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 <b...@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 <b...@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 > > > _______________________________________________ > > dev mailing list > > d...@openvswitch.org > > https://mail.openvswitch.org/mailman/listinfo/ovs-dev > > _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev