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Nikolay Denev

2010-Oct-17 14:37 UTC

ifconfig, vnets and interface names

Hello,

While playing with vnet jails I've discovered the following oddity, which
probably is not what's expected to happen :


First I'm creating two epair(4) interfaces :

    [16:51]root@nas:/home/ndenev# ifconfig epair0 create
    epair0a
    [16:51]root@nas:/home/ndenev# ifconfig epair1 create
    epair1a

Then I'm creating two vnet jails :

    [16:51]root@nas:/home/ndenev# jail -c vnet name=test1 host.hostname=test1
path=/ persist
    [16:51]root@nas:/home/ndenev# jail -c vnet name=test2 host.hostname=test2
path=/ persist

Now push one side of the epairs to each vnet :

    [16:51]root@nas:/home/ndenev# ifconfig epair0b vnet test1
    [16:52]root@nas:/home/ndenev# ifconfig epair1b vnet test2

Rename the interfaces in the vnet jails :

    [16:52]root@nas:/home/ndenev# jexec test1 ifconfig epair0b name eth0
    [16:52]root@nas:/home/ndenev# jexec test2 ifconfig epair1b name eth0

And now I'm destroying the vnets, so all of the interfaces are
"reclaimed" by the host :

    [16:52]root@nas:/home/ndenev# jail -r test1
    [16:52]root@nas:/home/ndenev# jail -r test2

And that's what ifconfig shows after this :

    [16:52]root@nas:/home/ndenev# ifconfig     
    <... snip lo0 and physical interface ...>
    epair0a: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
	    ether 02:8c:53:00:03:0a
    epair1a: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
	   ether 02:b6:49:00:05:0a
    eth0: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
	    ether 02:8c:53:00:04:0b
	    ether 02:b6:49:00:06:0b

Instead of two interfaces, I'm seeing one with to lladdrs, because of the
interface names being the same.

Then I'm trying to destroy them :

    [16:52]root@nas:/home/ndenev# ifconfig eth0 destroy
    [16:53]root@nas:/home/ndenev# ifconfig 
    <... snip lo0 and physical interface ...>
    epair1a: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
	    ether 02:b6:49:00:05:0a
    eth0: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
	    ether 02:b6:49:00:06:0b
    [16:53]root@nas:/home/ndenev# ifconfig eth0 destroy


So in this case there may be not a clean way to address one of the interfaces
specifically (i.e. destroy only the second one)?

I've not investigated further, but I'm thinking probably this is just a
"bug" in ifconfig interpreting/parsing the information from the
kernel.
Maybe a solution is to extend ifconfig to be able print the interface list along
with the ifIndex values and also manage the interfaces by index?
Auto renaming also is also probably a possible solution (i.e. eth0_1 , eth0_2 )
as these are interfaces coming from destroyed vnet's and are not likely to
be in use. (but still sounds scary :) )

Regards,
Nikolay

Bjoern A. Zeeb

2010-Oct-17 16:20 UTC

head link

ifconfig, vnets and interface names

On Sun, 17 Oct 2010, Nikolay Denev wrote:
> Hello,
>
> While playing with vnet jails I've discovered the following oddity,
which probably is not what's expected to happen :
>
...> And that's what ifconfig shows after this :
>
>    [16:52]root@nas:/home/ndenev# ifconfig
>    <... snip lo0 and physical interface ...>
>    epair0a: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0
mtu 1500
> 	    ether 02:8c:53:00:03:0a
>    epair1a: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0
mtu 1500
> 	   ether 02:b6:49:00:05:0a
>    eth0: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
> 	    ether 02:8c:53:00:04:0b
> 	    ether 02:b6:49:00:06:0b
>
> Instead of two interfaces, I'm seeing one with to lladdrs, because of
the interface names being the same.
>
> Then I'm trying to destroy them :
>
>    [16:52]root@nas:/home/ndenev# ifconfig eth0 destroy
>    [16:53]root@nas:/home/ndenev# ifconfig
>    <... snip lo0 and physical interface ...>
>    epair1a: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0
mtu 1500
> 	    ether 02:b6:49:00:05:0a
>    eth0: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
> 	    ether 02:b6:49:00:06:0b
>    [16:53]root@nas:/home/ndenev# ifconfig eth0 destroy
>
>
> So in this case there may be not a clean way to address one of the
interfaces specifically (i.e. destroy only the second one)?
>
> I've not investigated further, but I'm thinking probably this is
just a "bug" in ifconfig interpreting/parsing the information from the
kernel.
> Maybe a solution is to extend ifconfig to be able print the interface list
along with the ifIndex values and also manage the interfaces by index?
> Auto renaming also is also probably a possible solution (i.e. eth0_1 ,
eth0_2 ) as these are interfaces coming from destroyed vnet's and are not
likely to be in use. (but still sounds scary :) )
It's actually a bug in sys/net/if.c:if_vmove* we know about and that's
on the todo list.

I am not sure when the behaviour of ifconfig changed as previousy it
would only show you one of the two interfaces with the single ether
address.  ifconfig -l however had shown eth0 twice.  Neither is really
what one would expect thus needs changing.

/bz

PS: freebsd-virtualization@ is the best list to report "VIMAGE" or
"vnet" related problems.

-- 
Bjoern A. Zeeb                              Welcome a new stage of life.

freebsd stable - Oct 2010 - ifconfig, vnets and interface names

ifconfig, vnets and interface names

ifconfig, vnets and interface names