Server protocol:Changes

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Below we outline the changes in the server-to-server (S2S) protocol between UnrealIRCd 3.2.x and UnrealIRCd 4.

Note that all traffic we discuss here is server-to-server traffic. At no point we expose such traffic to regular clients (eg: the use of UID's).

Removed features

The following features were removed in UnrealIRCd 4

SJB64 (Base64 timestamps)

This feature was removed because it only saves a few bytes of bandwidth per line at a cost of complicating the code too much.

ZIP (Zip links)

This feature was removed when the I/O engine was rewritten. It may or may not be re-introduced at a later point.

NS (Server numerics)

Server numerics have been removed but have been replaced by SID's (see next section)

New features

These are new features that you can choose to enable (or not).

SID (Server and nick id's)


Server id's (SID's) work very similar to the removed server numerics feature and consist of 3 alphanumerical characters which uniquely identify a server (where the first character is always a digit). No base64 encoding involved. You can (theoretically) use a SID anywhere a server name is used, like: NOTICE #chan :Hello

Can become:

:001 NOTICE #chan :Hello

SID command

When a server links in you now receive a "SID" rather than a "SERVER" command. Refer to the Server ID page for more information.


When you enabvle SID you also get user id's (UID's). UID's consist of alphanumerical characters and can (theoretically) be used at any place where you use a nick name. The first 3 characters identify the SID of the server where the user is on (this is part of the UID) and thus a UID will always start with a digit.

The benefit of using UID's is that it really uniquely identifies a user regardless of the current nick name. This allows us to solve some long-standing problems where nick collisions and race conditions cause desynchs such as 'ghosts' in a channel.


:One NOTICE Two :Hi there

Can become:


As you can see, it doesn't necessarily shorten the length. That isn't the purpose of UID. The benefit of UID is the uniqueness described earlier.

UID command

Instead of "NICK" protocol messages you will receive "UID". See also:


If you want to support SID's and UID's then we suggest:

  • store the SID & UID in your server & client structs
  • make functions like find_person() also search this field. UID's and SID's just look like regular names after all, except they start with a digit
  • ensure you handle the SID and UID commands
  • send SID in PROTOCTL to indicate your software supports SID & UID