I know the answer to this question theoretically, but I want to know where to access the info in code level.
So let's say in the example rpl-udp, when the client sends a message to the server, theoretically as we are using rpl to route the message will go through the client's parent, up to the DODAG tree until it reaches the server.
What I want to do it to trace this app level packet as it goes up the tree, all the nodes that relay this packet, I want to know when they receive the packet and when they route it up to the tree.
Where can I find this info in the contiki-ng code? I assume it's not in the RPL header files, but I'm not sure.
Any help would be great.
Thank you.
RPL takes care of route management. The actual packet forwarding is separated from routing protocols, this is a common design pattern in all operating systems.
In Contiki-NG the forwarding code is located in os/net/ipv6/. The main file is tcpip.c. The route data structures and related functions are defined in uip-ds6-route.c and uip-ds6-route.h.
There is also an option for source routing in Contiki-NG, in which case the list of nexthops is directly stored in the packet's IP headers, and the normal IPv6 routing table is absent. The source route table (only present on the root node of the network) is defined in uip-sr.c.
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I am trying to write a simple client-server application where a client can send or broadcast a message to one or all clients in the network. The server stores all IP addresses that are connected to it, and broadcasts a new IP if a new client connects itself.
I'm not quite sure how to implement the sending of a single message to another client. Would I just have to send a TCP message to the server and put the desired recipient as data in the TCP layer which is then extracted by the server so it knows where to send it?
I also want to add encryption to the messages which would then no longer allow the server to read the data, so I'm not sure how to solve that!?
I am using c++ and Qt5 for the implementation
I'm not quite sure how to implement the sending of a single message to
another client. Would I just have to send a TCP message to the server
and put the desired recipient as data in the TCP layer which is then
extracted by the server so it knows where to send it?
In an ideal world, the clients could talk to each other directly, since they could find out the IP addresses of the other clients from the server (either via its broadcast or by requesting a list of IP addresses from the server). If all of your clients are running on the same LAN, that can work well.
Assuming you want your system to run on the general Internet, however, that won't work so well, since many/most clients will be behind various firewalls and so they won't accept incoming TCP connections. (There are some ways around that, but they require a very advanced understanding of how TCP works, and even then they only work in certain situations, so I don't recommend attempting them in a first project)
Therefore, for a reliable client->client messaging mechanism, your best bet is indeed to have the sending client send the message to the server, along with some short header that tells the server which other client(s) the message ought to be forwarded to. My own client/server messaging system works along these lines, and I've found it to work well.
I also want to add encryption to the messages which would then no
longer allow the server to read the data, so I'm not sure how to solve
that!?
Don't worry about adding encryption until you've got the basic non-encrypted functionality working first, since encryption will make things much more difficult to debug. That said, it's perfectly possible to pass encrypted/opaque data to the server, as long as the aforementioned header data (which tells the server where to forward the message to) is not encrypted (since the server will need to be able to read the header to know what to do with the encrypted data). The trickier part will be when the receiving client gets the forwarded data from the server -- how will the receiving client know how to decrypt it? You'll need some external mechanism for clients to share keys (either symmetric keys or public/private keypairs), since if you sent the encryption keys themselves through the server, there wouldn't be much point in encrypting anything (since the server could retain a copy of any keys it forwarded, and use them to decrypt, if it wanted to)
First, I want to give thanks for that amazing lib! I love it. A client is connecting himself to a server. The server should save the IP and do stuff with it later on (I really need the IP). I found that answer: http://lists.zeromq.org/pipermail/zeromq-dev/2010-September/006381.html but I don't understand how I get the IP out of the message (a XREP)... I think I am only able to read the ID, but the IP is managed internally by 0MQ. His second solution suggests to send the IP as part of the message, but I don't understand how to get the "public"-IP. I found that post: Get TCP address information in ZeroMQ
is pass bind a service to an ephemeral port, get a full connection endpoint ("tcp://ipaddress:port")
I don't get how this works. Does he mean something like a web-service?
In my opinion, it would be best to get the IP out of 0MQ (it has the IP already). I would even adjust 0MQ for that, if somebody could point to the place where the IP is saved, couldn't find it. The socket types are not that important, at the moment. I would prefer smth REQ-REP like. Thank you!
Summary:
TL;DR answer to your question is: you can't get IP address of the peer that sent a message, using ZeroMQ API.
Explanation:
ZeroMQ does not expose peer IP address because it is irrelevant for the message based communication that ZeroMQ is designed for. When it is possible for ZeroMQ to get IP address of client that is connecting to server (in example using method described here), it is useless. For a longer explanation here is how it works inside ZeroMQ and any other server implementation.
Server side of the connection does not handle connected clients by the means of the hashtable that maps IP to client, but by keeping track of connected "sockets" (socket descriptors) - when a server accepts (using accept()) a connection, it receives from operating system socket descriptor to use to communicate with connected peer. All server has to do is keep that descriptor around to read() from and write() to that client. Another client that connects to server receives another socket descriptor.
To summarize: even if ZeroMQ would be able to provide you with IP of connected peer, you should not depend on it. ZeroMQ hides from you connection management so you can focus on messaging. Connection management includes reconnections, which may result in a change of IP without changing the actual ZeroMQ socket connected on the other side.
