hosts.allow not always working... misses some IPs

[Kerry B. Rogers]

>>Kerry B. Rogers wrote:
>>>>[...]
>>>>I think the netmask is wrong.  When you apply the third octet of the
>>>>netmask (251) to the IP address (220) the result will be 216, which is
>>>>then compared with 220.  Since the numbers differ the rule doesn't
>>>>apply, which is to be expected.
>>>>
>>>>Are you sure that the netmask's third octet shouldn't have been 254, 252
>>>>or 248 instead for proper masking, depending on the range of addresses
>>>>you'd like to cover?
>>> 
>>> Uwe... how did you come up with netmask 251 applied to 220 equals 216? I'm
>>> confused about how one
>>> would determine the proper netmask. I think my formula is wrong and would
>>> like to get it right. I'm trying to convert the ARIN data line:
>>> 
>>> arin|CA|ipv4|199.185.220.0|1280|19940222|assigned
>>> 
>>> to a hosts.allow line and come up with:
>>> 
>>> smtp : 199.185.220.0/255.255.251.0 : deny
>>> 
>>> using the formula:
>>> 
>>> MaskFromIPRange = DoubleToIPAddress(IPAddressToDouble("255.255.255.255") -
>>> (IPAddressToDouble(strLastIP) - IPAddressToDouble(strFirstIP)))
>>> 
>>> or, translated symbolically:
>>> 
>>> Mask = 255.255.255.255 - 199.185.224.255 - 199.185.220.0
>>> 
>>> which (mathematically) is:
>>> 
>>> Mask = 4294967295 - 3350847743 - 3350846464
>>> 
>>> I guess using 255.255.255.255 and subtracting the difference of the IP range
>>> is not the proper way to arrive at a netmask. What is? Anyone?
>>
>>Netmasks are supposed to be calculated bit-wise, not by subtraction, and 
>>they can cover only address ranges that are a power of two.  So you need 
>>two ranges in your case: the first 1024 addresses and the remaining 256 
>>(adds up to 1280).  In C syntax the formular for the netmask would be:
>>
>>   netmask = ^(number_of_addresses - 1);
>>
>>This results in
>>
>>   smtp : 199.185.220.0/255.255.252.0 199.185.224.0/255.255.255.0 : deny
>>
>>If you don't have a calculator with a binary mode you can easily do this 
>>bit by bit on a piece of paper.  First write down 1023 (1024 - 1) in 
>>binary form (all 32 bits representing an IPv4 address), then invert the 
>>bits, and finally convert them back into a decimal number.  Do the same 
>>for the second range (256 - 1), and adapt the base address for this 
>>range accordingly.
>>
>>Hope this explanation was clear enough.
>>
>>    Uwe

Uwe, thanks so very much for helping me out here. If I have you correct, then the following would be correct, right?:

arin|US|ipv4|24.30.0.0|24576|0|allocated

smtp : 24.30.0.0/255.255.192.0 24.30.64.0/255.255.224.0 : deny

Thanks,

Kerry