troubleshooting Question

how to do IP prefix matching efficiently in Python?

Avatar of summer_soccer
summer_soccer asked on
Python
6 Comments1 Solution2808 ViewsLast Modified:
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!
# 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
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