Debian Bug report logs - #186208
the calculated broadcast address is wrong when subnetting

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: Arndt Schoenewald <arndt@lin02384n012.mc.schoenewald.de>

To: submit@bugs.debian.org

Subject: the calculated broadcast address is wrong when subnetting

Date: Tue, 25 Mar 2003 10:44:31 +0100

Package: ifupdown
Version: 0.6.4-4.4

The interfaces(5) man page indicates that the "broadcast" parameter is
optional for static interface configurations, but if it is not given,
a wrong value is calculated when subnetting is used.

Example:
    iface eth2 inet static
	address 10.0.0.42
	netmask 255.255.255.240

When eth2 is brought up (kernel 2.4.21pre5, net-tools 1.60-4), its
configuration looks like this:

    eth2  Link encap:Ethernet  HWaddr 00:E0:03:08:46:6D  
          inet addr:10.0.0.42  Bcast:10.255.255.255  Mask:255.255.255.240
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

i.e. the broadcast address is 10.255.255.255 but should be 10.0.0.47.

As you know, the formula for calculating the broadcast address is

    (address & netmask) | !netmask

You could argue that the problem is with ifconfig (ifconfig sets the
wrong broadcast address if none is specified), but then again why doesn't
ifup call it with a valid broadcast address? (And if you argue that way,
why do you require that the netmask be given? ifconfig does not require
this parameter.) I don't think that, on Debian, people should have to
know about the peculiarities of ifconfig since the published mechanism
for defining network interfaces is the ifupdown system. And giving an
address together with a netmask is nowadays the common way.

If you still think this should stay as it is, at least add a note to
interfaces(5) that the broadcast parameter is needed, too.

Thank you very much,
Arndt

-- 
Arndt Schönewald <arndt@lin02384n012.mc.schoenewald.de>, Software Developer
Quelltext AG (http://www.quelltext-ag.de), Dortmund, Germany

Message #14 received at 186208@bugs.debian.org (full text, mbox, reply):

From: Martín Ferrari <tincho@debian.org>

To: 186208@bugs.debian.org

Subject: Closing old bug

Date: Mon, 16 Mar 2009 01:49:26 -0300

Package: net-tools
Version: 1.60-17

Following #87784, #122792 and #145004 (boy, this one had many
duplicates), I'm closing this bug because it's not reproducible even on
etch systems, I can reproduce it on sarge, though.

On Sarge:

# ifconfig dummy0 128.42.162.116 netmask 255.255.255.0
# ifconfig dummy0 | head -n2
dummy0    Link encap:Ethernet  HWaddr C2:C5:EF:F4:92:1A  
          inet addr:128.42.162.116  Bcast:128.42.255.255
Mask:255.255.255.0
# dpkg -s net-tools | grep ^Version:
Version: 1.60-10

On Etch and newer systems:

# ifconfig dummy0 128.42.162.116 netmask 255.255.255.0
# ifconfig dummy0 | head -n2
dummy0    Link encap:Ethernet  HWaddr 3A:B1:38:29:F1:FE  
          inet addr:128.42.162.116  Bcast:128.42.162.255
Mask:255.255.255.0
# dpkg -s net-tools | grep ^Version:
Version: 1.60-17

Message #19 received at 186208-done@bugs.debian.org (full text, mbox, reply):

From: Martín Ferrari <tincho@debian.org>

To: 186208-done@bugs.debian.org

Subject: Fwd: Bug#186208: Closing old bug

Date: Mon, 16 Mar 2009 01:57:37 -0300

Package: net-tools
Version: 1.60-17

Following #87784, #122792 and #145004 (boy, this one had many
duplicates), I'm closing this bug because it's not reproducible even on
etch systems, I can reproduce it on sarge, though.

On Sarge:

# ifconfig dummy0 128.42.162.116 netmask 255.255.255.0
# ifconfig dummy0 | head -n2
dummy0    Link encap:Ethernet  HWaddr C2:C5:EF:F4:92:1A
         inet addr:128.42.162.116  Bcast:128.42.255.255
Mask:255.255.255.0
# dpkg -s net-tools | grep ^Version:
Version: 1.60-10

On Etch and newer systems:

# ifconfig dummy0 128.42.162.116 netmask 255.255.255.0
# ifconfig dummy0 | head -n2
dummy0    Link encap:Ethernet  HWaddr 3A:B1:38:29:F1:FE
         inet addr:128.42.162.116  Bcast:128.42.162.255
Mask:255.255.255.0
# dpkg -s net-tools | grep ^Version:
Version: 1.60-17








-- 
Martín Ferrari

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