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The Cisco Catalyst 6500 is a modular chassis network switch manufactured by Cisco Systems since 1999, capable of delivering speeds of up to "400 million packets per second". A Catalyst 6500 is made up of a chassis, power supplies, one or two supervisor engines, line cards and service modules. These Catalyst chassis can have 3, 4, 6, 9 or 13 slots each (Variations of the Cisco Catalyst models include 6503, 6504, 6506, 6509, or 6513, respectively) with the option of one or two modular power supplies. The supervisor engine provides centralised forwarding information and processing; up to two of these cards can be installed in a chassis to provide active/standby or stateful failover. Cisco line cards provide port connectivity and Cisco service modules to allow for devices such as firewalls to be integrated within the switch.

Supervisor Engine is Vital for Cisco 6500 Series

The 6500 Supervisor is composed of a Multilayer Switch Feature Card (MSFC) and a Policy Feature Card (PFC). The MSFC runs all software processes, such as routing protocols. The PFC makes forwarding decisions for the Cisco switch. The supervisor also includes bootflash for the Cisco IOS software, a connection to the switching fabric and classic bus.

Understanding Cisco Operating Systems

There are 3 total operating systems supported in this series.

CatOS

CatOS is supported for layer 2 (switching) operations only. To be able to perform routing functions (e.g. Layer 3) operations, the switch must be run in hybrid mode. In this case, CatOS runs on the Switch Processor (SP) portion of the Supervisor, and IOS runs on the Route Processor (RP) also known as the MSFC. To make configuration changes, the user must then manually switch between the two environments. While CatOS does have some functionality missing, it's generally considered obsolete compared to running a switch in Native Mode.

Native IOS

Cisco IOS can be run on both the SP and RP. In this instance, the user is unaware of where a command is being executed on the switch, even though technically two IOS images are loaded -- one on each processor. This mode is the default shipping mode for Cisco products and enjoys support of all new features and line cards.

Modular IOS

Modular IOS is a version of Cisco IOS that employs a modern UNIX-based kernel to overcome some of the limitations of IOS. Additional to this is the ability to perform patching of processes without rebooting the device and in service upgrades.

Operational Methods

The Cat 6500 has 5 major modes of operation: Classic, cef256, dcef256, cef720 and dcef720.

Classic Bus

The Cisco 6500 classic architecture provides 32 Gbit/s centralised forwarding performance. The design is such that an incoming packet is first queued on the line card and then placed on to the global data bus (dBus) and is copied to all other line cards, including the supervisor. The supervisor then looks up the correct egress port, access lists, policing and any relevant rewrite information on the PFC. This is placed on the result bus (rBus) and sent to all line cards. Those line cards for whom the data is not required terminate processing. The others continue forwarding and apply relevant egress queuing.

The speed of the classic bus is 32gb half duplex (since it's a shared bus) and is the only supported way of connecting a Supervisor 32 engine (or Supervisor 1) to a 6500.

cef256

This method of forwarding was first introduced with the Supervisor 2 engine. When used in combination with a switch fabric module, each line card has an 8gb connections to the switch fabric and additionally a connection to the classic bus. In this mode, assuming all line cards have a switch fabric connection, an ingress packet is queued as before and its headers are sent along the dBus to the supervisor. They are looked up in the PFC (including ACLs etc) and then the result is placed on the rBus. The initial egress line card takes this information and forwards the data to the correct line card along the switch fabric. The main advantage here is that there is a dedicated 8 Gbit/s connection between the line cards. The receiving line card queues the egress packet before sending it from the desired port.

The '256' is derived from a chassis using 2x8gb ports on 8 slots of a 6509 chassis: 16 * 8 = 128, 128 * 2 = 256. The number is doubled due to the switch fabric being 'full duplex'.

dcef256

dcef256 uses distributed forwarding. These line cards have 2x8gb connections to the switch fabric and no classic bus connection. Only modules that have a DFC (Distributed Forwarding Card) can use dcef.

Unlike the previous examples, the line cards holds a full copy of the supervisors routing tables locally, as well as its own L2 adjacency table (i.e. MAC addresses). This eliminates the need for any connection to the classic bus or requirement to use the shared resource of the supervisor. In this instance, an ingress packet is queued, but its destination looked up locally. The packet is then sent across the switch fabric, queued in the egress line card before being sent.

cef720

This mode of operation acts identically to cef256, except with 2x20gb connections to the switch fabric and there is no need for a switch fabric module (this is now integrated in to the supervisor). This was first introduced in to the Supervisor Engine 720.

