Allen-Bradley E Series Installation Instructions Manual page 11

Set the Module's Network Address Switches
Use your fingers or a small screwdriver to set the module's network address
switches. For modules in a standalone chassis, you must specify a unique
ControlNet network address; for modules in a redundant chassis, you must
specify the same address for the secondary module that you specified for the
corresponding primary module.
Side of Module
TIP
You can select an address of 01 to 99 for modules in a
standalone chassis or 01 to 98 for modules in redundant
chassis. 00 is an invalid ControlNet network address.
ControlLogix ControlNet Interface Module 11
Top of Module
This module's network
address is 23.
Publication
1756-IN604A-EN-P - February 2006