So here's an example of why you might want to get the ip address a message was delivered from: we have a server whose job it is to synchronize updates onto occasionally-connected clients (think mobile devices here, though this is an extreme example of a mobile deivce.)
When the mobile unit comes onto the network, it sends a list of it's firmware files to the server via a dealer-router connection. The server has a list of all applicable firmware files; if the client needs an update it will initiate an update via a separate mechanism.
Since the IPs for the devices can (and do) change, we need to know the IP address associated with the mobile device FOR THIS CONNECTION, i.e. right now.
Yes, we absolutely can have the client send it's IP address in the message, but that's a waste of another n bytes of valuable satellite air time, and while not pure evil, is sure annoying. Zmq already has this information, if it didn't have it, it wouldn't be able to generate replies. The address is in the socket data, there's no reason the message couldn't (optionally, for all you guys who use wired networks and think disconnects are the exception) include a reference to the socket structure so you can get the address out of it. Other than pedantic religiosity, which is far too common in zmq.
The way ZeroMQ is designed there's no information provided on the remote IP. As far as I know you have to manage this through your application by sending that information as a message of some sort.
The messages themselves use an IP-agnostic ID which has more to do with the instance of ZeroMQ running than any particular interface. This is because there may be more than one transport method and interface connecting the two instances.
I am writing a program that needs to create an ad-hoc network. Once it's created and other nodes connect, i need a way to determine the ip of every node on the network (or some other way of forming a connection. I would prefer to use tcp and/or udp, but I don't have to). Once I have a way to connect to other nodes, I need to determine the number of hops between this machine and the node I'm wishing to connect to.
I have looked around a lot for this information, but to no avail.... Does anyone know if there is an already in place API for this? And if not, how I would be able to create my own....
I know this question is pretty old, but I have extensive experience in this field.
What you need is an ad hoc routing protocol, often called MANET (Mobile Adhoc NETwork) protocol. I would suggest that you take a look at OLSR, which is standardized by the IETF as RFC 7181 and RFC 3636.
You can obtain source code and binaries for OLSR at http://www.olsr.org/?q=download.
By using this, OLSR will create routes between all nodes in the network, and by looking at the routing table you will be able to determine the IP address of every node in the network, and can then easily open a socket connection (UDP/TCP) to any of them. You will also get information about the quality of each link, if needed.
Lets say that I have a function todo() and I want to implement this function on a packet sent from a node to a destination among all the routers.
So I want that the packet goes through TCP via ethernet(could be anything) and while going I want to process the packet by calling todo() on it.
I am trying to simulate this on omnet and thus wanted advice on it...
Do i need to implement the entire TCP stack first or is there an inbuilt feature for simulation in it and if there is does it allow me to do the thing I mentioned ??
I am a beginner in using omnet so please provide me with guidelines on how to do this.... Thanks a lot ...
Your question is little confusing.
Routers process IP packets. They dont care about the payload, which might contain a TCP segment.
You have a scenario like this:
Client -> Router -> Server
So the Client will create on L7 a packet and gives it to TCP module. There you can add your function. For example in the sendToIP function
The packet goes to IP and goes out via Ethernet to the Router. Router looks at destination IP address and send it out the interface as configured in routing table.
The server will receive the packet. it goes through its tcp module (their you can also add your todo() function) and gives it to your application module.
Is there an existing Linux/POSIX C/C++ library or example code for how to rebind a socket from one physical interface to another?
For example, I have ping transmitting on a socket that is associated with a physical connection A and I want to rebind that socket to physical connection B and have the ping packets continue being sent and received on connection B (after a short delay during switch-over).
I only need this for session-less protocols.
Thank you
Update:
I am trying to provide failover solution for use with PPP and Ethernet devices.
I have a basic script which can accomplish 90% of the functionality through use of iptables, NAT and routing table.
The problem is when the failover occurs, the pings continue being sent on the secondary connection, however, their source IP is from the old connection.
I've spoken with a couple of people who work on commercial routers and their suggestion is to rebind the socket to the secondary interface.
Update 2:
I apologise for not specifying this earlier. This solution will run on a router. I cannot change the ping program because it will run on the clients computer. I used ping as just an example, any connection that is not session-based should be capable of being switched over. I tested this feature on several commercial routers and it does work. Unfortunately, their software is proprietary, however, from various conversations and testing, I found that they are re-binding the sockets on failover.
As of your updated post, the problem is that changing the routing info is not going to change the source address of your ping, it will just force it out the second interface. This answer contains some relevant info.
You'll need to change the ping program. You can use a socket-per-interface approach and somehow inform the program when to fail over. Or you will have to close the socket and then bind to the second interface.
You can get the interface info required a couple of ways including calling ioctl() with the SIOCGIFCONF option and looping through the returned structures to get the interface address info.
I do't think that's quite a well-defined operation. the physical interfaces have different MAC addresses, so unless you have a routing layer mapping them (NAT or the like) then they're going to have different IP addresses.
Ports are identified by a triple of <IP addr, Port number, protocol> so if your IP address changes the port is going to change.
What are you really trying to do here?
I'm not at all sure what you're trying to accomplish, but I have a guess... Are you trying to do some kind of failover? If so, then there are indeed ways to accomplish that, but why not do it in the OS instead of the application?
On one end you can use CARP, and on the other you can use interface trunking/bonding (terminology varies) in failover mode.