CISCO WS-X3500-XL Gigastack GBIC REF

Cisco Systems GigaStack Gigabit Interface Converter

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The Cisco Systems GigaStack® Gigabit Interface Converter (GBIC) is a versatile, low-cost, Gigabit Ethernet stacking GBIC that offers high-speed interconnectivity between Catalyst® 3550, 2950G, 3500 XL and modular Catalyst 2900 XL Switches.

The GigaStack GBIC is implemented in a standard GBIC form, which offers customers the highest level of deployment flexibility and scalability?using available Gigabit Ethernet GBIC ports for high-performance stacking today while preserving the option to migrate to standard Gigabit Ethernet uplinks tomorrow.

Figure 1   The two-port GigaStack GBIC delivers high-speed interconnectivity for stacking connections

The GigaStack GBIC offers wiring closet deployment flexibility through its dual operating modes. It delivers a 1-Gbps forwarding rate in a half-duplex cascade configuration or up to 2-Gbps full-duplex connectivity in a dedicated, switch-to-switch configuration. The two-port GigaStack GBIC allows customers to deploy the GigaStack GBIC with various performance and cabling options. Customers can initially deploy the low-cost GigaStack GBIC to create a 1-Gbps independent stack backplane in a cascade configuration. At any point, customers may increase stack performance to 12 Gbps using the same GigaStack GBICs in combination with the high- performance Catalyst 3550-12G Gigabit Ethernet aggregation switch.

Half-Duplex Configuration Options

Using both ports of each GigaStack GBIC, users can implement a half-duplex cascade of up to nine switches. In this configuration, the GigaStack GBIC will create a half-duplex repeater bus external to the switch fabric of connected switches. This means that traffic bound from one switch to another will not traverse the switch fabric of intermediate switches. Support for nine switches in a single GigaStack stack offers significant wiring-closet port growth opportunities up to a maximum of 432 10/100 ports per stack.

Customers can choose to implement various stackwide physical redundancy options to provide the highest levels of resiliency. For example, users can choose to deploy a 1-meter redundant loopback cable and a second GigaStack GBIC in the top and bottom stack members. This will create a secondary failover connection in the rare case that a stack member or stack cable fails. Alternatively, users can choose to deploy a 1-meter redundant loopback cable attached to the unused GigaStack ports in the top and bottom stack members. New switch cluster command management redundancy features enable the switches to achieve the highest levels of system resiliency.

Figure 2 illustrates a switch stack combined with the GigaStack GBIC half-duplex cascade feature. This configuration depicts a stack of Catalyst 3550 switches and is suitable for those who recognize the need for Gigabit Ethernet uplinks today. In this scenario, connection redundancy is ensured via the redundant loopback cable attached to the top and bottom switches in the stack.

Figure 2   Half-Duplex GigaStack Cascade Configuration

Figure 3 illustrates how the Catalyst 2912MF XL or Catalyst 2924M XL switch can be used in combination with Catalyst 3550, 2950G, or 3500 XL switches using the GigaStack GBIC half-duplex cascade feature. This configuration will provide the flexibility to implement a migration plan from legacy uplink connections to Gigabit Ethernet in the future. For example, each Catalyst 2924M XL switch may initially be used to support 100BASE-FX or ATM uplinks while still maintaining the full capabilities of Gigabit Ethernet stacking and compatibility with Cisco Switch Clustering Management. At any subsequent time, Catalyst 3550 or 2950G switches may be used to support a migration plan to Gigabit Ethernet fiber uplinks.

Figure 3   Half-Duplex GigaStack Cascade Configuration with Legacy Uplink Migration Flexibility

Full-Duplex Configuration Options

Customers can also use the GigaStack GBIC to create a low-cost dedicated Gigabit Ethernet connection between two stack members, providing a scalability option to increase overall stack bandwidth. When connecting two GigaStack GBICs with a single cable, the GBIC will autonegotiate to full-duplex and provide a 1-Gbps forwarding rate in each direction?or 2 Gbps. By simply changing the stack configuration from a cascade to a star configuration, customers can provide dedicated Gigabit Ethernet connectivity to each stack member. When combined with a Catalyst 3550-12G Gigabit Ethernet aggregation switch, this solution offers a very high-performance migration path. The Catalyst 3550-12G can provide stack aggregation with Gigabit Ethernet port connectivity.

Users can also choose to implement higher levels of resiliency in their full-duplex GigaStack configurations. High levels of redundancy can be implemented within the wiring closet stack and on the network core uplinks. Within the wiring closet, a second Catalyst 3550-12T or 3550-12G aggregation switch can be deployed with redundant links to each stack member. And, redundant uplinks can be deployed from the distribution layer to the network core. When deploying redundant gigabit uplinks, users can benefit from link failover times that are significantly shorter than standard Spanning Tree Protocols. By implementing the Cisco UplinkFast feature, failover can be minimized to as little as 1 to 2 seconds. In addition, the Cisco Per-VLAN Spanning Tree Plus (PVST+) feature can be deployed to ensure that all redundant uplinks perform load balancing. In other words, all redundant uplinks are active and carry traffic.

Users can achieve even higher levels of performance in their full-duplex stacks by configuring dual links from an aggregation switch to each stack member. The two Gigabit Ethernet ports on each Catalyst 3550 Series switch can be grouped together using Gigabit EtherChannel® technology to create a stack connection with a full-duplex 4-Gbps forwarding rate.

Figure 4 illustrates a switch stack configured with GigaStack GBICs operating in full-duplex mode. In this configuration, the Catalyst 3550-12G Gigabit Ethernet switch creates a high-performance option for switch aggregation using point-to-point links. Fault tolerance is implemented via a redundant Catalyst 3550-12G switch. High-speed uplinks from the Catalyst 3550-12G switch to the network core are provided via Gigabit EtherChannel technology.

Figure 4   Full-Duplex GigaStack Star Configuration

Full Compatibility with Cisco Switch Clustering Management Technology

Users can choose to deploy GigaStack GBIC stacking while benefiting from the powerful multidevice management technology available in Cisco Switch Clustering technology. Switch Clustering technology allows customers to manage a stack of devices within a wiring closet or a broadly dispersed set of devices across a campus as a single IP entity. Switch Clustering technology uses standard TCP/IP packets to distribute and collect management information for all switches in the cluster. Switch Clustering supports a broad range of physical interconnections, including the GigaStack GBIC.

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