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5406zl QoS behavior - overwrite DSCP value for VLAN

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  • 1.  5406zl QoS behavior - overwrite DSCP value for VLAN

    Posted 13 days ago
    Using an older 5406zl (FW K.15.18.0015), I'm seeing QoS behavior that I don't believe is correct. This is a fairly simple setup - a Polycom VoIP phone connected to the 5406zl switch and the switch connected to the edge router.


    Ports D14, B19 on the switch are assigned to VLAN 10, along with the VVX311 and eth4 on the firewall.

    The intent is to have the switch assign a DSCP to all traffic on VLAN 10, overwriting the DSCP value from the VVX311 config. For testing I set the VVX311 to a DSCP value of 26 (AF31) and a 802.1Q value of 3.


    On the switch, type-of-service is set to Differentiated Services
    HP-5406zl# show qos type-of-service
    DSCP-based Prioritization : Differentiated Services
    and vlan-priority is configured (no other classifiers are configured)
    HP-5406zl# show qos vlan-priority

    VLAN-based Prioritization

    VLAN ID Apply rule | DSCP Priority
    ------- ----------- + ------ -----------
    1 No-override | No-override
    2 No-override | No-override
    3 No-override | No-override
    10 DSCP | 101110 5

    With the configuration I would expect all traffic leaving port B19 on the switch to have a DSCP value of 46 and 802.1Q priority set to 5. When I do a packet capture on eth4 on the firewall however, the DSCP value is unchanged from what is set on the phone. Also, the 802.1Q PRI value is changed to 4.


    For comparison here's a capture directly from the phone eth0 interface before the packet gets to the switch:


    As you can see the DSCP is not changed by the switch but the PRI field is. According the Advanced Traffic Management Guide for this switch, the DSCP value should be overwritten.


    Is this an issue of me lacking understanding of how this should work or is there a technical problem here?

    ------------------------------
    Chris McFarling
    ------------------------------


  • 2.  RE: 5406zl QoS behavior - overwrite DSCP value for VLAN
    Best Answer

    Posted 13 days ago
    *Resolved*

    It was my misunderstanding of the type-of-service classifier. Having type-of-service enabled and set to Differentiated Services causes the switch to remark packets based on the following table
    HP-5406zl# show qos type-of-service
    DSCP-based Prioritization : Differentiated Services


    Codepoint DSCP Policy | Priority
    --------- ----------- + -----------
    000000 | 0
    000001 | No-override
    000010 | No-override
    000011 | No-override
    000100 | No-override
    000101 | No-override
    000110 | No-override
    000111 | No-override
    001000 | 1
    001001 | No-override
    001010 | 1
    001011 | No-override
    001100 | 1
    001101 | No-override
    001110 | 2
    001111 | No-override
    010000 | 2
    010001 | No-override
    010010 | 0
    010011 | No-override
    010100 | 0
    010101 | No-override
    010110 | 3
    010111 | No-override
    011000 | 3
    011001 | No-override
    011010 | 4
    011011 | No-override
    011100 | 4
    011101 | No-override
    011110 | 5
    011111 | No-override
    100000 | 4
    100001 | No-override
    100010 | 6
    100011 | No-override
    100100 | 6
    100101 | No-override
    100110 | 7
    100111 | No-override
    101000 | 5
    101001 | No-override
    101010 | No-override
    101011 | No-override
    101100 | No-override
    101101 | No-override
    101110 | 5
    101111 | No-override
    110000 | 6
    110001 | No-override
    110010 | No-override
    110011 | No-override
    110100 | No-override
    110101 | No-override
    110110 | No-override
    110111 | No-override
    111000 | 7
    111001 | No-override
    111010 | No-override
    111011 | No-override
    111100 | No-override
    111101 | No-override
    111110 | No-override
    111111 | No-override

    And since the type-of-service classifier has a higher precedence than vlan-priority, the vlan-priority was being ignored. The resolution was to disable type-of-service.

    ------------------------------
    Chris McFarling
    ------------------------------