The '720' is derived from a chassis using 2x20gb ports on 9 slots of a 6509 chassis. 40 * 9 = 360 * 2 = 720. The number is doubled to the switch fabric being 'full duplex'. The reason 9 slots are used for the calculation instead of 8 for the cef256 is that it no longer needs to waste a slot with the switch fabric module.

dcef720

This mode of operation acts identically to dcef256, except with 2x20gb connections to the switch fabric.

Cisco 6500 Power Supply Options

The 6500 is able to deliver high densities of Power over Ethernet across the chassis. Due to this, power supplies are a key element of configuration.

Cisco Catalyst 6503 Power Supplies

The original chassis permits up to 4200W (100A @ 42V) and uses rear-inserted power supplies different from the others in the series. With the introduction of the 6503-E, this was increased to 5000W (119A @ 42V).

Cisco Catalyst 6504-E (Enhanced) Power Supplies

This Cisco chassis permits up to 2700W (119A @ 42V) of power and, like the 6503, uses rear-inserted power supplies.

Cisco Catalyst 6506, 6509, 6506-E and 6509-E Power Supplies

The original chassis can support up to a maximum of 4000W (90A @ 42V) of power, due to backplane limitations. If a power supply above this is inserted, it will deliver at full power up to this limitation (i.e. a 6000W power supply is supported in these chassis, but will output a maximum of 4000W). The 6509-NEB-A supports a maximum of 4500W (108A @ 42V). With the introduction of the 6506-E and 6509-E series chassis, the maximum power supported has been increased to in excess of 14500W (350A @ 42V).

Cisco Catalyst 6513 Power Supplies

This chassis can support a maximum of 8000W (180A @ 42V). However, to obtain this, it must be run in combined mode. Therefore, it is suggested that it be run in redundant mode to obtain a maximum of 6000W (145A @ 42V).

Understanding Power Supply Redundancy

The 6500 supports dual power supplies for redundancy. These may be run in one of two modes: redundant or combined mode.

Redundant Mode

When running in Redundant Mode, each power supply provides approximately 50% of its capacity to the chassis. In the event of a failure, the unaffected power supply will then provide 100% of its capacity and an alert will be generated. As there was enough to power the chassis ahead of time, there is no interruption to service in this configuration. This is also the default and recommended way to configure power supplies.

Combined Mode

In combined mode, each power supply provides approximately 83% of its capacity to the chassis. This allows for greater utilisation of the power supplies and potentially increased PoE densities.

In the event of a failure, all devices except the supervisor are powered down. During this time, there will be a temporary network outage while power is returned to the system. The order this is done is:

First service modules, from the top down, are powered up.
Then line cards, from the top most slot to the bottom most, are powered up. PoE is not permitted at this stage.
Next PoE, from the highest line card and the highest port (i.e. line card 0/port 0) down through to the lowest, are powered up.

The above process is done until the maximum power capacity of the remaining power supply is reached. Normally, a single power supply will be able to power all service modules and line cards, but not give the PoE densities required.

Online Insertion & Removal Feature

OIR is a feature of the 6500 allowing hot swapping most line cards without first powering down the chassis. The advantage of this is that one may perform an in-service upgrade. However, before attempting this, it is important to understand the process of OIR and how it may still require a reload.

To prevent bus errors, the chassis has three pins in each slot which correspond with the line card. Upon insertion, the longest of these makes first contact and stalls the bus (to avoid corruption). As the line card is pushed in further, the middle pin makes the data connection. Finally, the shortest pin removes the bus stall and allows the chassis to continue operation.

However, if any part of this operation is skipped, errors will occur (resulting in a stalled bus and ultimately a chassis reload). Common problems include:

Line cards being inserted incorrectly (and thus making contact with only the stall and data pins and thus not releasing the bus)
Line cards being inserted too quickly (and thus the stall removal signal is not received)
Line cards being inserted too slowly (and thus the bus is stalled for too long and forces a reload).

About the Author - Admin: The Admin believes this information on the Cisco 6500 series is highly relevant for a technical administrator to digest before making a purchasing decision.

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