I'm new to ROS, wish someone can answer my stupid question.
I have a static IP 140.113.xxx.xxx, and a 4G dongle with floating IP 192.168.8.100. I want to use ROS to transmit data between them. Can ROS do that? Because I found some website said ROS can only transmit data in the same Internet domain, but I think this must have some trick to solve this problem.
this has nothing to do with ROS.Theses are IPs in two different networks, you either create a propper routing or you give a second device an IP in the same net. However 192.168.x.x should not be used in the internet or any other non private networks
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I am person trying to learn networking. I understand that this may not be the best first step to take, but I am eager to try and understand how this takes place because it has been tearing up my mind for quite a while now.
My question is, how does a network recognize a device and automatically connect it to the network?(This is assuming, of course, that you have connected to the network previously and are connecting wirelessly.)
Does it store it on the routers side and then look for specific MAC Addresses and then connect it? Or is it stored somewhere on an encrypted file on your computer? Or is it none of these? Please forgive me if I am way off, I am only giving guesses from what I have so-far learned from networking.
'Connect it to the network' doesn't really mean anything, other than just plugging it in, or turning it on in the case of Wifi. What really happens is that the device broadcasts a DHCP request for an IP address, or else It already has an IP address in that subnet. From that point on it is discoverable by ARP, so other hosts in the subnet can send to it.
Not sure if I should ask this question here, but this is a technology community so why not.
I'm running a local network which is setup like this:
Modem -> Access Point -> Switch -> Server/5 other computers
and my problem is the 5 other computers only two computers can have access to the internet (which are connected though Ethernet).
Also, any device that's connected to my wireless network can't access the internet either.
I know it's not a problem from my ISP since two computers are connected to the internet. And I know it's not a wireless problem since my local server can be reached though the access point.
I'm not sure what is the problem since I replaced all the cables, devices, and done tons of resets.
Appreciate your help, or direction to where I can get help.
Thanks all, but my problem was that I used static IP and didn't assign more than three, two computers and a printer. completely a beginner's mistake.
I don't know if you are familiar with computer networks but I think it's a network problem. Maybe your router (modem) can provide only two IPs and that's why only two computers can connect the internet. To verify this you can check what is your IP, and what is your Subnet Mask. Type ipconfig in your cmd and give me your IP and the subnet mask to check if this is the problem or not.
im wondering if it's possible to create p2p chat application without server(so there is no need in external static ip.Is it true?)?
EddieC is right if the computers are located inside the same sub-network (LAN) or if the computers'ip is their interface to the Internet (WAN public ip). In that case, you can just use the ip's and ports directly.
However, usually, knowing the computers ip is not enough because the machines are located behind routers inside sub-networks. Thus, because the computers are hidden behind the routers, you will have to configure the routers to foward the packets to the right computers as function of the ports used.
Have a look at : http://wiki.vuze.com/w/Port_forwarding
If you do not want to use ip's because they are dynamic, you can configure urls with Dynamic DNS services.
Good luck
It is possible. But you must have someway for one computer to tell the other computer what their IP number is. You could email it to your friend or call them on the phone or post it on a message board.
If this program only has to work on a local network (LAN), there is something called broadcasting which might be of interest to you. It allows a packet to be sent out to every device on the network without having to know their IPs (then other instances of your program could reply with the IP of their machines so you could set up proper connections).
This won't work over the internet, though (imagine being able to broadcast to every computer connected to the internet!).
I'm working on a Wake on LAN service that will run from a web site and should interact with many different platforms - therefore, no Windows-only solutions. When a user registers their system with the web site, I need to get the MAC address to use in constructing the "magic" packet. I have a Java Applet that is able to do this for me and am aware of an ActiveX control that will work, but I'm wondering if there is a way to do this server-side by querying routers/switches. Since the system may be on any of a number of different physical subnets, using ARP won't work -- unless there's a way to configure the router(s) to perform the ARP on my behalf.
Anyone know of any network APIs, proprietary or otherwise, that can be used to look up MAC addresses given an IP address? I think we're using Cisco routers, but it's a complicated network and there may be multiple vendors involved at various levels. I'd like to get some background information on possible solutions before I go to make a sacrifice to the network gods. No point in abasing myself if it's not technically possible. :-)
EDIT: We do have the network infrastructure set up to allow directed broadcast, though figuring out the exact broadcast address since netmasks are not always /24 is another conundrum that I need to solve.
If you are on a local network that uses DHCP you might be able to look in the servers database to get the MAC of the last user with that address. In the future you could watch the network for ARP requests and cache the responses in some sort of table. You might also look at using RMON or SNMP to try and query the Address Tables on the switches and routers.
It should be noted that to use WoL across routers you either need to enable Directed Broadcasts or you need to have a relay server in the local segment.
Been a while since I played routers and swtiches but this might be a starting point for what to query using SNMP http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a00801c9199.shtml
Use the following:
getmac /s destIp
To get the remote session Mac address.
I don't know if these might be helpful but take a look:
http://www.webdeveloper.com/forum/showthread.php?t=134120
http://www.qualitycodes.com/tutorial.php?articleid=19
You've said everything I can think of...
