Trying to ping from a subinterface.

[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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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
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