Re: Porting Winsock DHCP Server; is OS/X ignoring Broadcast UDP in recvall()?
Re: Porting Winsock DHCP Server; is OS/X ignoring Broadcast UDP in recvall()?
- Subject: Re: Porting Winsock DHCP Server; is OS/X ignoring Broadcast UDP in recvall()?
- From: Hostile Fork <email@hidden>
- Date: Tue, 12 Feb 2008 18:36:43 -0800
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Well... I'm down to finishing up this piece of code, which has now
proven it works on at least a few linuxes and OS/Xes. It also turned
out that a Fedora Core linux required the packet-level DHCP; it didn't
just send the 255.255.255.255 to all the network cards in the system
when you code at the socket level. It seems like the safe bet is to
just never do world broadcast (sending or receiving) with sockets.
One issue I discovered was that OS/X 10.4 ships with a version of
libpcap that doesn't have pcap_inject or pcap_sendpacket. So perhaps
that's why old darwin code uses the bpf layer to send packets! To
work around that, I just linked the 10.4 version with a newer libpcap
I downloaded and built instead of "-lpcap" and that made the functions
available.
But now I've returned to getting the ethernet address of the network
card from pcap's device handle (it is necessary to stuff into the
packet to send it). So here's the status on that:
On Feb 1, 2008, at 4:26 PM, Peter Sichel wrote:
I'm not too clear about cross platform mechanisms since
this is basically a function of the driver at the data link
layer.
I thought I might have found a sub-optimal (but at least workable)
solution with the function ether_hostton:
http://linux.die.net/man/3/ether_hostton
It seemed like it could be as easy as passing in the IP address of the
adapter as reported by pcap, and then letting the person edit their /
etc/ethers file to make sure they have an ethernet address registered
for the IP. It's a little bit of manual labor, but as it seems to be
common practice it would beat a home-grown INI file solution.
But the function didn't work. I did a little more investigation to
see if had to do with the fact that I didn't have that host in the
DNS, so I tried a little test instead (using the relevant numbers and
not ? marks):
In File /etc/ethers (was empty), add:
??:??:??:??:??:?? testhostton
In File /etc/hosts, add:
?.?.?.? testhostton
Still... a call to ether_hostton("testhostton", ðer) returns non-
zero, indicating failure. This even after running "sudo dscacheutil -
flushcache". So I wonder... anyone ever successfully passed something
to ether_hostton and succeeded? Or know why it would ignore my
entries? The documentation suggests the file is re-read on every call
to the routine... I'm surprised it wouldn't work.
In most UNIX systems, you can use Sysctl to get the
NET_RT_IFLIST and read it from there as described
in Stevens "UNIX Network Programming"
CTL_NET.AF_ROUTE.0.AF_INET.NET_RT_IFLIST.0
This might at least cover other UNIX like systems
(versus the System Configuration Framework
which is Mac OS X only).
Thanks for the pointer! Though for the sake of simplicity/
portability, if ether_hostton() isn't going to work I'm going to self-
send a packet with socket level that I know is going to the right
adapter, capture it with pcap, and break out the ethernet header data
to use later in my pcap_inject calls! :) Hopefully that will work...
---
http://hostilefork.com
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