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CoS or DSCP based QoS Policies

I have to configure QoS on a VSS with the following modules installed:

Switch Number:     1   Role:   Virtual Switch Active
----------------------  -----------------------------
Mod Ports Card Type                              Model              Serial No.
--- ----- -------------------------------------- ------------------ -----------
  1   48  CEF720 48 port 1000mb SFP              WS-X6848-SFP       SAL16042610
  3   48  CEF720 48 port 10/100/1000mb Ethernet  WS-X6848-GE-TX     SAL16095Y48
  4   48  CEF720 48 port 10/100/1000mb Ethernet  WS-X6848-GE-TX     SAL16095Y3F
  5    5  Supervisor Engine 2T 10GE w/ CTS (Acti VS-SUP2T-10G       SAL1543TRQ9
  9    8  DCEF2T 8 port 10GE                     WS-X6908-10G       SAL1539QYTC

Mod MAC addresses                       Hw    Fw           Sw           Status
--- ---------------------------------- ------ ------------ ------------ -------
  1  c464.1341.7a50 to c464.1341.7a7f   1.0   12.2(18r)S1  15.0(1)SY4   Ok
  3  0007.7df7.4618 to 0007.7df7.4647   1.0   12.2(18r)S1  15.0(1)SY4   Ok
  4  442b.0311.4a58 to 442b.0311.4a87   1.0   12.2(18r)S1  15.0(1)SY4   Ok
  5  7081.0583.88e8 to 7081.0583.88ef   1.1   12.2(50r)SYS 15.0(1)SY4   Ok
  9  0007.7d90.a1a0 to 0007.7d90.a1a7   1.1   12.2(50r)SYL 15.0(1)SY4   Ok

Mod  Sub-Module                  Model              Serial       Hw     Status
---- --------------------------- ------------------ ----------- ------- -------
  1  Distributed Forwarding Card WS-F6K-DFC4-A      SAL16085BLE  1.2    Ok
  3  Distributed Forwarding Card WS-F6K-DFC4-A      SAL16085BLL  1.2    Ok
  4  Distributed Forwarding Card WS-F6K-DFC4-A      SAL16095GH7  1.2    Ok
  5  Policy Feature Card 4       VS-F6K-PFC4        SAL1544UAL2  1.1    Ok
  5  CPU Daughterboard           VS-F6K-MSFC5       SAL1544UB95  1.1    Ok
  9  Distributed Forwarding Card WS-F6K-DFC4-E      SAL1529K4QC  1.0    Ok

On Cat6500 with SUP 2T and PFC4 QoS is enabled by default.

DSCP is trusted and preserved by default, independent of port state.

CoS is preserved by default for Layer 2 packets by default, independent of port state.

Additional Info about the queuing on the modules installed:

SUP 2T 10G - with Gigabit Ethernet Ports enabled it works CoS-based, with this interfaces disabled it works DSCP-based.

WS-X6848-GE-TX an WS-X6848-SFB works CoS-based, does not support DSCP-based queuing.

WS-X6908-10G - supports DSCP-based queuing

The options now are:

1) All policies CoS-based although the WS-X6980-10G supports DSCP-based queuing.

2) Policies for SUP and WS-X6848 CoS-based and the policies for the WS-X6908 DSCP-based

3) Disable Gigabit Ethernet Interfaces on the SUP hence it supports DSCP-based queuing policies, also use DSCP-based policies for the WS-X6908 and use CoS-based queuing policies for the WS-X6848.

The recommendation in the core is to use DSCP-based QoS.

The question is what to do?

Option 1) Less complexity and simpler configuration if only CoS-based policies are used.

Option 2) Least configuration necessary, mixture of CoS and DSCP-based policies

Option 3) Gigabit Ethernet ports on SUP have to be disabled, uses then DSCP-based queuing on all supported modules and CoS-based policies on all other modules.

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