On a local network I'm sending a WOL (Wake-On-LAN) packet using sendto to the target MAC address. The code for that works without any problems and the target machine is turned on correctly. The problem is, that I don't know if the target machine has a LAN cable attached or not. If it's not attached, then the whole process fails. Unfortunately, sendto is unidirectional, so I don't know if my magic packet arrived.
I'm wondering about the best and fastest way to find out if WOL succeeded or not. Waiting for the device to boot up completely so I find out get and ping its IP address takes way too long.
Is there a way to "ping" a MAC address, i.e. get some sort of Layer-2-reply?
I need this solution for a Delphi application, but if you have a solution for a different language at hand you're welcome to post that as well. Thank you!
Related
My employer has asked me to prepare for testing several thousand Chromebooks (mix of models/manufacturers) to refurb/flip. This may be a recurring thing.
Most or all of these will be old enough that CCD will not be available. I'd like to connect a widget such as a Raspberry Pi to the USB and have it automate testing as much as possible.
I know I can use keyboard emulation to inject commands, but I'd like to get a crosh session running over USB so that I can read info from the DUT besides just controlling it.
Google shows bazillions of returns about using a Chromebook as an ssh terminal but what I'm looking for is the opposite. I'm prepared for the answer to be a simple "no" but I'm concerned because I can't find that anyone else has asked this question. I don't think I'm that creative, so I suspect my Goog-fu is weak.
The answer appears to be "no". However I solved it another way; using "gadget mode" I have a Raspberry Pi ZW enumerate as a keyboard and a serial port. I put the Chromebook into Developer mode, open a developer shell with ctrl/alt/F2, or on a PC/linux or Mac system open a terminal window and type "sudo su" (these have to be done manually). Then I have the RPi issue this bash command to identify the serial port "in the blind":
SERPORT=/dev/serial/by-id/$(ls /dev/serial/by-id) # Chromebook or PC/linux
(or)
SERPORT=$(ls /dev/cu.usbmodem*) # Mac
Now I can have the RPi inject commands via the keyboard, put ">$SERPORT" on the end of each command, and the output comes in the RPi gadget serial port. The RPi then packages the data and forwards it over WiFi to our CRM. It's working nicely for Chromebooks, PCs booted into linux, Mac desktops and Macbooks.
Edit:
The company I work for has actually turned this into a product and so I'm not sure how much detail I should share, but...
I learned my way around gadget mode on the RPi from this link. There are examples for setting up a keyboard and a serial port. Using the templates in that link, I made a device called /dev/hidg0 which emits keyboard scancodes from the RPi to the Chromebook. I also made a device called /dev/ttyGS0 which the Chromebook sees as a serial port.
So I send keystrokes with some python like:
with open("/dev/hidg0","bw") as hid:
hid.write(blah)
and then have the Chromebook send text to the serial port, which I then read by looking at /dev/ttyGS0
Hopefully this will be enough to get you started. I found the isticktoit link very helpful.
I need to slow down (simulate bad) internet connection, I found some documentation where it was achieved by "ipfw pipe" command , the thing is that in latest MAC OS versions , ipfw was deprecated (and removed)...
I was wondering if there are any alternative to the ipfw API ?
Does anyone know how latest Network Link Conditioner achieves it?
The original previous way which enabled to slow down an internet connection :
sudo ipfw pipe 1 config bw 56Kbit/s delay 200 plr 0.2
and to clear the pipe :
sudo ipfw delete 1
Thanks.
I don't know much about Mac OS (I use Linux myself), but I'll give this a shot.
A bunch of digging established that ipfw seems unavailable, as you say.
I was also unable to find a way to use the Network Link Conditioner from the command line. Everything should be usable from the command line, so that's stupid.
One work around would be to try to access the NLC from within AppleScript. The following will get you started on toggling the NLC:
property thePane : "com.apple.Network-Link-Conditioner"
tell application "System Preferences"
activate
set the current pane to pane id thePane
--delay 2
end tell
---
tell application "System Events"
tell application process "System Preferences"
try
click ((checkboxes of window "Network Link Conditioner") whose description is "enable switch")
on error
click ((checkboxes of window "Network Link Conditioner") whose description is "enable switch")
end try
end tell
end tell
I think that you can run a script from the terminal with osascript <SCRIPT>.
