Trying to ping from a subinterface.

[CLOSE Dave]

On Fedora 20 x86_64.

According to "man ping", ping should work from a subinterface specifying 
either the interface name or its address:
> -I interface
>    interface is either an address, or an interface name.  If inter‐
>    face is an address, it sets source address to  specified  inter‐
>    face address.  If interface in an interface name, it sets source
>    interface to specified interface.

I've got a subinterface and I'm trying to ping from it.
> # ifconfig eth3:sub1
> eth3:sub1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
>        inet 172.17.30.143  netmask 255.255.254.0  broadcast 172.17.31.255
>        ether 90:e2:ba:34:46:41  txqueuelen 1000  (Ethernet)
>        device memory 0xdc7e0000-dc800000

If I ping from the address, it works as specified. If I specify the 
interface name instead, I see:
> # ping -I eth3:sub1 172.17.30.1
> ping: SO_BINDTODEVICE: Invalid argument

Investigating a little deeper:
> # strace ping -I eth3:sub1 172.17.30.1
> execve("/usr/bin/ping", ["ping", "-I", "eth3:sub1", "172.17.30.1"], [/* 38 vars */]) = 0
> ...
> setsockopt(4, SOL_SOCKET, SO_BINDTODEVICE, "eth3:sub1\0", 13) = -1 ENODEV (No such device)
> ...
> +++ exited with 2 +++

Any thoughts?

[Rick Stevens]

On 06/02/2014 11:18 AM, CLOSE Dave issued this missive:
> On Fedora 20 x86_64.
>
> According to "man ping", ping should work from a subinterface specifying
> either the interface name or its address:
> > -I interface
> >     interface is either an address, or an interface name.  If inter‐
> >     face is an address, it sets source address to  specified  inter‐
> >     face address.  If interface in an interface name, it sets source
> >     interface to specified interface.
>
> I've got a subinterface and I'm trying to ping from it.
> > # ifconfig eth3:sub1
> > eth3:sub1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
> >         inet 172.17.30.143  netmask 255.255.254.0  broadcast 172.17.31.255
> >         ether 90:e2:ba:34:46:41  txqueuelen 1000  (Ethernet)
> >         device memory 0xdc7e0000-dc800000
>
> If I ping from the address, it works as specified. If I specify the
> interface name instead, I see:
> > # ping -I eth3:sub1 172.17.30.1
> > ping: SO_BINDTODEVICE: Invalid argument
>
> Investigating a little deeper:
> > # strace ping -I eth3:sub1 172.17.30.1
> > execve("/usr/bin/ping", ["ping", "-I", "eth3:sub1", "172.17.30.1"], [/* 38 vars */]) = 0
> > ...
> > setsockopt(4, SOL_SOCKET, SO_BINDTODEVICE, "eth3:sub1\0", 13) = -1 ENODEV (No such device)
> > ...
> > +++ exited with 2 +++
>
> Any thoughts?

"eth3:sub1" isn't an interface, it's an alias. The interface name is
the bit before the ":" (or "." in the case of a VLAN).

If you were to do a "netstat -rn", you'd only see "eth3" as a network
device. You wouldn't see "eth3:sub1" listed.
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[CLOSE Dave]

I wrote:
> # ping -I eth3:sub1 172.17.30.1
> ping: SO_BINDTODEVICE: Invalid argument

Rick Stevens responded:
> "eth3:sub1" isn't an interface, it's an alias. The interface name is
> the bit before the ":" (or "." in the case of a VLAN).
>
> If you were to do a "netstat -rn", you'd only see "eth3" as a network
> device. You wouldn't see "eth3:sub1" listed.

Thanks. And you are obviously correct, technically. But this command 
worked as I expected on earlier versions of Fedora. We now have many 
procedures with such commands embedded and were surprised to discover 
they no longer work on F20. Why was it changed?

[CLOSE Dave]

I wrote:
> Thanks. And you are obviously correct, technically. But this command
> worked as I expected on earlier versions of Fedora. We now have many
> procedures with such commands embedded and were surprised to discover
> they no longer work on F20. Why was it changed?

I take it back. I was led to believe things were working in the past. In 
fact, the difference is that F20 refuses to do the ping whereas earlier 
versions complained and then fell back to pinging from the interface 
address.

F20: # ping -I eth3:sub1 172.17.30.1
      ping: SO_BINDTODEVICE: Invalid argument

F14: # ping -I eth3:sub1 172.17.30.1
      Warning: cannot bind to specified iface, falling back: No such device
      PING 172.17.30.1 (172.17.30.1) from 172.17.30.161 eth3:sub1:
      64 bytes from ...

Sorry for the confusion.