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How to dissect packets whose destination IP lies within a range of IP addresses

asked 2019-01-07 16:37:41 +0000

JCAMP gravatar image

updated 2019-01-08 12:15:12 +0000

I'm trying to only dissect packets whose destination address is within a range of IP addresses. E.g. all packets between 130.0.0.1 and 130.255.255.255. How do I take the destination IP address from the packet and compare it to the upper and lower bound of the IP addresses to be dissected?

As a prototype I've tried making a variable of type address and setting the values to what I think they should be. So type AT_IPv4, len = 4, and data pointing to an array that is 4 bytes long, with those being set to that of the destination ip address of the packets. But when I use cmp_address(&pinfo->dst, &ip)==1 it comes out as false, have tried using net_dst instead of dst and I get the same result.

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answered 2019-01-07 20:14:36 +0000

cmaynard gravatar image

Are you sure you're using cmp_address() correctly? Like memcmp(), it returns 0 for a match.

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My mistake, I am now

JCAMP gravatar imageJCAMP ( 2019-01-08 10:43:18 +0000 )edit

So the prototype of using IPs that are equals works. But how do I compare against an upper and lower bound of IPs that the dissector would accept? So if the destination is between 130.0.0.1 and 130.255.255.255 then do some stuff.

JCAMP gravatar imageJCAMP ( 2019-01-08 10:57:53 +0000 )edit

As documented in address.h, cmp_address(addr1, addr2) returns 0 if they're equal, a positive number if addr1 > addr2 and a negative number if addr1 < addr2. So you can do something like:

if ((cmp_address(&pinfo->dst, &ip_lower) >= 0) && (cmp_address(&pinfo->dst, &ip_upper) <= 0)) {
    /* Accept the packet and process it */
} else {
    /* Reject the packet */
}
cmaynard gravatar imagecmaynard ( 2019-01-08 13:53:11 +0000 )edit

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Asked: 2019-01-07 16:37:41 +0000

Seen: 78 times

Last updated: Jan 08