FIX Difference between Security Definition Request (MsgType=c) and Security List Request (MsgType=x)

Question

In FIX what is the difference between Security Definition Request (MsgType=c) and Security List Request (MsgType=x)

Answer 1

The documentation says the following:

The Security List Request message is used to return a list of securities from the counterparty that match criteria provided on the request

and

The Security Definition Request message is used for the following:

1. Request a specific Security to be traded with the second party. The request security can be defined as a multileg security made up of one or more instrument legs.

2. Request a set of individual securities for a single market segment.

3. Request all securities, independent of market segment.

It appears there is some overlap between the two message types' stated intents.

Given the general fudginess of real-world applications of FIX protocol, your best practice is to check the documentation of your intended counterparty. Odds are, they have very specific ways of using each message type, and it's possible they may not even support both.

If you are designing your own FIX interface, then you have the flexibility to use either or both of these messages as you see fit. You don't have to support both of them.