In all Execution Report messages, the FIX Server populates the trading system’s unique order identifier in OrderID(37). OrderID(37) is unique during the session and among all active GTC/GTD orders. It shall not change with modifications/cancellations of the order.

In HM mode, the Fix Client shall echo tag 37 back in Order Cancel and Cancel/Replace Requests. In other modes, the Fix Client can optionally echo tag 37 back in Order Cancel and Cancel/Replace Requests. Also in NE mode FIX Client may optionally use tag 37 as the only field for referencing the order in an Order Cancel and Cancel/Replace Requests (required for enabling External Orders Support functionality described in section 3.7).

All application messages sent by FIX Client are checked for duplicate ClOrdID(11).

The uniqueness of ClOrdID(11) identifier must be maintained during FIX session. If orders with duration of more than one FIX session are used, FIX Client needs to cater for uniqueness across those.  If two new orders are sent with the same ClOrdID(11), the second one is rejected. ClOrdID(11) is generated in the following way:

•    In NE mode, the maximum length is 14 or 16 (depends on how FIX Server is configured) and has the following format: YYMMDDID (where ID is unique identifier).­

•    In DW mode, the maximum length is 16 and has the following format: YYMMDDID (where ID is unique identifier).

•    In HM mode, the length is 10 (unique identifier padded with “0”s from left).

•    In HS and GD mode, the maximum length is 10 (unique identifier).