How to remove IP(s) from a text file based on given CIDR?

EDIT: Since OP added few more samples to handle lines with / present one could try following.

awk -F'/' -v val="1.1.1.0/24" '
BEGIN{
  match(val,/.*\./)
  matched=substr(val,RSTART,RLENGTH-1)
  split(substr(val,RSTART+RLENGTH),arr,"/")
  for(i=arr[1];i<=arr[2];i++){
   skip[matched"."i]
  }
}
!($1 in skip)
'  Input_file

Could you please try following, written and tested with shown samples in GNU awk. Where variable val is your range of IPs.

awk -v val="1.1.1.0/24" '
BEGIN{
  match(val,/.*\./)
  matched=substr(val,RSTART,RLENGTH-1)
  split(substr(val,RSTART+RLENGTH),arr,"/")
  for(i=arr[1];i<=arr[2];i++){
   skip[matched"."i]
  }
}
!($0 in skip)
'  Input_file

Explanation: Adding detailed explanation for above.

awk -v val="1.1.1.0/24" '                        ##Starting awk program from here and creating variable val which has that range here.
BEGIN{                                           ##Starting BEGIN section of this program from here.
  match(val,/.*\./)                              ##using match function to match everything till . in variable val here.
  matched=substr(val,RSTART,RLENGTH-1)           ##Creating matched which has sub string of matched regex value in var variable.
  split(substr(val,RSTART+RLENGTH),arr,"/")      ##Splitting rest of value of var which is actual range into array arr here.
  for(i=arr[1];i<=arr[2];i++){                   ##Running for loop from 1st item value to 2nd item value of array here.
   skip[matched"."i]                             ##Creating skip array which has index as matched(variable) dot and i here, it contains which ips to be negleted basically.
  }
}
!($0 in skip)                                    ##In main block of program checking condition if current line is NOT present in skip then print that line.
' Input_file                                     ##Mentioning Input_file name here.