Linux /Proc/Net/Route Addresses Unreadable

  • 9/4/2014
  • 2-minute read

So you may have looked at /proc/net/route before and thought how the heck am I suppose to read this. Well here is the low down.

This file uses endianness to store the addresses as hexadecimal, in reverse; for example 192 as hex is C0 :

In []: hex(192)
Out[]: '0xc0'

So lets take a look at our route file:

Iface   Destination     Gateway         Flags   RefCnt  Use     Metric  Mask            MTU     Window  IRTT
eth0    00087F0A        00000000        0001    0       0       0       00FFFFFF        0       0       0
eth0    0000FEA9        00000000        0001    0       0       1002    0000FFFF        0       0       0
eth0    00000000        01087F0A        0003    0       0       0       00000000        0       0       0

Now the first entry has a destination of 00087F0A , lets go ahead and chunk these in to hex characters:

In []: x = iter('00087F0A')

In []: res = [ ''.join(i) for i in zip(x, x) ]

In []: res
Out[]: ['00', '08', '7F', '0A']

Now if we wanted we could convert these hex codes manually:

In []: int('0A', 16)
Out[]: 10

But we want to do this in one big swoop:

In []: d = [ str(int(i, 16)) for i in res ]

In []: d
Out[]: ['0', '8', '127', '10']

And there we go, our IP address; however, it appears to be backwards. Lets go ahead and fix that, and return as a string:

In []: '.'.join(d[::-1])
Out[]: '10.127.8.0'

And there we have it! Your function may look something like this when all said and done:

In []: def hex_to_ip(hexaddr):
   ....:     x = iter(hexaddr)
   ....:     res = [str(int(''.join(i), 16)) for i in zip(x, x)]
   ....:     return '.'.join(res[::-1])
   ....:

And with output like so:

In []: hex_to_ip('00087F0A')
Out[]: '10.127.8.0'

In []: hex_to_ip('0000FEA9')
Out[]: '169.254.0.0'
DevelopmentPythonLinux