The source MAC address changes as a packet hops from device to device so unless the client is on the same subnet, the server won't be able to get the MAC address. (You would do it via ARP)
A signed java applet or activex control would be the easiest solution. It would be able to (almost passively) get all the networking info you need (IE doesn't even prompt to run a signed applet)
If you are fully aware of the network that is using the service then you could probably query a gateway's client-list via SNMP or CDP. You would be able to map out IP-Addresses to MAC addresses... but this is really vendor dependent (but common) and wouldn't be much better (imo) than having an applet.
Currently the application is using a Java 6 applet that allows me to extract both the hostname and the MAC address from the remote system. I don't like having this dependency on Java 6, but Snow Leopard and Windows both support it, so I can probably live with it.
On a related-front our networking folks approached me for some help with converting some existing code to ASP.NET. During the conversation I asked if they had live MAC address information (since they do port shutoffs based on suspicious network activity -- viruses/worms). Turns out they do and we may be able to leverage this project to get access to the information from the network database.
I don't think there is any way to accomplish this. When the IP packet goes via the first router the host's MAC information is lost (as you know MAC is only used in ethernet layer). If the router most close to your PC was capable of telling the remote MAC code to you, again it would only see the MAC of the next router between your PC and the "other end".
Start sacrificing.
There's no general way to do this in terms of the network unless you have no routers involved. With a router involved, you will never see the MAC address of the originating system.
This assumes that the originating system only ever has a single network interface, so has only a single MAC address.
In fact, are you even sure that your "magic packet" (whatever that is) will reach the system you want it to reach, through the routers? That sounds like a function the routers or other network infrastructure should be performing.
Mac address is only used on network segments, and is lost at each hop. Only IP is preserved for end-to-end - and even then the from ip address is rewritten when Natted. I guess my answer is, not possible unless everything is on the same network segment, or your routers are set up for proxy arp (which is not really realistic).
You can only get MAC entries in the ARP table for machines on the same network. If you connect to a machine via a router then you will only see the routers MAC address in the ARP table. So there is no way of knowing the foreign host’s MAC address unless it's a host on the same network (no routers involved).
And by the way there are many similar question already on SO.
if it's a windows system you can use NBTSTAT -A
this will return the netbios info and the IP is there
any Management system like SMS or Altiris will have this info
The DHCP server is a good idea
If it's local you can ping it and then quickly run ARP -a
look for the IP and the MAC will be there.
you might need to write a small batch file.
if you have access to the PC you can use WMI to access the info for the Nic with DHCP.
As said above we can get mac address from a known IP address if that host is in the same subnet. First ping that ip; then look at arp -a | grep and parse the string on nix* to get mac address.
We can issue system command from all programming languages standard API's and can parse the output to get mac address.Java api can ping an IP but I am not sure if we parse the ping output(some library can do it).
It would be better to avoid issuing system command and find an alternative solution as it is not really Platform Independent way of doing it.
Courtesy: Professor Saleem Bhatti
There is a lot of history here, so please bear with me.
Our home network used to be fine when we were with Comcast, but we wanted better speed and reliability, so we switched to FIOS. At that point, the Wifi connections from my Raspberry Pis stopped working. I got frustrated after a couple of weeks of trying to discover the cause of the problem and eventually put it aside.
The other day, I started to configure a new Raspberry Pi 4 that I plan to use on my new Sphero RVR. I set it up following the usual directions and the Pi connects to the Internet without problem over WiFi, but I can't ping it from my Windows 10 desktop.
So I started digging. I downloaded the Fing app onto my Pixel 3 Android phone and looked at the network. I immediately noticed that all the devices now have a 10.29.179.xxx addresses. That easily explains why I can't ping from my PC to the Raspberry Pi. They aren't in the same address space.
I did discover that I can ping the Raspberry Pi if I use the IPV6 address. I can even get PuTTY to connect using the IPv6 address, although I was unable to successfully login. I don't know what is causing the login problem, but it's probably something mundane.
I suspect that I can make my Rpi conform to the rest of the network using a static IP address, but that might cause problems if I take the robot somewhere else to demonstrate what it can do. What I would like to understand is why most of my network, using DHCP, is on the 10.x.x.x network and the Raspberry Pis seem to wind up with 192.168.1.xxx addresses.
One further wrinkle. We have two routers, the FIOS router, and a LinkSys WRT1900AC, which is the router on which WiFi is enabled.
I suspect this problem is caused by having the two routers or by something inherent in the way the Raspberry Pi interacts with DHCP.
I would like for my Raspberry Pi to configure with an IPv4 address I can use, no matter what network I am connecting it to, and I'd like to understand why this problem is happening in the first place.
Let me know what additional information you'd like to see.
* Additional Notes *
As to the comment that I have not done research. I spent a week reading through stackoverflow problems and reading up on documentation of DHCP without finding the answers to my question. I do not ask questions idley. I ask questions when I cannot find answers and need the help of people more expert than myself in the areas in which I am having trouble.
I have solved the login problem. It was a stupid password mistake.
So now I can login, over wifi, using the IPv6 address, but not with the IPv4 address.
On the FIOS router, both the 2.4 and 5GHz wifi channels are turned off.
As suggested by Ljm Dullaart, the problem was that there were two DHCP servers on the network. After I turned off the FIOS DHCP, my problems went away.