How to Convert Native 40G Ports to 8x10G Ports in Catalyst 6840-X?

The Catalyst 6840-X-LE-40G and 6824-X-LE-40G have two native 40-Gb ports.

These ports can be converted to 8x10G ports, starting from Cisco IOS Software Release 15.2(2) SY2, by simply changing the operation mode from ‘FortyGigabitEthernet mode’ to ‘TenGigabitEthernet mode’. The following output provides an example.

Note: Changing the operation mode will reset the whole chassis; all 40G ports configuration will be lost.

C6840-X-LE#sh hw-module slot 1 operation mode 

Module 1 port group 1 is running in TenGigabitEthernet mode

Module 1 port group 2 is running in TenGigabitEthernet mode

Module 1 port group 3 is running in TenGigabitEthernet mode

Module 1 port group 4 is running in TenGigabitEthernet mode

Module 1 port group 5 is running in TenGigabitEthernet mode

Module 1 port group 6 is running in FortyGigabitEthernet mode C6840-X-LE#

C6840-X-LE#conf t

Enter configuration commands, one per line. End with CNTL/Z.

C6840-X-LE(config)#hw-module slot 1 operation-mode port-group 6 TenGigabitEthernet 

Operation mode change will reset the whole SUP and all the ports config will be lost. Do you want to continue with reset? [confirm]

Building configuration...

[OK]

*Mar 11 17:53:10.491: %SYS-5-RELOAD: Reload requested by Exec. Reload Reason: TFR SKU OPMODE CHANGE.

C6840-X-LE#show ip interface brief

Interface IP-Address OK? Method Status Protocol

TenGigabitEthernet1/40 unassigned YES NVRAM administratively down down

TenGigabitEthernet1/43 unassigned YES unset up up

TenGigabitEthernet1/44 unassigned YES unset up up

TenGigabitEthernet1/45 unassigned YES unset up up

TenGigabitEthernet1/46 unassigned YES unset up up

TenGigabitEthernet1/47 unassigned YES unset up up

TenGigabitEthernet1/48 unassigned YES unset up up

TenGigabitEthernet1/49 unassigned YES unset up up

TenGigabitEthernet1/50 unassigned YES unset up up
Performance Mode

The Cisco Catalyst 6840-X Series has two performance modes: oversubscription mode and performance mode.

Note that these modes affect port groups rather than an individual port.

By default, the module operates in oversubscription mode since a backplane capacity of 80 GB per DFC4-E feeds 16×10 Gigabit Ethernet ports, resulting in a 2:1 oversubscription ratio.

The default port performance mode can be identified using a show command:

C6816-X-LE#sh hw-module slot 1 operation mode 

Module 1 port group 1 is running in TenGigabitEthernet mode

Module 1 port group 2 is running in TenGigabitEthernet mode

C6816-X-LE#sh hw-module slot 1 oversubscription 

port-group oversubscription-mode

1 enabled

2 enabled

Performance mode can be enabled by issuing a configuration command that will result in shutting down certain ports in the selected port group so as to make the port-to-fabric bandwidth come down from 2:1 to 1:1. The second half of the port group will be disabled when configuring performance mode. (for instance, configuring port group 2 on the Catalyst 6816-X-LE will disable ports 13, 14, 15, and 16, and will be available on ports 9, 10, 11, and 12. The ratio will be a 1:1 port-to-fabric bandwidth.

C6816-X-LE#conf t

Enter configuration commands, one per line. End with CNTL/Z.

C6816-X-LE(config)#no hw-module slot 1 oversubscription port-group 2 

WARNING: Switch to TRANSPARENT mode on module 1 port-group 2.

*Apr 28 17:13:22.989: %C6K_PLATFORM-6-NON_OVERSUBSCRIPTION_TEN_GIG: Ports 13, 14, 15, 16, of slot 1 disabled to prevent module bandwidth oversubscription.

C6816-X-LE#sh hw-module slot 1 oversubscription 

port-group oversubscription-mode

1 enabled

2 disabled

The Catalyst 6840-X series chassis provides extremely high levels of scalability and performance, with the size and economics of an innovative fixed architecture. This unique platform offers 10-Gb port density; full IPv4/IPv6 and MPLS/VPLS functionality with large table sizes (up to 256,000 Forwarding Information Base [FIB] entries); and more than 15 years of best-in-class features.

With a full suite of Layer 2 and 3, virtualization, security, multicast, IPv6, application visibility, smart operations, and rich media services, the Cisco Catalyst 6840-X delivers superior capabilities from its first day of deployment.

More info from https://www.cisco.com/c/dam/en/us/products/collateral/switches/catalyst-6800-series-switches/white-paper-c11-737288.pdf

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