On 11/21/2013 09:06 AM, James Hogarth wrote:
>
>
>
> On 20 November 2013 22:29, Louis Lagendijk <louis(a)fazant.net
<mailto:louis@fazant.net>> wrote:
>
> On Wed, 2013-11-20 at 16:21 -0600, Kevin Martin wrote:
> > On 11/20/2013 03:21 PM, Louis Lagendijk wrote:
> > > Some time ago I asked a question about the broadcast address on
Fedora
> > > 20. On my desktop (installed from one of Alpha TC's) the interface
is
> > > brought up correctly, except that the broadcast address does not get
set
> > > correctly:
> > > Ifconfig reports:
> > >
> > >> p5p1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
> > >> inet 192.168.159.186 netmask 255.255.255.0 broadcast
0.0.0.0
> > >> inet6 2001:981:688d:f2:1e6f:65ff:fed5:7742 prefixlen 128
> > >> scopeid 0x0<global>
> > >> inet6 fe80::1e6f:65ff:fed5:7742 prefixlen 64 scopeid
> > >> 0x20<link>
> > >> ether 1c:6f:65:d5:77:42 txqueuelen 1000 (Ethernet)
> > >> RX packets 568712 bytes 540500284 (515.4 MiB)
> > >> RX errors 0 dropped 0 overruns 0 frame 0
> > >> TX packets 359977 bytes 282238000 (269.1 MiB)
> > >> TX errors 0 dropped 0 overruns 0 carrier 0 collisions
0
> > >
> > > The broadcast address is not set when I use DHCP, but is also missing
> > > when I use static address allocation. When I try a
> > > ifdown p5p1; ifup05p1
> > > the broadcast address is setup correctly.
> > >
>
>
> Interestingly enough using the iproute tools mirrors the net-tools here to some
extent... although net-tools reports 0.0.0.0 whereas
> iproute shows no broadcast address:
>
> 2: p4p1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group
default qlen 1000
> link/ether d4:be:d9:7e:f3:ce brd ff:ff:ff:ff:ff:ff
> inet 10.81.10.110/24 <
http://10.81.10.110/24> scope global dynamic p4p1
> valid_lft 18508sec preferred_lft 18508sec
> inet6 fe80::d6be:d9ff:fe7e:f3ce/64 scope link
> valid_lft forever preferred_lft forever
>
> No brd bit is included in this compared to another interface that does have it:
>
> 12: virbr1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
group default
> link/ether 52:54:00:72:fa:28 brd ff:ff:ff:ff:ff:ff
> inet 192.168.244.1/24 <
http://192.168.244.1/24> brd 192.168.244.255 scope
global virbr1
> valid_lft forever preferred_lft forever
>
> However I'm curious as to the consequences of this given that broadcast address
is just a function of network address against
> network mask anyway ...
>
>
>
>
I'm guessing (and this is only a guess) that most network tools don't derive
broadcast address "on the fly" but use the system
settings when the broadcast address information is needed. It becomes of particular
importance I would suppose when using a mask
that could be considered atypical (whatever that might be). I just find it disturbing
that this has suddenly stopped being set by
default (for example,the network scripts, when not using NetworkManager, use ipcalc to
set the broadcast address (which is why ifup
sets the address correctly) but dhclient/NetworkManager apparently are ignoring this at
this time). I've yet to find anything on
the web that indicates that this was a conscious decision.
For applications it is
often ok to use the global broadcast
(255.255.255.255). In a multi-homed setup that can become tricky so then
it is better to use the network broadcast address. I have therefore
raised a bugzilla case (BZ 1032819) for this. I am not sure whether this
qualifies as a blocker (networking is blocking, but this is not
completely so I doubt if it should qualify) but it is awkward in certain
cases. As the ifdown/ ifup case sets the broadcast I am fairly confident
that thi is a bug somewhere (mot likely NM) but I unfortunately don't
know how to debug this. The old network script was much easier to debug
Br, Louis