HowTo Map TCP/UDP port to priority via LLDP DCBX TLV on MLNX-OS (ISCSI example)

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    Mapping priority automatically for applications that use TCP/UDP transport methods could be useful. This is important for example, for lossless applications such as ISCSI, when lossless network is required and achieved via PFC.

    In this post, we will show an example to configure the switch to send LLDP DCBX TLV with Application Priority that maps ISCSI TCP port 3260 to priority 3.

    The server should run lldptool or other application that will perform this mapping and send the ISCSI traffic via priority 3 (as configured)

    This feature is available starting with MLNX-OS version 3.6.4006

     

    References

     

    Setup

    A simple setup with two servers connected to a Mellanox Switch.

     

    Configuration

     

    Switch Configuration

    1. Enable LLDP

    switch (config) # lldp

     

    2. Enable ISCSI application priority. This is enabled on TCP port 3260

    switch (config) # dcb application-priority tcp iscsi 3

     

    Note: that other application based on UDP or TCP could be set as well.

    For example:

    switch (config) # dcb application-priority tcp <any port> <any priority 0-7>

    switch (config) # dcb application-priority udp <any port> <any priority 0-7>

     

    Server Configuration

    The server should run lldptool or other application that will perform this mapping and send the ISCSI traffic via priority 3 (as configured).

    Wireshark output

    If you run wireshark on the server, you can capture those LLDP TLVs (see attached below).

    In this example, we can see the Application Priority TLV with port 0xcbc (3260) running over TCP.