I am trying to connect over Linux. My device is connected to two LANs (say eth0 and eth1) with different networks.
Both networks are connected to internet. I want my client program to be able to use eth1 even though my eth0 is the default interface.
There is an option setsockopt (SO_BINDTODEVICE) to bind to a specific interface but requires root priviledges which is not possible.
Binding to IP address of eth1 is not helping either. Please suggest is there any other way through socket APIs to link the connection with the interface. i.e. my client program will always usse eth1 source IP and interface to connect to the internet whereas all other programs will continue to use eth0 as ususal.
I investigated and appears changes in routing table can help in this but trying to avoid being risky to make system unstable as that is applied to every other programs too.
Thanks in advance.
Kris
Related
Is it possible to connect the Ethernet port (of a Raspberry Pi) directly to a Modbus TCP RJ45 port (such that the devices can talk to each other)? Or is this not possible without a converter?
I am unsure if this is the correct forum, but I believe this should not be specific to the Raspberry pi.
Short answer - Yes... But....
As per the comments this is possible but there are a few things you will need to do (i.e. some configuration will be needed).
I think it's worth nothing that "Modbus TCP RJ45 port" is not really a meaningful term. Modbus is an application layer protocol; this depends upon a number of underlying layers:
Transport layer - TCP
Network layer - IP
Datalink Layer - Ethernet
Physical Layer - Ethernet cable with RJ45 connectors
You don't need to understand this in detail; the point is that before ModbusTCP will work you need to have a working TCP network (which all Modbus-TCP devices will support; generally via an RJ45 Ethernet connection). As such a better question probably is "If I run a CAT-5 cable between a Raspberry Pi and another device (Modbus TCP unit) will I be able to connect via TCP?" (a lot more people know about TCP/IP networking than Modbus!).
The first thing to consider is Ethernet. Running a cable directly between two older devices will often not work because they needed a crossover cable. Almost all modern equipment (including the Pi) supports Auto MDI-X which means the cable will just work. You can also connect the units via a switch (and doing this removes the need for Auto MDI-X).
Next you need to consider the IP layer. When you connect your Pi to your home network it will (usually!) be given an IP address by a DHCP service (usually running on your router). If you are connecting the Pi directly to the device then there will be no DHCP service so you will need to manually assign IP addresses to the devices (and ensure the subnet is correctly configured). A common way to check if an IP connection is working is to use the ping command.
With the lower layers working ModbusTCP will generally 'just work'. Many ModbusTCP devices also offer a browser based configuration and checking that you can access that is a good way to confirm that the network link is working.
One further question is probably "should I do this"; it's OK to hook things up this way to make some quick changes. However generally you will want the Pi to access other network resources so connecting everything to a router (home router will work; for remote devices a cell router is often used). You can either give the Modbus unit a static IP manually or use the routers configuration pages to assign it a static DHCP lease (otherwise it's IP might change from time to time).
I need to create a TCP session "manually", without using the connect() function. I have tried to use RAW sockets. But in this case, I only get copies of the incoming IP packets. The original incoming packets slip through to the kernel and it generates an ACK response packet that damages my protocol.
Next, variant 2, I can write a virtual eth interface driver (kernel module) and route incoming traffic to it using iptables. But there is a patched non-original (non vanila) kernel on the machine. Normal linking of the module with the kernel is not possible.
Variant 3. I also tried not to assign an IP address to the NIC interface. In this case, the network TCP/IP layer module in the kernel is not activated and it is possible to generate and receive arbitrary IP packets on the link (ethernet) layer using the PF_PACKET socket domain type in the socket() function. But at this time, any other applications using the TCP/IP protocol can’t work.
How can this problem be solved in other ways?
It would be nice if it were possible to intercept packets going from the network interface to the kernel, that is, intercept the SKBuf buffer. But I don't know how to realize it.
Apparently you are trying to create a tunnel. Instead of trying to hijack an existing interface, the proper way to create a tunnel is to create a new interface, using a kernel module or TUN/TAP. However, tunnels are normally intended to receive traffic generated on the machine which runs the tunnel software, or at least routed through it. That means you will also have to set up the kernel to route the traffic to your tunnel.
You can create a new interface as a TUN/TAP interface. It is like a virtual ethernet driver except you don't need to write a new kernel module. It is designed for tunnels (hence the name).
The difference between TUN and TAP is that a TUN interface is an IP interface that receives IP packets from the kernel's IP routing system, and a TAP interface receives Ethernet packets (which may contain IP packets) so it can alternatively be part of a bridge (a virtual Ethernet switch - which only looks at the Ethernet header, not the IP header).
I think for your scenario, you will find it easiest to create a TAP interface, then create a bridge (virtual Ethernet switch) between the TAP interface, and the interface which the other host is connected to. Neither one needs an IP address - the kernel will happily pass Ethernet-layer traffic without attempting to process the IP information in the packet. Your tunnel software can then emulate a host - or tunnel to an actual host - or whatever you want it to do.
Or in visual form:
If you want the host to also be able to talk to the machine running the tunnel software - without going through the tunnel software - then you may choose to put an IP address on the bridge.
I have a hardware attached to my RPI board running Linux distro. This hardware & its associated Host stack has created a network interface called wpan0 and assigned some IPV6 addresses to it (I am able to ping the IPV6 address from a remote device in the same network)
Now, I want to enable data communication to this interface to any IPV6 IP assigned to the interface. How do I create and bind a socket to this interface? Also, I want to listen to any ports on this interface. How to achieve this?
How you create a socket depends on the language you use (you didn't specify), but when you want to bind a socket to ANY interface the IPv4 way is to listen to IP 0.0.0.0, the IPv6 equivalent is ::/0, that means all zeros/0 bits CIDR mask.
Redirecting all ports to one is less of a code issue and requires some hands on with IPTables and Prerouting (you can write some code that appends that to your conf file though), here is an example:
https://serverfault.com/questions/616535/iptables-destination-ip-and-port
I have a server with a lot of interfaces, and only one interface is assigned IP address, this interface is kept for management.
but other interfaces are connected to the other server.
I want to know which interface is actually connected to the outside server.
Here, I tried to ping to the machine IP with particular interface ping -I eth1 x.x.x.x.
But not able to ping with the interface even though I know this is connected to the server.
All the packet is only going via the management eth0.
Is there a better way to find out which interface is connected to a particular machine?
I know the machine IP address
I am using ubuntu 18.04
I an writing a small application that needs to connect through one of multiple network interfaces on the machine. The interface is not the "default" one (the one with the default route). Is it possible to bind an outbound TCP socket directly to a specific interface?
Here is an example:
eth0: 192.168.1.10, gateway 192.168.1.1
eth1: 192.168.2.10, gateway 192.168.2.1
default gateway: 192.168.1.1
(both interfaces can reach the Internet through different external IPs)
Now, I want my application to use eth1 to connect to an external server, even if the system is configured to use eth0 for external traffic.
(The question is probably trivial, but I just wanted to know if it is possible at all before spending time on it)
Currently, I am using Python with Twisted, but if I have to use BSD sockets then so be it.
From: http://linux.about.com/od/commands/l/blcmdl7_socket.htm
SO_DONTROUTE - Don't send via a gateway, only send to directly connected hosts. The same effect can be achieved by setting the MSG_DONTROUTE flag on a socket send(2) operation. Expects an integer boolean flag.