UDP packets not delivered from USB modem
UDP packets not delivered from USB modem
- Subject: UDP packets not delivered from USB modem
- From: Jamie Curmi <email@hidden>
- Date: Sun, 10 Apr 2005 11:53:16 +1000
Hi All,
I have a USB Modem (actually a wireless broadband CDMA modem). I'm on
a Mac running OS X 10.3.8. The modem has windows software, but nothing
for the Mac, so I'm attempting to develop stuff to work with it on the
Mac.
I can start a PPP connection with the modem, and use the internet fine.
The problem I have is communicating with the modem while in a PPP
session.
The manufacturer sent me details on how to do this. Basically, you can
send commands to the modem via UDP packets sent to 1.1.1.1:33333. And
the modem responds sending UDP packets to 127.0.0.1:33333.
Sending to the modem works fine. Using tcpdump, I can actually see the
packets delivered, and view the return packets with -w (they are
definitely responses, and the modem can be controlled). tcpdump gives
me lines such as:
09:52:32.705221 IP 1.1.1.1.65530 > 127.0.0.1.33333: UDP, length: 13
Showing replies are sent to 127.0.0.1:33333. The idea is that replies
and notifications from the modem should be UDP packets sent to
127.0.0.1:33333, which I can then respond to as needed.
My code listens for these packets, but never sees them. Fearing my
code was wrong, I've tried using nc - via
nc -l -p 33333 -u
But the packets are never delivered. My socket code also seems to
work, as I can manually send packets to 127.0.0.1:33333 and it sees
them. So the packets from the USB modem seem to get lost.
I've tried adding routes, but I've had no luck (tried to copy the
routes the window software seems to add when you run it with this USB
modem, but that made no difference). I just can't seem to get the
packets delivered at all. The firewall is off, so I don't think that
is the problem?
I must admit though, I've never really done much in terms of
networking. So maybe there is something obvious? Something about the
way OS X works that I don't know?
Does anyone have any ideas? I'm getting desperate now, and looking at
a hack using pcap if I can't solve this problem. I'd prefer to do it
the way the manufacturer intended though.
Any help would really be appreciated.
Thanks in advance.
Jamie
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