How to bind sockets to a virtual interface?

Question

In the setup I'm working with I have multiple interfaces and some of them have exact same IPs. i.e: ifconfig returns

eno1: ... inet 192.168.2.1  netmask 255.255.255.0 ...
eno2: ... inet 192.168.2.1  netmask 255.255.255.0 ...

Yes, I know it's crazy but unfortunately I can not change the IPs. So when I am binding the sockets, in this specific case they are UDP sockets to receive data, I have to bind the socket to the interface with something like this:

// if interface is provided, bind to the interface
if (szIfr != 0)
{
    struct ifreq ifr;
    memset(&ifr, 0, sizeof(ifr));
    snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), szIfr);
    if (setsockopt(m_sSocket, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0)
    {
        printf("OPEN(): error binding to %s. Error returned: %s\n", szIfr, strerror(errno));
        return CUDP_BIND;
    }
}

and it works perfectly. But I'm having problem with binding the socket with a virtual interface. This is my actual setup

...
eno1:   ... inet 192.168.2.1    netmask 255.255.255.0 ...
eno1:0: ... inet 10.24.6.1      netmask 255.255.255.0 ...
eno1:1: ... inet 10.8.6.4       netmask 255.255.255.0 ...
eno2:   ... inet 192.168.2.1    netmask 255.255.255.0 ...
...

So, when I try to bind to eno1:0 I get this error: No such device and it also makes sense. Because the interface is virtual and it doesn't exist. But If I try to bind to the real interface eno1 with the IP of the virtual interface I don't receive any packet on that socket. If I just bind it to the IP without specifying the name of the interface I don't get any error but I still don't receive the data.

What am I doing wrong here? Is it something to do with the interface settings or I have to modify my code?

I'm testing this code on RedHat 7.1 with kernel redhat kernel 4.1.5.

Stian Skjelstad Stian Skjelstad · Accepted Answer · 2016-04-22T10:25:34

eno1:0 is not virtual interface, it is just an alias for eno1. Binding to eno1 with IP 0.0.0.0 (INADDR_ANY) should work for the virtual interfaces aswell. A bigger problem when you have the same network address on multiple devices is the routing table, that is used to decide which interface to use when sending data

How to bind sockets to a virtual interface?

1 Answers