Cisco 6503 - Catalyst Firewall Security Sys Біла книга - Сторінка 2

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redundancy. For more detail on high-availability network designs, refer to the white paper, Gigabit Campus Design, at:

http://www.cisco.com/en/US/partner/netsol/ns340/ns394/ns147/ns17/

networking_solutions_white_paper09186a00800a3e0b.shtml

Switch Fabric Module Redundancy

Since its introduction, the Cisco Catalyst 6500 Series has been built on a single 32-Gbps bus switching architecture that

provides the data path for all packets through the system. The Cisco Catalyst 6500 Series includes a 256-Gbps crossbar

switching fabric (the SFM for higher bandwidth capacities and 30+ Mpps of forwarding performance). The SFM is supported

in the Cisco Catalyst 6506 and the Cisco Catalyst 6509 chassis. The SFM2 is essentially the same fabric but designed to work

in all the Cisco Catalyst 6506, 6509, and 6513.

Switching Fabric Failover

The SFM also provides another level of hardware redundancy to the system. The single fabric channel versions of the

fabric-enabled line cards provide a connection to both the switching fabric and the existing system bus backplane. This allows

the Cisco Catalyst 6500 Series to use the SFM as the primary data path between fabric-enabled line cards. In the event that an

SFM fails, the system will fail over to the 32-Gbps bus to ensure that packet switching continues (albeit at the bus capacities

of 15 Mpps throughput and 32-Gbps bandwidth) and the network remains online. Additionally, a Cisco Catalyst 6500 Series

can be conﬁgured with dual SFMs (in slots 5 and 6 of a Catalyst 6506 or Catalyst 6509 or in slots 7 and 8 of a Catalyst 6513),

which provide a third level of fabric redundancy. In this conﬁguration, a failure on the primary fabric module would result in

a switchover to the secondary fabric module for continued operation at 30 Mpps. Also, in the event of further fabric module

failures, the ability to switch over yet again to the system bus would still be available.

Switching Fabric Operation

Different combinations of SFMs, fabric-enabled line cards, and classic line cards in a chassis affect the internal switching

operation, which in turn affects the failover characteristics. This is an important point to understand as fabric-to-fabric or

fabric-to-bus failover scenarios are discussed. When an SFM is installed in a system of only fabric-enabled line cards, the

switching operation is called compact mode. This allows for 32-byte compacted headers (not the entire packet) to be sent

across the bus to the supervisor engine for each forwarding decision. The increase in efﬁciency for this operation allows for

inherent system performance capable of 30 Mpps. The data path for fabric-enabled cards is via the SFM.

If a classic line card is installed in a system with an SFM, the header format on the bus must be compatible with all the line

cards in the system. Because classic line cards do not support compact mode, the fabric-enabled line cards will change their

switching modes to truncated mode. Truncated mode allows the fabric-enabled line card to send packets in a 64-byte

header-only format that the classic line cards can understand. It is very important to note that the truncated mode still uses the

SFM as the data path between fabric-enabled line cards. Although the maximum centralized forwarding performance is 15

Mpps in a system of classic and fabric cards, the switch fabric is still used to provide higher bandwidth to the system. If

fabric-enabled line cards are installed in a system with no SFM, they will operate in ﬂow-through mode even when classic

cards are present. This mode essentially programs the line card to operate in a classic mode whereby the entire packet is sent

across the system bus for a forwarding decision. A system in ﬂow-through mode is capable of switching 15 Mpps and the data

path is via the 32-Gbps bus.

Cisco Systems, Inc.

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