default or selected kernelversion does not have config value CONFIG_E2100.
Result is shown for kernelversion 6.2.5

Cabletron E21xx support

modulename: e2100.ko

configname: CONFIG_E2100

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet (10 or 100Mbit)
└─>Cabletron E21xx support
In linux kernel since version 2.6.12  
If you have a network (Ethernet) card of this type, say Y and read
the Ethernet-HOWTO, available from

To compile this driver as a module, choose M here. The module
will be called e2100.

source code: