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08.05.2008 at 02:36PM PDT, ID: 23623959
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9.1

how to do IP prefix matching efficiently in Python?

Asked by summer_soccer in Python Scripting Language

Tags:

I asked a similar question previously, and got some answers from Mish. I got to implement code as suggested in the link Mish provided, but I found it is very inefficient. My code is attached.

The basic idea is, first I read in all prefixes into a list. There are about 300k such prefixes. Then for each IP address, I need to do a sequential comparison with all such 300k prefixes to find a match. This can take a long time. Further, because I want the longest matching prefix, I cannot stop in the middle when a match is found, because it might not be the longest matching prefix.

I have found an package pysubnettree-0.11 on the Internet, but it requires root privilege to get installed. My code will run on multiple hosts without root privilege.

Does anybody have any ideas how to resolve this problem? Many thanks!Start Free Trial 
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# convert an IP address from its dotted-quad format to its 
    # 32 binary digit representation 
    def ip2bin(self, ip): 
        b = "" 
        inQuads = ip.split(".")
        outQuads = 4
        for q in inQuads:
            if q != "":
                b += self.dec2bin(int(q),8)
                outQuads -= 1
        while outQuads > 0:
            b += "00000000"
            outQuads -= 1
        return b
 
    # convert a decimal number to binary representation
    # if d is specified, left-pad the binary number with 0s to that length
    def dec2bin(self, n,d=None):
        s = ""
        while n>0:
            if n&1:
                s = "1"+s
            else:
                s = "0"+s
            n >>= 1
        if d is not None:
            while len(s)<d:
                s = "0"+s
        if s == "": s = "0"
        return s
 
    def match_ip_prefix(self, ip, prefix):
        #print 'the prefix is ', prefix
        #print 'the ip is ', ip
        parts = prefix.split("/")
        baseIP = self.ip2bin(parts[0])
        subnet = int(parts[1])
        # Python string-slicing weirdness:
        # "myString"[:-1] -> "myStrin" but "myString"[:0] -> "" 
        
        if subnet == 32: 
            if self.ip2bin(ip) == baseIP:
                return True
            else:
                return False
 
        # for any other size subnet, print a list of IP addresses by concatenating 
        # the prefix with each of the suffixes in the subnet 
        else: 
            ipPrefix = baseIP[:-(32-subnet)] 
            ipinbin = self.ip2bin(ip) 
            partip = ipinbin[:-(32-subnet)] 
            
            #print 'partIP is ', partip, 'ipPrefix is ', ipPrefix 
            
            if ipPrefix == partip: 
                #print 'they match' 
                return True 
            else: 
                #print 'they do not match' 
                return False
[+][-]08.07.2008 at 03:44AM PDT, ID: 22179584

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[+][-]08.07.2008 at 02:32PM PDT, ID: 22185647

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[+][-]08.07.2008 at 06:21PM PDT, ID: 22186872

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[+][-]08.07.2008 at 06:25PM PDT, ID: 22186888

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[+][-]08.08.2008 at 07:40AM PDT, ID: 22190296

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About this solution

Zone: Python Scripting Language
Tags: python
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Solution Provided By: ramrom
Participating Experts: 1
Solution Grade: A
 
 
 
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