EventIds are application specific so you can use whatever ranges you like. Just ensure you document what you have used and where so that you can ensure you don t use an id twice, or to facilitate easier debugging.

But keep in mind...

Like when Henry Ford said "you can have any color you want as long as it s black" - you can also use whatever range you like as long as that range falls inside the range of 0 and 65535.

Sure enough, it is up to the author to define and track event IDs they use and what they mean.

Here is a reference: http://msdn.microsoft.com/en-us/library/e29k5ebc.aspx - Particularly interesting is the part about not writing messages with IPv6 addresses (because of the % character) to the event log. I bet you can use a parameter to work around that though.

The hi bits of the ID are reserved for testing, debug and other flags used for development. The usable bits are:

0x0000 - 0xffff

See: Event Message Structure

The upper bits should be avoided but all values for the bottom bits are available if you create a custom source. If you use a system or pre-existing source you will collide and likely get the wrong message. Messages are taken from the registered sources message DLL file. A custom message file can be built using the message file compiler from the SDK.

Edit1: I tested that and it is not true that eventID is 32bits. It is only 16 bits.

eventId is Int32, from -2,147,483,648 to 2,147,483,647

EventLog.WriteEntry Method (String, String, EventLogEntryType, Int32)

public static void WriteEntry(
    string source,
    string message,
    EventLogEntryType type,
    int eventID
)

Technically you can use any values between 1 - 65536 for that.

But if you are someone who writes tons of verbose log like me you will find it difficult to relate a bunch of entries together then I would suggest to generate a random unique value every time the code executes with this you can identify the events, even the much better idea would be to create your own log & source to use this instead of writing everything in the Application log. like

 Random rnd = new Random();
 EventId = rnd.Next(0, 65535);