As an alternative, Charles Proxy is a pay-to-use program that can be used to perform throttling, provided you can convince the software you are testing to connect to the proxy's port rather than directly to the internet. Maybe there are free proxy solutions out there somewhere?
Perhaps Squid would work in that regard. SquidMan seems to be an easy-ish way to install it for Mac. It looks as though DelayPools and or Client Bandwidth Limits might be useful for simulating a low speed connection, though I can't find evidence of people having used them for such.
I found several solutions that might work. They come from some old threads, but they might help:
How to simulate slow internet connections on the mac
Apple has made a very handy official tool to slow down the network connections on you Mac for testing purposes.
The Network Link Conditioner preference is a free download from within Xcode (for Lion and later OS). Additionally, iOS has similar function accessible from within Xcode and iOS 6 or later.
How do I simulate a bad Wi-Fi connection on my iPad?
There are a few ways you can do this, depending on your situation:
Move further away from your router. While this may seem a bit obvious, I realize that it isn't always possible while testing/debugging (for example, if you are working on a desktop computer).
Put aluminum foil around the router and/or antenna. This will (partially) block some or all of the radio signals by creating a makeshift Faraday cage. The results you get will depend on the strength of your router signal, distance from the router, and other environmental factors.
Set your router's wireless signal power to a lower setting. The method for doing this is different for each router, so you will have to look at the user guide for instructions on how to do this.
Slow down internet for iOS simulator
You can set the network to slow characteristic by testing on devices. Go to Settings -> Developer Settings -> Network Link Conditioner -> Enable. This is for iPhone/iPad running iOS 6
I don't know if the last one you can still do.
I've used many methods in the past for slowing down network connections, among them:
performing a parallel download of some massive Linux ISO file;
physically pulling out the Ethernet cable (at one point, I actually toyed with the idea of building a push-button device that would sit between two cat5 cables and do this without having to physically disconnect the whole cable).
using ifconfig eth0 down ; sleep 1 ; ifconfig eth0 up.
Hopefully one or more of those methods will help.
If you're looking to slow down your network connection because you're doing testing/profiling work, one option is to get a specific device that can create network latency/noise.
For example Apposite Tech's mini2 WAN emulator allows you to change values for bandwidth and packet loss. You can roll your own device too using something like: http://wanem.sourceforge.net/ . It just depends on your needs, time and budget.
I'm trying to get a very old, but working great C2001A/J4100A (HP LaserJet 4) to work with the HP Linux Imaging and Printing library, but I'm having an awful time of it.
1) There's no entry in /usr/share/hplip/data/models/models.dat for [hp_laserjet_4]. This is the first problem so far when I used Bonjour discovery through an avahi.service file I put on my OpenWRT router. I don't currently have an iPhone I want it to discover with AirPrint, but this is how I started off and helps CUPS finds printers anyways.
2) SLP discovery is a complete bomb. I've traced it down to the UDP packet the JetDirect sends off in response to the broadcast discovery request. The part that is 'x-hp-p1=0' should be something like 'x-hp-p1=MFG:HP;MDL:LaserJet4;etc..' and it causes hp-probe to fail to see what printer the JetDirect is plugged into.
I can't seem to force HPLIP to bypass the bad discovery methods and it's too smart and wants to verify.
I've posted to the HPLIP help area, but they seem to run a week slow.
Instead of doing JetDirect, try LPR directly to the IP address. And any of the older PCL drivers should work against that printer.
On our team we have a standardized development setup where we have a Win8 workstation with various VMs running on Hyper-V. All development takes place on a VM.
I was having an issue where I couldn't check out a project from a Team Foundation Server using VS2012, it would start checking out, but then the connection drops. I fired up Wireshark to check what's happening, but then it worked fine. I double checked:
When Wireshark(or rather WinPcap which is doing the actual capture), running on the workstation, is capturing packets from the VM's virtual NIC, everything works fine.
