Hobbit's subnet-boundary, size and mask poopsheet: rev of 001212 mask bits ibits imask ----- sizes ------------------ net-chunks... 0 0000 0000 1111 1111 255 /08, /16, /24 : one net of 256 0-255 128 1000 0000 0111 1111 127 /09, /17, /25 : 2 nets of 128 0-127, 128-255 192 1100 0000 0011 1111 63 /10, /18, /26 : 4 nets of 64 0-63, 64-127, 128-191, 192-255 224 1110 0000 0001 1111 31 /11, /19, /27 : 8 nets of 32 0-31, 32-63, 64-95, 96-127, 128-159, 160-191, 192-223, 224-255 240 1111 0000 0000 1111 15 /12, /20, /28 : 16 nets of 16 0-15, 16-31, 32-47, 48-63, 64-79, 80-95, 96-111, 112-127 128-143, 144-159, 160-175, 176-191, 192-207, 208-223, 224-239, 240-255 248 1111 1000 0000 0111 7 /13, /21, /29 : 32 nets of 8 0-7, 8-15, 16-23, 24-31, 32-39, 40-47, 48-55, 56-63 64-71, 72-79, 80-87, 88-95, 96-103, 104-111, 112-119, 120-127 128-135, 136-143, 144-151, 152-159, 160-167, 168-175, 176-183, 184-191 192-199, 200-207, 208-215, 216-223, 224-231, 232-239, 240-247, 248-255 252 1111 1100 0000 0011 3 /14, /22, /30 : 64 nets of 4 ; you figure it out: take each /29 range and cut it in half. ; each /30 has two hosts, a "zero" bcast, and a "ones" bcast. 254 1111 1110 0000 0001 1 /15, /23, /31 : 128 nets of 2 ; normally doesn't work for IP; may work for some aggregates or p-t-p links net & broadcast is low & high addr of each block quickie "dc" method for generating net boundaries: [ dla+ ] sb d sa lbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbxlbx ... f 16 o f ;; to print in hex RFC1219-style binary-sprinkling subnet assignment order, if on byte-boundaries Read *across*, not down, and cross out subnets as they get allocated. If someone takes a huge block, cross out all those contained inside it. 000 128 064 192 032 160 096 224 016 144 080 208 048 176 112 240 008 136 072 200 040 168 104 232 024 152 088 216 056 184 120 248 004 132 068 196 036 164 100 228 020 148 084 212 052 180 116 244 012 140 076 204 044 172 108 236 028 156 092 220 060 188 124 252 002 130 066 194 034 162 098 226 018 146 082 210 050 178 114 242 010 138 074 202 042 170 106 234 026 154 090 218 058 186 122 250 006 134 070 198 038 166 102 230 022 150 086 214 054 182 118 246 014 142 078 206 046 174 110 238 030 158 094 222 062 190 126 254 001 129 065 193 033 161 097 225 017 145 081 209 049 177 113 241 009 137 073 201 041 169 105 233 025 153 089 217 057 185 121 249 005 133 069 197 037 165 101 229 021 149 085 213 053 181 117 245 013 141 077 205 045 173 109 237 029 157 093 221 061 189 125 253 003 131 067 195 035 163 099 227 019 147 083 211 051 179 115 243 011 139 075 203 043 171 107 235 027 155 091 219 059 187 123 251 007 135 071 199 039 167 103 231 023 151 087 215 055 183 119 247 015 143 079 207 047 175 111 239 031 159 095 223 063 191 127 255