Does DDS communication works between 2 computers in different networks? - networking

I am quite new to DDS. I am using ROS2 which is built on DDS. I want to run a ROS2 based publisher and subscribe to a RTI Connext based Simulink model both located on different PC's.
I want communication between 2 different PC's.
Questions :
Should both PC's be located in the same network.
Should multicasting be enabled ? Multicasting is blocked in my company's network. Is there an alternative to this ?

Yes, both PC must be under the same network.
Multicasting is used for the discovery of the nodes in ROS2.
If your company does not provide the necessary networking support, you can always try to build your own. For example you can use a switch and connect both PC to it.
Or you can use your phone. I created a hotspot with my phone with 4 devices connected to it and communicating using ROS2.
However, if you need to have access to the company network, ask your IT department if they can set you up with a switch connected to the network that has multicast :)
Edit: As specified in another answer, it is possible to do a static discovery. However, this would imply modifying the ROS2 configuration of the RTI Connext RMW> https://github.com/ros2/rmw_connext

If the computers are on the same network, and multicast is enabled, and the multicast TTL is high enough, and the computers are publishing/subscribing on the same topic on the same domain, and their Types and QoS are compatible, then they should automatically discover each other.
If multicast is disabled, you can tell the DDS participant to use a specific address to peer to (see the docs for "initial peers"). This can be done in different ways. Here's a good reference: Initial Peers

Related

Can devices using different cellular technologies (like a 3G & a 4G device) be on the same (cellular) network?

So I my ISP assigns local private IP address to devices on the network, I found that by checking the IP address assigned to my phone's ccmni0 interface which I believe is the one used to connect to the network.
And so I tried sending a message to my other phone (which uses a SIM card from the same network provider as the other, so I assumed they are on the same network) using the local IP assigned to it. I was expecting to receive the message on the device but didn't, that's why I suspect the reason might be because they use different cellular technology (one 3G and the other 4G).
Please tell me if my suspicion is true or not. And guide me if I have done anything wrong.

Using a physical network adapter on VMWARE

I just have a server with 2 PCI and 3 PCIx network adapters (offboard of course) already installed. I´d like to use them inside the Virtual Machine that VMWare creates...
I read about it, and as long as I know it´s just possible to use a external network adapter if it has an USB connection.
Do you know any way to do it that I`m trying?
It´s for a use in a specific video system which requires different vm´s and network adapters.
Tks a lot.
Lyniker Aoyagui
There are multiple ways to achieve it. First is to use physical interface state replication, which you can enable in Network adapter entry in Hardware tab of your VM. With that it will treat hardware interfaces just as if you've plugged them directly into the VM.
Other way to go about it, and one that doesn't require hardware network adapters, is to utilize quite robust Virtual network editor (Edit->Virtual Network Editor) which should allow you to replicate most networking conditions you will need.

Detect all networked devices' types in a home network

I would like to write a software running in a networked device, i.e. PC. It can automatically detect the other network devices' types. For example, it can detect there is a PS3, a Wii, an IPad running in the same network. Any ideas? Thanks,
You have two problems: first, detecting that a device is connected to your network and at 192.168.1.x. Second, somehow detecting what that device is.
The first is easy-ish to accomplish: there's discovery protocols like UPnP and Bonjour. However, in a home networking scenario, the easiest and most reliable way to get a list of connected devices is probably to pull the DHCP reservations from your router. You might have to scrape data from the router's HTML-based management interface—hacky as that may be—but it would work. (If you're using .NET, consider the HTML Agility Pack to accomplish this.)
Once you have a list of IP addresses of connected devices, your next problem is to figure out what each device actually is. This will be more challenging. Some possibilities:
You may be able to use the MAC address to help detect the device's vendor. (Here's a list.)
If you're using UPnP, you can ask the device what it is.
Use IP fingerprinting to determine what the device is.
Couple thoughts. The broadcast IP address - 255.255.255.255 is where devices talk and say "here I am". Should be able to listen to this and find ip addresses and more. Second, if devices are assigned an IP address by a DHCP client (obviously) you can usually find a list on the dhcp device. Devices often have names, this is a higher level protocol, like windows SMB, that you may have to interface with in order to get that information.

Peer-to-peer chat

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!).

How do I get a MAC address for a remote system when I only know it's IP address?

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

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