im new to linux environment and any help/feedback would be appreciated. Im actually trying to develop a client-server (MULTICAST) program, so, i would like to test one client sending information to different servers (one-to-many relationship). thus, i would like to simulate different server side in linux with different IP addresses in one computer.
Did you try using different ports instead? I didn't try it myself, but perhaps that can help you in the mid-time.
If you're really multicasting, you don't need to worry about physical host-specific IP:s, all you should need to do is make sure all the programs (clients and servers) are using the same multicast group addresses. Then they should all see each other's traffic automatically.
There's nothing stopping you from running multiple clients on the same machine that also runs the server, in this case.
I sounds like you want to test your code with different IP's. You can create IP aliases on your interface and simulate multiple IP's on one computer.
for e.g. if eth0 is you're active interface with IP, say 192.168.5.11 you can assign another IP to eth0:0 (an alias to eth0) as below.
ifconfig eth0:0 192.168.5.12 netmask255.255.255.0 up
ifconfig eth0:1 192.168.5.13 netmask255.255.255.0 up
run your server on one of the IP's and distribute clients to all your aliases
Use either of the following when you do not have sufficient hardware:
Multicast loop which has the IP stack redirect outbound packets to local receivers.
Virtual machines.
Be aware that semantics of the socket option for #1 change depending on the operating system; for #2 only some virtual machines support multicast, refer to the vendor for details.
http://msdn.microsoft.com/en-us/library/windows/desktop/ms739161(v=vs.85).aspx
Ultimately though you must test with different machines due to specific artifacts of how hosts manage multicast groups. You can for instance create send-only membership which will block every other application on the host. Also consider that an internet, lower case 'I', will introduce further artifacts regarding group joining and propagation delays and drops that your application may need to be aware of.
You can create multiple IP for same machine with help of IP alias. As mentioned above.
But to create multiple Server at one PC you must need different port for each server if you want to simulate the all server behavior with network as well.
I mean for one port multicast traffic always goes to that and some process in the PC will be receiving the packet and has to serve for all server in the PC, Means you have one packet only and all server is receiving with locally manipulation.
But really simulation would be you have multiple server at 1 PC and all are receiving multicast traffic from network rather then from local process.
my Solution: You keep number for server == number of port at the PC. Client send the multicast traffic over all port simultaneously and all server at the PC end will be receiving multicast packet from corresponding port from the Network.
Please correct me if my understanding is wrong.
Related
I have two laptops, both running Ubuntu.
I want to write a chat server in C, which can talk to my other laptop and receive messages back from it.
I know that when the client and server programs are both in a single machine, I can use local host (127.0.0.1) and make them talk using telnet but what about connecting two different computers (which are on the same network)? Which IP and port should I use for them?
A is the Server with IP[A] address (ex: 192.168.1.2)
B is the Client with IP[B] address
So on your chat Server on A at some point in the code you will open a port, you will specify a port number to open. If the number of the port is X then on the client you will connect to IP[A]:X
To give you an example with X=4444, you will open a connection like: 192.168.1.2:4444
Regards,
Basically all that you need to make sure as far as a port goes is that the port is not already in use by another service. There is a number a ways to do this, but I suggest you start by looking at commonly used ports.
As far as IP goes, you are going to want to determine if you want to use the public or private IP of the machines that you are attempting to connect. If you are using the public IPs you will probably have to set up port forwarding in some capacity. If you are just connecting two private ips (i.e. the one the same network) then you don't need to port forward.
Ultimately, this issue is highly specific to you use case and we would need more information to answer it for your exact case.
I am trying to find out whether the machines in a network are running a certain app. More like, I am trying to resolve addresses of nodes in a network.
I built a small code based on ARP, but it works only on a local network(same subnet). What I want to do is resolve addresses out of the subnet i.e. all other nodes.
I read these answers: UDP broadcast packets across subnets
and Broadcast on different subnets
But they all talk about changing router setting or creating a multicast network.
From what I read for multicasting to work, I need to create a multitask network beforehand. Is it really necessary?
And for changing router setting, does it really have to be a "special" router?
This is all for a college assignment and would be demonstrating it probably on an ad-hoc network or something like that.
I am open to ideas to solve the original problem.
PS:
1. I am a beginner in networking so do excuse me for any fault or misinterpretation.
I am using sockets and C(No other option).
Edit 1:
I am well aware ARP is useless outside the subnet. I mentioned it because I used it and it helped explaining the problem.
Edit 2:
The original problem is:
Building a chat application, nothing fancy sending messages from one point to another, without using a central server of any kind. Not even a hybrid network with a central store is allowed.
i.e. if A and B are two clients, A should directly connect to B and vice versa.
I did some research and decided to use P2P architecture. And now I am stuck to how will A discover address of B. If I know the subnet of B, I can brute force and locate B but since I don't have such information what do I do?
ARP is not intended to be routed outside the local network, where in IPv4, the "local network" typically corresponds to a subnet. You should not expect ARP traffic to transit routers from inside to outside or vise versa.
Similarly, UDP broadcasts generally do not propagate outside the local network, and it's a good thing that they don't, for reasons related to both security and traffic volume.
From what I read for multicasting to work, I need to create a multitask network beforehand. Is it really necessary?
Basically, yes. Your routers need to be configured to support multicasting (which may be their default). All participants need to agree on and join the same multicast group. There might not be a need for any new networking hardware, but multicast communication has its own protocols and network requirements; it is not merely a broadcast that can traverse network boundaries.
And for changing router setting, does it really have to be a "special" router?
