diff --git a/excel/network_ip_masks b/excel/network_ip_masks
new file mode 100644
index 0000000..3ddfd49
--- /dev/null
+++ b/excel/network_ip_masks
@@ -0,0 +1,114 @@
+A1 = IP address
+B1 = CIDR netmask
+
+ref https://gist.github.com/f-steff/d2ef30bed5328f0e417d635d3b46e256
+
+
+Calculate netmask:
+==================
+
+=bin2dec(mid(REPT("1",B1)&rept("0",32-B1),1,8))&"."&
+bin2dec(mid(REPT("1",B1)&rept("0",32-B1),9,8))&"."&
+bin2dec(mid(REPT("1",B1)&rept("0",32-B1),17,8))&"."&
+bin2dec(mid(REPT("1",B1)&rept("0",32-B1),25,8))
+
+
+Calculate start of IP range:
+============================
+
+=BITAND( 
+  (LEFT(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),0))-1))
+  ,
+  (bin2dec(mid(REPT("1",B1)&rept("0",32-B1),1,8))) 
+)
+&"."&
+BITAND( 
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),1))+1,find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))-find(char(160),SUBSTITUTE(C1,".",CHAR(160),1))))
+  ,
+  (bin2dec(mid(REPT("1",B1)&rept("0",32-B1),9,8)) )
+)
+&"."&
+BITAND(
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))+1,find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))-find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))))
+  ,
+  (bin2dec(mid(REPT("1",B1)&rept("0",32-B1),17,8)))
+)
+&"."&
+BITAND(
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))+1,find(char(160),SUBSTITUTE(A1&".",".",CHAR(160),4))-find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))-1))
+  ,
+  bin2dec(mid(REPT("1",B1)&rept("0",32-B1),25,8))
+)
+
+
+Calculate end of IP range:
+==========================
+
+=BITOR( 
+  (LEFT(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),0))-1))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),1,8))) 
+)
+&"."&
+BITOR( 
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),1))+1,find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))-find(char(160),SUBSTITUTE(C1,".",CHAR(160),1))))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),9,8)) )
+)
+&"."&
+BITOR(
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))+1,find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))-find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),17,8)))
+)
+&"."&
+BITOR(
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))+1,find(char(160),SUBSTITUTE(A1&".",".",CHAR(160),4))-find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),25,8)))
+)-1
+
+
+Calculate Broadcast IP:
+=======================
+
+=BITOR( 
+  (LEFT(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),0))-1))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),1,8))) 
+)
+&"."&
+BITOR( 
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),1))+1,find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))-find(char(160),SUBSTITUTE(C1,".",CHAR(160),1))))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),9,8)) )
+)
+&"."&
+BITOR(
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))+1,find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))-find(char(160),SUBSTITUTE(A1,".",CHAR(160),2))))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),17,8)))
+)
+&"."&
+BITOR(
+  (MID(A1, find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))+1,find(char(160),SUBSTITUTE(A1&".",".",CHAR(160),4))-find(char(160),SUBSTITUTE(A1,".",CHAR(160),3))))
+  ,
+  (255-bin2dec(mid(REPT("1",B1)&rept("0",32-B1),25,8)))
+)
+
+
+Calculate number of hosts:
+==========================
+
+=2^(32-B1)-1
+
+
+===================================================================================================================================
+(Does not follow on from above columns.)
+===================================================================================================================================
+
+Convert traditional netmask in A1 to CIDR:
+
+="/"&32-LEN(SUBSTITUTE(TEXT(DEA1BIN(MID(A1,1,FIND(".",A1)-1)),"00000000")&TEXT(DEA1BIN(MID(A1,1+FIND(".",A1),FIND(".",A1,FIND(".",A1)+1)-FIND(".",A1)-1)),"00000000")&TEXT(DEA1BIN(MID(A1,1+FIND(".",A1,FIND(".",A1)+1),FIND(".",A1,FIND(".",A1,FIND(".",A1)+1)+1)-FIND(".",A1,FIND(".",A1)+1)-1)),"00000000")&TEXT(DEA1BIN(RIGHT(A1,LEN(A1)-FIND(".",A1,FIND(".",A1,FIND(".",A1)+1)+1))),"00000000"),"1",""))
+
+(ref https://www.reddit.com/r/excel/comments/9ivaal/simple_formula_ip_subnet_masks_to_cidr/)