A = 10.0.0.0/8
B = 172.16.0.0/16
C = 192.168.1.0/24
############################################################
0 = 00000000
126 = 01111110
The first bit match
ip prefix-list Incoming seq 5 deny 0.0.0.0/1 ge 8 le 8
############################################################
128 = 10000000
191 = 10111111
The first 2 bits match
ip prefix-list Incoming seq 5 deny 128.0.0.0/2 ge 16 le 16
############################################################
192 = 11000000
223 = 11011111
The first 3 bits match
ip prefix-list Incoing seq 5 deny 192.0.0.0/3 ge 24 le 24
###########################################################
10.0.0.0-10.255.255.255
00001010.00000000.00000000.00000000 = 10.0.0.0 = 10.0.0.0/8
00001010.11111111.11111111.11111111 = 10.255.255.255
172.16.0.0-172.31.255.255
10101100.00010000.00000000.00000000 = 172.16.255.255 = 172.16.0.0/12
10101100.00011111.11111111.11111111 = 172.31.255.255
192.168.0.0-192.168.255.255
11000000.10101000.00000000.00000000 = 192.168.0.0 = 192.168.0.0/16
11000000.10101000.11111111.11111111 = 192.168.255.255
193.0.0.0 – 193.255.255.255 =
11000001.00000000.00000000.00000000 = 193.0.0.0
11000001.11111111.11111111.11111111 = 193.255.255.255
128.0.0.0 – 191.255.255.255 =
10000000.00000000.00000000.00000000
10111111.11111111.11111111.11111111
0.0.0.0 – 63.255.255.255
00000000.00000000.00000000.00000000
00111111.11111111.11111111.11111111
****************************************************************************************************************
• In address range 193.0.0.0 – 193.255.255.255, do not accept prefixes with subnet masks longer than /20.
• In address range 128.0.0.0 – 191.255.255.255, do not accept prefixes with subnet masks longer than /18.
• In address range 0.0.0.0 – 63.255.255.255, do not accept prefixes with subnet masks longer than /12.
• Never accept prefixes longer than /24.
***************************************************************************************************************
ip prefix-list Incoming seq 5 deny 10.0.0.0/8 le 32
ip prefix-list Incoming seq 10 deny 172.16.0.0/12 le 32
ip prefix-list Incoming seq 15 deny 192.168.0.0/16 le 32
ip prefix-list Incoming seq 20 deny 193.0.0.0/8 ge 21
ip prefix-list Incoming seq 25 deny 128.0.0.0/2 ge 19
ip prefix-list Incoming seq 30 deny 0.0.0.0/2 ge 13
ip prefix-list Incoming seq 35 permit 0.0.0.0/0 le 24
