Incorrect network mask and broadcast address on Linux when there are multiple IPv4 addresses on an interface

Details copied from descriptions posted to net-dev, see...
  http://mail.openjdk.java.net/pipermail/net-dev/2014-December/008806.html
  http://mail.openjdk.java.net/pipermail/net-dev/2015-January/008829.html

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Incorrect network mask and broadcast address on Linux when there are multiple IPv4 addresses on an interface

Output from ip addr command on the linux box:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
     inet 127.0.0.1/8 scope host lo
     inet6 ::1/128 scope host
        valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
state UP qlen 1000
     link/ether 08:00:27:fc:25:9f brd ff:ff:ff:ff:ff:ff
     inet 192.168.1.4/24 brd 192.168.1.255 scope global eth0
     inet6 fe80::a00:27ff:fefc:259f/64 scope link
        valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
state UP qlen 1000
     link/ether 08:00:27:b1:42:d0 brd ff:ff:ff:ff:ff:ff
     inet 192.168.240.1/24 brd 192.168.240.255 scope global eth1
     inet 192.168.241.1/24 brd 192.168.241.255 scope global eth1
     inet 192.168.239.1/24 brd 192.168.239.255 scope global eth1
     inet 10.0.0.1/22 brd 10.0.3.255 scope global eth1
     inet6 fe80::a00:27ff:feb1:42d0/64 scope link
        valid_lft forever preferred_lft forever

And this is the output of a test java program that uses
NetworkInterfaces class to display all IP addresses and their
corresponding settings:

eth1:10.0.0.1/24 broadcast:192.168.240.255
eth1:192.168.239.1/24 broadcast:192.168.240.255
eth1:192.168.241.1/24 broadcast:192.168.240.255
eth1:192.168.240.1/24 broadcast:192.168.240.255
eth0:192.168.1.4/24 broadcast:192.168.1.255
lo:127.0.0.1/8

There are 2 problems visible here:

1. On all eth1 lines same broadcast is displayed. The value is the
broadcast of the first IP address set on that interface

2. All addresses are with prefix length of 24 which is not correct. We
have 10.0.0.1/22 in the "ip addr" output.

So the problem is in NetworkInterfaces native code for Unix.

For IPv4 addresses that code uses 2 functions (getBordacast and
getSubnet and these 2 functions use ioctl with SIOCGIFNETMASK and
SIOCGIFBRDADDR. Both of these requests receive as parameter interface
name. They are not prepared to work in environments where you can
specify more then one IP on the same interface without using virtual
interfaces.

So using virutal interfaces is the only workaround of this problem for
the moment.

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In order to setup dummy interface with test values you can use these
commands:

ip link add dummy0 type dummy

ip addr add 10.5.5.1/28 brd 10.5.5.15 dev dummy0
ip addr add 10.6.0.1/23 brd 10.6.1.255 dev dummy0
ip addr add 10.7.0.1/25 brd 10.7.0.127 dev dummy0

The output from NetworkInterface test
test/java/net/NetworkInterface/NetParamsTest.java for this interface is:

dummy0 :
    Status: DOWN
    Hardware Address: 56:ffffffd4:fffffffd:ffffffc2:ffffffec:ffffff82:
    Loopback: false
    Point to Point: false
    Virtual: false
    Multicast: false
    MTU: 1500
    Bindings:
        /10.7.0.1/25 [/10.7.0.127]
        /10.6.0.1/23 [/10.6.1.255]
        /10.5.5.1/28 [/10.5.5.15]

This is the output from Java 1.8.0_25. Same output is produced with
existing version of NetworkInterface.c in JDK 9

dummy0 :
    Status: DOWN
    Hardware Address: 56:ffffffd4:fffffffd:ffffffc2:ffffffec:ffffff82:
    Loopback: false
    Point to Point: false
    Virtual: false
    Multicast: false
    MTU: 1500
    Bindings:
        /10.7.0.1/28 [/10.5.5.15]
        /10.6.0.1/28 [/10.5.5.15]
        /10.5.5.1/28 [/10.5.5.15]