Date: Wed, 24 Jan 2007 11:23:19 -0600 (Central Standard Time) From: Mark Jacobson To: 810-023-01-spring@uni.edu Subject: Legal subnet mask values (besides 255 and 0) Hi 023 students, I didn't get time to show what 128, 192, 224, 240, 248, 252 and 254 had in common today in class. The following should make that clear. The bc program is the Unix and Linux basic calculator. - - math-cs:~> bc bc 1.06 Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc. obase=2 <------ make the output base be base two binary instead of the default base ten decimal. 128 10000000 192 This shows why 128 and 128 + 64 and 128 + 64 + 32 and 11000000 128 + 64 + 32 + 16 and 224 11100000 128 + 64 + 32 + 16 + 8 and 240 128+64+32+16+8+4 and 11110000 128+64+32+16+8+4+2 are legal subnet 248 mask values. 11111000 252 11111100 <--------- 128 + 64 + 32 + 16 + 8 + 4 = 252 UNI subnet mask used to be 255.255.252.0 254 11111110 255 11111111 We will have a hands-on class in Wright 112 on Friday. Reminder: We have quiz one on Monday (January 29th). Mark