6509 WS-SUP720-3BXL switch fabric

Unanswered Question
Sep 7th, 2010

Hi, recently i notice that one of our 6509 switches was operating in truncated mode when i looked at this i noticed we had an old flexwan connected to the switch that was not being used, after removing it we are now running in compact mode.

before removing the flexwan I was seeing this.

Global switching mode is Truncated
dCEF mode is not enforced for system to operate
Fabric module is not  required for system to operate
Modules are allowed to operate in bus mode
Truncated mode is allowed, due to presence of Standby supervisor module

Module Slot     Switching Mode
    1                 Crossbar
    2                 Crossbar
    5                      Bus
    6                 Crossbar
    8                      Bus (flexwan)

Module 5 is the sup720-3bxl, shouldn't I have been seeing Crossbar on 5 instead of BUS(Flow-Through)?

after removing the old felxwan I now see,

Global switching mode is Compact
dCEF mode is not enforced for system to operate
Fabric module is not  required for system to operate
Modules are allowed to operate in bus mode
Truncated mode is allowed, due to presence of Standby supervisor module

Module Slot     Switching Mode
    1                 Crossbar
    2                 Crossbar
    5                     dCEF
    6                 Crossbar

I guess im not understanding what performance im loosing when i have a classic card installed. For the ouput below with either switching modes I see the same speed.

slot    channel      speed    module               fabric
                                status               status
     1          0         8G        OK                   OK
     2          0         8G        OK                   OK
     5          0        20G        OK                   OK
     6          0         8G        OK                   OK

As I understand it, all non SFM will use the shared 32 Gb bus but how does having a classic card affect the sup720, what performance was lost when i had a none SFM card installed as compared to having all SFM?

thanks, Paul

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
Jon Marshall Wed, 09/08/2010 - 06:47

ra7or wrote:

Hi, recently i notice that one of our 6509 switches was operating in truncated mode when i looked at this i noticed we had an old flexwan connected to the switch that was not being used, after removing it we are now running in compact mode.


As I understand it, all non SFM will use the shared 32 Gb bus but how does having a classic card affect the sup720, what performance was lost when i had a none SFM card installed as compared to having all SFM?

thanks, Paul

Paul

Compact = centralised forwarding of up to 30Mpps

Truncated = centralised forwarding of up to 15Mpps

From the 6500 Architecture White Paper -

Compact Mode

The compact mode of operation requires a crossbar switch fabric to be present in the system. This can be provided by a switch fabric module, Switch Fabric Module 2 or a Supervisor Engine 720. All modules in the chassis must be fabric enabled (i.e. CEF256, dCEF256, or CEF720) for the switch to operate in Compact Mode. Classic line cards installed in the chassis will negate the ability of the switch to run in Compact Mode. In Compact Mode, only the header is passed over the DBus to the supervisor. The Header is compressed prior to being placed on the DBus which increases the bandwidth available for header transmission. The data portion of the packet is transmitted over the crossbar switch fabric channels. In this mode of operation, the switch can achieve centralized performance of up to 30Mpps independent of packet size.

Truncated Mode

Truncated Mode is used when CEF256 and/or CEF720 line cards are installed in a chassis with a classic line card, but a crossbar switch fabric is present. In this mode, classic line cards will transmit both the header and the data portion of the packet over the DBus. CEF256 and CEF720 line cards will only transmit headers over the DBus and transmit the data portion of the packet over the crossbar switch fabric.
Truncated mode results in centralized forwarding rates up to 15Mpps. In Truncated Mode, since the CEF256 and CEF720 line cards use the crossbar switch fabric to transmit data, overall aggregate bandwidth can actually be higher than the 32-Gbps shared bus capacity.
Performance of DFC enabled line cards are not affected by truncated mode and performance remains the same regardless of the line-card mix in the chassis.

Full link -


Jon

paul amaral Wed, 09/08/2010 - 09:34

I guess I trying to understand where the performance is impacted, I'm assuming its at the shared Dbus

level when using Classic and SFM together?

Also I'm trying to figure out why when I have an old flexwan card on slot 8 i see the sup720 in flow through (Bus) switching mode instead of truncated?

with the felxwan

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

Switch Fabric Resources

  Bus utilization: current: 0%, peak was 14% at 22:13:21 edt Sat Apr 4 2009

  Fabric utilization:     Ingress                    Egress

    Module  Chanl  Speed  rate  peak                 rate  peak

    1       0         8G    0%    0%                   0%    0%

   2       0         8G    0%    0%                   0%    0%

    5       0        20G    0%    0%                   0%    0%

    6       0         8G    0%    0%                   0%    0%

  Switching mode: Module                                        Switching mode

                  1                                                  truncated

                  2                                                  truncated

                  5                                               flow through

                  6                                                  truncated

without the flexwan:

Fabric module is not  required for system to operate
Modules are allowed to operate in bus mode
Truncated mode is allowed, due to presence of Standby supervisor module

Module Slot     Switching Mode
    1                 Crossbar
    2                 Crossbar
    5                     dCEF
    6                 Crossbar

thanks Paul

Jon Marshall Wed, 09/08/2010 - 12:03

Paul

I guess I trying to understand where the performance is impacted, I'm assuming its at the shared Dbus

level when using Classic and SFM together?

Exactly. As the bit i cut and paste says -

1) compact = header over sent over DBus

2) truncated = header + data sent over DBus

hence the reason Cisco can never give exact figures on truncated forwarding because the data portion of the packet varies.

Jon

paul amaral Wed, 09/08/2010 - 12:52

Jon,

that's what I figured but im glad you got rid of my doubt.

thanks, Paul.

Actions

This Discussion