As soon as I stop the capture, TFS can't check out.
So I can't even properly inspect the network traffic to diagnose the issue, because the act of inspecting traffic changes it. Heisenberg would be proud!
I thought it might be an issue with Wireshark overriding some check-sum offloading settings, but it seems not to be the case.
So what else can be affected by running Wireshark? I rather thought that the point of packet sniffers is that they don't change the packets as they capture them.
That means you are picking traffic that normally would not be picked by the vmnic.
Try to check on mac address level what is happening. Maybe mac address conflict between VMs ?
ps. You can whireshark without promiscuous mode. The the Heisenberg rule should not apply :)
Looking at this related SO question, I can't help but wonder about the uniqueness of MAC addresses.
How unique are MAC addresses?
I'm using them to semi-uniquely identify users. I have a website that users of virtually any device (PC, Mac, iPhone, Android phone, etc.) and any OS can hit via an HTTP request. I use a combination of IP address and MAC address to identify unique users.
I assume the following cases can exist:
A device has no MAC address (unlikely, sure, but anyway)
A device has a unique MAC address
A device has multiple unique MAC addresses
Two or more devices have the same MAC address
The first three of these cases are unique (the third because I only need a single unique MAC address). For the fourth case, how likely is this?
That is: given 100 random users (perhaps Windows users for any Windows OS), how many of them can I expect to have the same MAC address? Is it just generally because of the limited length of MAC addresses? Or is it dependent on some sort of purposeful configuration change (MAC address spoofing)?
I'm okay with MAC addresses being semi-unique, I just want some clarity on how to interpret the data.
(I'm using the C# code against .NET 2.0 in the linked question against .NET 2.0.)
This is only true on the same network.
MAC addresses are resolved locally using ARP to route local packets at a hardware level. ARP is not a routable protocol and is not resolved across subnets.
If your webserver is behind a router with port mapping and all the incoming traffic to it is coming from that router, then every connection will appear to come from the MAC address of the router, you won't 'see' the MAC address of the original machine, not unless you can pick it up with a web page somehow (i'm not a web genius so don't ask me on that one, but Im guessing you'd need some heavy lifting at the client end with Java, or some other kind of active component to interrogate the local machine, easier to use a cookie)
You can find out the Public IP address of the remote machine where the outgoing NAT took place, but once again, there could be multiple device connecting from behind a router which would limit the usefulness of this method, and it means need to look into IP packets, which I have no idea how you can do that from a web server (probably can't?).
Anyway, this is what cookies are for, a way of leaving an identifier on a remote machine so you can see where traffic came from. If people don't accept cookies, unless you start getting very very creative you aren't going to be able to uniquely identify them.
(BTW Mac address are always unique (ok, you can occasionally find a reused MAC, but its extremely rare, or at least needs to be for networking to work!), thats the purpose of them, it's just not much help in this scenario if you are not on the same network)
100 random users (perhaps Windows users for any Windows OS), how many
of them can I expect to have the same MAC address?
Zero. And when they are in the same network, they could not communicate with the same MAC-Address, since Ethernet uses them to find the Computer. They are pretty unique. Producers of network cards get ranges of addresses they may assign to their products.
But: There are ways to manipulate your MAC Address, and there are scenarios where people do just that! For example when you want to enter a network, which is restricted to certain MAC-Addresses, you can manipulate your own to match one of those (if you find out, which ones are on the whitelist). Since I don't know, what your szenario is, (what you wnat to accomplish), I can not tell you if that is relevant for yout.
You just need to understand the difference between a MAC Address (that can be changed) and the identifier of your hardware [your Network Interface Controler to be precise] (that is forever assigned by its the manufacturer).
MAC address is the name of your device when it connects to the internet (through a rooter or a switch). You can change your MAC Address, but by default, this ID uses the identifier assigned by the manufacturer of the network interface controller (NIC) (e.g. your Wifi antena)
Exemple: I've changed my MAC address for my two computers using the same MAC Address: 00:01:02:03:04:06. My computers seems to be the same when connected to the same router but the identifier of their wifi antena remain unchanged and different.