalyst 3900 does the following:
MAC address filters and broadcast filters can be applied only at input ports. DSAP and SNAP filters can be applied at input ports and output ports.
The Catalyst 3900 is also notified when a Token Ring beacon state is detected on the ring and when it disappears. If the beacon state remains for more than a specified amount of time, the port is instructed to discard all frames in the output queue and to reject new frames. When the beacon state disappears, the port is instructed to once again accept frames.
The CDP support allows the Catalyst 3900 to establish communication with other models of Cisco equipment. CDP support is provided as part of the Cisco IOS software that runs on many types of Cisco equipment.
CDP is a media- and protocol-independent protocol that is intended to be run on Cisco-manufactured equipment including routers, bridges, access servers, and switches. With CDP, Cisco's network management applications and Cisco devices can learn the device type and the SNMP agent address of neighboring devices. This enables applications to send SNMP queries to neighboring devices.
CDP runs on various media that support the SNAP, including LAN, Frame Relay, and Asynchronous Transfer Mode (ATM) media. CDP runs over the data link layer only. Therefore, two systems that support different network-layer protocols can learn about each other.
Each device configured for CDP sends periodic messages to a multicast address. Each device advertises at least one address at which it can receive SNMP messages. The advertisements also contain time-to-live, or holdtime, information, which indicates the length of time a receiving device should hold CDP information before discarding it.
There are two levels of VLANs supported by the Catalyst 3900. The first level is the Token Ring Concentrator Relay Function (TrCRF). This is the level of VLAN to which the ports are assigned. The second level is the Token Ring Bridge Relay Function (TrBRF). This is the parent VLAN to which TrCRF VLANs are assigned. Traffic is switched between ports in a TrCRF and bridged between TrCRFs in a TrBRF. The Catalyst 3900 maintains certain configuration information and management statistics on a per VLAN basis. Therefore, when you access VLAN-specific Catalyst 3900 configuration or management panels (such as the Current Spanning Tree Information panel), you will be prompted to specify the desired TrBRF or TrCRF.
The Catalyst 3900 provides a series of menu-driven configuration and management panels that you can access via a connected terminal attached to the EIA 232 management port, or from a remote terminal via Telnet. Up to five Telnet sessions are permitted at any one time. In addition, you can do the following:
The Catalyst 3900 can be managed via an SNMP manager. The Catalyst 3900 supports twelve Management Information Bases (MIBs). Nine of the MIBs are standard MIBs, which are defined by RFCs and are included with most SNMP management applications. Three of the MIBs are private MIBs and can be obtained from CCO.
The standard MIBs supported are:
The private MIBs supported are:
Most user configurable variables are supported in either the standard MIBs or private MIBs. Configuration settings, such as port attributes, and operational information, such as address tables, are fully accessible through SNMP. Certain other settings, such as passwords and console settings, cannot be viewed or modified via SNMP for security reasons.
RMON is an industry-standard method for providing network statistics monitoring using SNMP. It also collects fault, performance, and configuration statistics. RMON can monitor continuously, even when communication with the management station is not possible or efficient. It can then notify the management station when an exceptional condition occurs.
In typical SNMP management, the SNMP client has to continuously poll the Catalyst 3900 for fault, performance, and configuration information while waiting for the value to change. This causes increased traffic through the network. With RMON, you can have the switch monitor a particular statistic internally, and when the statistic reaches a threshold, the Catalyst 3900 will send a trap to the client. This monitoring method reduces traffic between the SNMP client and the Catalyst 3900 switch.
As an option, the Catalyst 3900 provides RMON support statistics, history, alarms, and events. It also provides support for the following groups of the Token Ring extensions to the Remote Network Monitoring MIB (RFC 1513):
You can use an external RMON probe for full RMON support.
Access to RMON data is available only via an SNMP management application that supports RFC 1757 and RFC 1513. You cannot access RMON via the Catalyst 3900 console interface; however, the console statistics provide similar information. For full utilization of RMON data, you should use Cisco's TrafficDirector.
To aid in network management, the Catalyst 3900 allows you to copy traffic from any Token Ring port to the Switched Port Analyzer (SPAN) port. You can then attach an external Token Ring monitor (network analyzer) or RMON probe to the SPAN port. Forwarding to the SPAN port takes place independently of the normal forwarding.
The Catalyst 3900 has a CPU planar board with 20 RJ-45 Token Ring ports, two adapter expansion slots, one ProStack port, and one RS-232 port for management and configuration. Figure 1-1 shows the front of the Catalyst 3900.
This 9-pin, male, management port functions as a data terminal equipment (DTE) port.
This port enables attachment of a terminal or terminal emulator that is used to customize the configuration of the switch, monitor switch activity and status, and test the switch. Console access can be either local, by direct attachment to the EIA 232 port, or remote, through a modem connection.
The EIA 232 port automatically detects the baud rate of the terminal to which it is attached.
 | Caution If this button is pressed for longer than 5 seconds, a download of the main image will be forced. This function should be used only at the direction of service personnel. The button is recessed to prevent accidental activation. |
The power connector is located on the back of the Catalyst 3900. There is no power switch.
The program memory dynamic random-access memory (DRAM) is used for program and data storage. It consists of four banks of DRAM providing up to 8 MB of storage.
The Proprietary Fat Pipe is the interface to a ProStack port. The ProStack port operates in FDX mode at speeds of 140 Mbps. It switches packets at wire speeds with low forwarding latency. A proprietary 4-byte header is used to allow the members of the stack to function as one operational system.
Posted: Wed Oct 2 02:53:25 PDT 2002
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