Conversion from IP Range to CIDR Mask

问题

I've been working on an algorithm for converting an IP Range to a list IPs in CIDR Notation (will be mentioned as tuples henceforth). Now, what puzzles me is figuring out what is the Worst Case Scenario for this conversion;

What is the maximum number of tuples I can get for an IPv4 Range? What is the maximum number of tuples I can get for an IPv6 Range? How was this calculated?erp

I'm using a modified C version (which is not recursive) of the following Python script:

 1 #!/usr/bin/env python
 2 
 3 import sys
 4 import re
 5 
 6 def ip2int(ip) :
 7         ret = 0
 8         match = re.match("(\d*)\.(\d*)\.(\d*)\.(\d*)", ip)
 9         if not match : return 0
10         for i in xrange(4) : ret = (ret << 8) + int(match.groups()[i])
11         return ret
12 
13 def int2ip(ipnum) :
14         ip1 = ipnum >> 24
15         ip2 = ipnum >> 16 & 0xFF
16         ip3 = ipnum >> 8 & 0xFF
17         ip4 = ipnum & 0xFF
18         return "%d.%d.%d.%d" % (ip1, ip2, ip3, ip4)
19 
20 def printrange(startip, endip) :
21         bits = 1
22         mask = 1
23         while bits < 32 :
24                 newip = startip | mask
25                 if (newip>endip) or (((startip>>bits) << bits) != startip) :
26                         bits = bits - 1
27                         mask = mask >> 1
28                         break
29                 bits = bits + 1
30                 mask = (mask<<1) + 1
31         newip = startip | mask
32         bits = 32 - bits
33         print "%s/%d" % (int2ip(startip), bits)
34         if newip < endip : 
35                 printrange(newip + 1, endip)
36 
37 while 1 :
38         line = sys.stdin.readline().strip()
39         if not line : break
40         chars = line.split(" ")
41         print "#%s - %s" % (chars[0], chars[1])
42         ip1 = ip2int(chars[0])
43         ip2 = ip2int(chars[1])
44         printrange(ip1, ip2)

回答1:

It is just guess, but seems to be, that maximum number for CIDR prefixes in single IPv4 range is 62 (32*2 - 2), and for IPv6 - 254 (128*2 - 2).

来源：https://stackoverflow.com/questions/10228219/conversion-from-ip-range-to-cidr-mask

标签

math

cidr