I posted Python find first network hop about trying to find the first hop and the more I thought about it, the easier it seemed like it would be a process the routing table in python. I'm not a programmer, I don't know what I'm doing. :p

This is what I came up with, the first issue I noticed is the loopback interface doesn't show up in the /proc/net/route file- so evaluating 127.0.0.0/8 will give you the default route... for my application, that doesn't matter.

Anything else major I'm overlooking? Is parsing ip route get <ip> still a better idea?

import re
import struct
import socket'''Read all the routes into a list. Most specific first.# eth0  000219AC        04001EAC        0003    0       0       0       00FFFFFF ...
'''
def _RtTable():_rt = []rt_m = re.compile('^[a-z0-9]*\W([0-9A-F]{8})\W([0-9A-F]{8})[\W0-9]*([0-9A-F]{8})')rt = open('/proc/net/route', 'r')for line in rt.read().split('\n'):if rt_m.match(line):_rt.append(rt_m.findall(line)[0])rt.close()return _rt'''Create a temp ip (tip) that is the entered ip with the host section striped off.  Matching to routers in order, the first match should be the most specific.If we get 0.0.0.0 as the next hop, the network is likely(?) directly attached- the entered IP is the next (only) hop
'''
def FindGw(ip):int_ip = struct.unpack("I", socket.inet_aton(ip))[0]for entry in _RtTable():tip = int_ip & int(entry[2], 16)if tip == int(entry[0], 16):gw_s = socket.inet_ntoa(struct.pack("I", int(entry[1], 16)))if gw_s == '0.0.0.0':return ipelse:return gw_sif __name__ == '__main__':import sysprint FindGw(sys.argv[1])

In the man page of proc file system it is given that.

   /proc/netvarious net pseudo-files, all of which give the status of some part ofthe networking layer.  These files contain ASCII structures and  are,there‐fore, readable with cat(1).However, the standard netstat(8) suite provides much cleaner access to these files.

Just rely on the tools designed for those purposes. Use netstat, traceroute or any other standard tool. Wrap those commands cleanly using subprocess module and get the information for what you are looking for.