[ovs-dev] [PATCH v3] Replace most uses of and references to "ifconfig" by "ip".

[Greg Rose]

Top posting...

And then there's this:

https://serverfault.com/questions/460663/is-it-necessary-to-manually-set-the-interface-broadcast-address

- Greg

On Wed, 2017-05-31 at 09:29 -0700, Greg Rose wrote:
> On Wed, 2017-05-31 at 08:32 -0700, Ben Pfaff wrote:
> > On Wed, May 31, 2017 at 11:39:28AM +0200, Matthias May wrote:
> > > On 27/05/17 04:29, Hunt Xu wrote:
> > > > On Fri, May 26, 2017 at 11:46 PM, Ben Pfaff <blp at ovn.org> wrote:
> > > >> It's becoming more common that OSes include "ip" but not "ifconfig", so
> > > >> it's best to avoid using the latter.  This commit removes most references
> > > >> to "ifconfig" and replaces them by "ip".  It also adds a build-time check
> > > >> to make it harder to introduce new uses of "ifconfig".
> > > >>
> > > >> Signed-off-by: Ben Pfaff <blp at ovn.org>
> > > >> ---
> > > > 
> > > > <snip>
> > > > 
> > > >> diff --git a/Documentation/faq/issues.rst b/Documentation/faq/issues.rst
> > > >> index c60336a10569..82d0605da125 100644
> > > >> --- a/Documentation/faq/issues.rst
> > > >> +++ b/Documentation/faq/issues.rst
> > > >> @@ -43,8 +43,8 @@ eth0.  Help!
> > > >>      itself.  For example, assuming that eth0's IP address is 192.168.128.5, you
> > > >>      could run the commands below to fix up the situation::
> > > >>
> > > >> -        $ ifconfig eth0 0.0.0.0
> > > >> -        $ ifconfig br0 192.168.128.5
> > > >> +        $ ip addr flush dev eth0
> > > >> +        $ ip addr add 192.168.128.5 dev br0
> > > > 
> > > > ip addr add 192.168.128.5/24 dev br0
> > > > 
> > > > It seems using ifconfig without specifying any netmask the netmask/prefixlen
> > > > will still be properly set (not diving quite deep, but strace indicates that
> > > > this is not done by ifconfig, ifconfig don't even try to set the netmask),
> > > > whlie using ip-address with only the address specified the prefixlen is
> > > > always 32.
> > > > 
> > > > Some tests on my Ubuntu 16.04:
> > > > 1a. ifconfig br0 192.168.128.5 -> br0 gets 192.168.128.5/24
> > > > 1b. ip addr add 192.168.128.5 dev br0 -> br0 gets 192.168.128.5/32
> > > > 2a. ifconfig br0 172.16.128.5 -> br0 gets 172.16.128.5/16
> > > > 2b. ip addr add 172.16.128.5 dev br0 -> br0 gets 172.16.128.5/32
> > > > 3a. ifconfig br0 10.0.128.5 -> br0 gets 10.0.128.5/8
> > > > 3b. ip addr add 10.0.128.5 dev br0 -> br0 gets 10.0.128.5/32
> > > > 
> > > >>
> > > *snip*
> > > 
> > > You might want to consider to add brd + to the ip command.
> > > E.g. ip addr add 192.168.128.5/24 brd + dev br0
> > > 
> > > Without:
> > > 7: br0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
> > >     link/ether 1a:78:fe:72:9c:be brd ff:ff:ff:ff:ff:ff
> > >     inet 192.168.128.5/24 scope global br0
> > >        valid_lft forever preferred_lft forever
> > > 
> > > With:
> > > 7: br0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
> > >     link/ether 1a:78:fe:72:9c:be brd ff:ff:ff:ff:ff:ff
> > >     inet 192.168.128.5/24 brd 192.168.128.255 scope global br0
> > >        valid_lft forever preferred_lft forever
> > > 
> > > As you can see the broadcast address isn't set without.
> > > 
> > > I see you already posted a v4 but this comment seems more appropriate in this thread.
> > 
> > What happens if no broadcast address is specified?  I've never seen
> > instructions say that one should specify this, so I really wonder
> > whether it is necessary.
> 
> My understanding of this is that the brd command is used to over ride
> the broadcast address that would normally be computed by specifying the
> IP/CIDR.  I don't think it is necessary and I don't generally specify it
> in normal usage.
> 
> Thanks,
> 
> - Greg
> 
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>