If you mean changing router settings so that UDP broadcasts are routed between networks, you do indeed need a router that exposes this capability. But I urge you not to do this, as it will let broadcasts from all other sources, for all other reasons transit the router, too. At minimum, this will significantly increase the noisiness of all networks involved, but it could produce bona fide misbehavior of applications and services other than yours.
The Limited Broadcast (255.255.255.255, which is used by ARP requests as the destination address, and ARP only works for IPv4 on the local LAN) cannot cross a router, and a Network Broadcast (last network address, where the host is all ones) by default cannot cross a router (Directed Broadcast) because it is a security risk (see RFC 2644, Changing the Default for Directed Broadcasts in Routers).
Some routers can be configured to forward directed broadcasts, but this can be dangerous.
Multicast is a form of broadcast. Multicast routing is very different than unicast routing, and every router in a path must be configured for multicast routing. Also, hosts must subscribe to a multicast group before they will even listen for packets from a multicast group. Additionally, there are some multicast groups that all hosts listen for, but those are link-local multicasts that cannot be forwarded off the local LAN.
Adding to what other answers have provided:
ARP is not useful for a system in another subnet. Even if you were able to send an ARP request to a system in the other subnet, and receive its response somehow -- providing you with that system's MAC address -- you could not use it to send a packet to that system because Ethernet does not provide a routing mechanism, and so the system will never see any Ethernet packet you address to it.
If you are simply trying to identify which systems within another IP subnet are live, you can probably do this by other means. Take a look at the nmap command, for example. It supports a wide variety of IP communications methods that will be routed to the other subnet and can often detect what machines are present and which services are available on the machines found.
And you can of course duplicate what nmap does yourself. For example, if you want to find out which systems in subnet 192.168.10.0/24 are listening on TCP port 80, one way is to simply attempt to connect to port 80 on each system in that subnet. In general, there are four answers you may receive back:
Connection success (No error: the machine is present and there is a program listening to that port)
Connection refused (errno ECONNREFUSED: the machine is present but there
is no program listening to that port)
No route to host (EHOSTUNREACH: there is no machine answering to
that IP address)
No response (ETIMEDOUT: several reasons why this can happen; for example, the system could have firewall settings causing it to simply ignore the request)
(And there are other less likely possibilities as well.) Using other IP access methods (ICMP/ping, UDP packets) will have a different matrix of possible results.
As others have explained, multicast mechanisms would only be helpful for discovering a set of cooperating machines that are pre-configured to join a multicast group.
I am able to run a client and server on the same computer on two different terminals in Linux. Now I want to run the same model on two different computers. I am guessing there is more to this than just changing the IP address and the port number to that of the Server.
Any guidance on the matter is highly appreciated.
Thanks.
Make sure the port is forwarded in your router and exceptions for the port is added to the firewall. Then you should be ready to go!
If you have the computers in the same network you can do it without forwarding your port.
I have a course project where I'm suppose to present some networking stuff. There are great chances that I have to do it on one computer. So my question is, how do I show a communication between tcp/ip or tcp/udp? I'm not a networking expert, I understand the concept of sending data which is red. And I think I need two IP addresses.
You don't need two IP addresses. Just start the server on the machine, and have the client connect to address 127.0.0.1 and the appropriate port. (This address always refers to the same machine the program is running on.)
You can run a virtual machine on your computer and work on network between them.
I'm learning C socket programming. When would you use bind() on the client-side? What types of program will need it and why? Where can I find an example?
On the client side, you would only use bind if you want to use a specific client-side port, which is rare. Usually on the client, you specify the IP address and port of the server machine, and the OS will pick which port you will use. Generally you don't care, but in some cases, there may be a firewall on the client that only allows outgoing connections on certain port. In that case, you will need to bind to a specific port before the connection attempt will work.
An example would be the data connection of an active FTP connection. In this case, the server connects from its port 20 to the IP and port specified by a PORT or EPRT command.
A classic example of a client program using bind() is the (obsolete) rlogin / rsh family of network clients. These clients were intended to be used within networks with strong trust relationships - in some cases the server machine trusts the client machine to tell it the username of the user that is connecting. This required that the client program connect from a low port (a port less than 1024), because such ports are restricted to the root user and thus (in theory) prove that the client being used is authorised by the system administrator.
The NFS protocol has similar trust relationships, and similarly the client makes connections from a low port number, using bind().
Another example is IRC clients that allow the user to specify a particular source IP address to connect from. This is to accomodate users with many IP addresses assigned to their machine, each with a different "vanity" domain name assigned to it. Choosing which IP to connect from (with bind()) allows the user to choose which domain name to appear as on IRC.
A good situation would be in a p2p case, you’re communicating with a STUN Server with a bound socket, and the STUN Server tells you the port on which he is receiving messages from your socket (that can be different from the one you specified when you bound your socket depending on your network and more specifically on your NAT type). This will allow you to be aware of the real port translation that your NAT is doing, and you’ll be able to give this information to potential peers that want to connect to you.
Binding the socket is useful as some NATs are dynamically giving you ports (binding on port x twice might not give you the same “real” port). So you’ll be able to directly use the socket you bound to listen on the port.
I suppose you should bind() in the case of UDP sockets.
bind function is one of "key" functions. It associates your socket (server or client) with address (ip + port). As for Windows you must use bind for WinSockets. There is good book about it "Network Programming for Microsoft Windows" by Anthony Jones and Jim Ohlund.
Bind can be used to attach names to a sockets. Thus, say you create a software that uses a particular TCP port, you need to bind it and then, you will know the TCP port it is using.