Bridging

About Source Route-Transparent Bridges

Because network topologies have developed in which bridges must be able to handle network trafÞc from end stations which support source routing and others which do not, a hybrid type of bridgeÑSource Route-Transparent (SRT)Ñcombines elements of both bridging methods.

An end stationÕs network drivers can be conÞgured in software to use a bit setting in the source address portion of a data frame to indicate whether the station is to operate in a Source Route or Transparently bridged network environment. The Routing Information Indicator (RII) bit of the source address is set to 1 if the station is to use Source Routing; if the station is to operate in a Transparently bridged environment, the RII bit is left unchanged (i.e., at 0).

Not all end stations in a Token Ring environment have network drivers which support Source RoutingÑwhether the drivers are improperly conÞgured via management or they simply are not source-route capable.

In a network with a mix of Source Route and Transparent end stations, data frames from both station types must be bridged correctly. An SRT bridge inspects the RII bit setting of incoming frames to determine whether they should be Transparently bridged (if the RII bit was at 0) or Source Routed (if the RII bit was set to 1) to their destination and will use the appropriate bridge method to forward the frame.

NOTE

Cabletron has extended the functionality of Ethernet ports on translational bridges, so the ports can be set to Source Route mode.

When an Ethernet port is in Source Route mode, on receipt of an SR packet from a Token Ring port, it will save the Source Routing information and send out the packet transparently. When the response comes back, the source routing information will be restored and sent to the Token Ring port.

About Source Route-Translational Bridges

Because SmartSwitch 2000, 6000 and 9000 modules have the ability to combine mixed network topologies, yet another hybrid bridge methodÑcalled a Source Route Translational bridge (SR-TB)Ñis used by a number of these SmartSwitch modules.

An SR-TB bridge supports both Source Routing and Transparent bridging capabilities, with the added requirement of maintaining Source Route information across an FDDI interfaceÑeither the SmartSwitch 9000 FNB backplane, or an installed FDDI High Speed Interface Module (HSIM).

An SR-TB bridge does this by ÒtranslatingÓ the Token Ring physical frame format (by stripping out routing information, if necessary) so that the frameÕs source address can be recognized on an FDDI, Ethernet, or ATM segment; and then, when data is returned to the source, restoring the necessary route information to forward it along a bridged Token Ring environment.

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Bridging Basics

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Cabletron Systems CSX400, CSX200 manual About Source Route-Transparent Bridges, About Source Route-Translational Bridges
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CSX200, CSX400 specifications

Cabletron Systems was a leading developer of networking solutions, and its CSX400 and CSX200 series of high-performance switches represent some of the key innovations in the field of enterprise networking during their time. Both models were geared towards enhancing network reliability, efficiency, and speed, particularly in environments where heavy data traffic and complex networking demands were prevalent.

The CSX400, designed for larger enterprises, boasts a robust architecture capable of handling significant throughput. One of its standout features is its stackable design, allowing multiple switches to be interconnected and managed seamlessly as a single unit. This scalability provides organizations with the flexibility to expand their networks without significant infrastructure overhauls. The CSX400 supports various Ethernet standards, including 10/100 Ethernet and Gigabit Ethernet, positioning it to effectively manage both legacy and modern networking requirements.

In addition to its scalability, the CSX400 is distinguished by its advanced Layer 2 and Layer 3 routing capabilities. This dual-layer functionality enables efficient data handling and is instrumental in managing traffic between different network segments. Moreover, the switch incorporates features like VLAN (Virtual Local Area Network) support and Quality of Service (QoS) prioritization, allowing for enhanced performance of critical applications and streamlined bandwidth allocation.

On the other hand, the CSX200 series is tailored for smaller enterprises or branch offices needing a reliable yet efficient networking solution. Despite its compact design, the CSX200 is equipped with essential features that promote effective network management and security. It offers a simplified management interface, making it user-friendly for network administrators. The switch also provides essential access control measures, employing technologies like IEEE 802.1X for network access security.

Both the CSX400 and CSX200 prioritize performance through the incorporation of advanced switching technologies. They support features such as Spanning Tree Protocol (STP), enabling loop-free topologies and enhanced network resilience. These attributes are particularly crucial in dynamic networking environments where downtime can have significant repercussions on business operations.

Overall, Cabletron Systems' CSX400 and CSX200 series represent a blend of scalability, advanced routing capabilities, and user-friendly management, making them vital assets for organizations looking to optimize their network infrastructure during a period of rapid technological evolution. With their rich feature sets and unwavering performance, these switches helped pave the way for modern networking solutions that cater to diverse enterprise needs.
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