Unable to understand ifup/ifdown proceedings

Question

I am trying to setup virtual ip for ucarp. But after configuration something strange happens with ifup ifdown as try to view the configurations. I change /etc/network/interfaces like

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

# The primary network interface
auto enp0s3
iface enp0s3 inet static
address 10.1.178.153
netmask 255.255.255.0
gateway 10.1.178.1
dns-nameservers 10.1.171.200

  #######################
  # ucarp configuration
  #######################
  # vid : The ID of the virtual server [1-255]
  ucarp-vid 1
  # vip : The virtual address
  ucarp-vip 10.1.178.150
  # password : A password used to encrypt Carp communications
  ucarp-password secret
  # advskew : Advertisement skew [1-255]
  ucarp-advskew 100
  # advbase : Interval in seconds that advertisements will occur
  ucarp-advbase 1
  # master : determine if this server is the master

# The carp network interface, on top of enp0s3
iface enp0s3:ucarp inet static
        address 10.1.178.150
        netmask 255.255.255.0
        gateway 10.1.178.1
        dns-nameservers 10.1.171.200

Below is the output from terminal proceedings after that

$ sudo service networking restart
$ ifconfig
enp0s3    Link encap:Ethernet  HWaddr 08:00:27:c6:9b:54  
          inet addr:10.1.178.153  Bcast:10.1.178.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fec6:9b54/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2826136 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1271544 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:320630219 (320.6 MB)  TX bytes:94783376 (94.7 MB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:37307 errors:0 dropped:0 overruns:0 frame:0
          TX packets:37307 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:3039725 (3.0 MB)  TX bytes:3039725 (3.0 MB)

I try to take enp0s3 down so that enp0s3:ucarp can be taken up, but there is a surprise#1

$ sudo ifdown enp0s3
RTNETLINK answers: No such process
$ ifconfig
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:37358 errors:0 dropped:0 overruns:0 frame:0
          TX packets:37358 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:3042933 (3.0 MB)  TX bytes:3042933 (3.0 MB)

Okay, now that enp0s3 does not show up I try to bring enp0s3:ucarp up. But here comes surprise#2

$ sudo ifup enp0s3:ucarp
RTNETLINK answers: File exists
run-parts: /etc/network/if-up.d/avahi-autoipd exited with return code 2
Failed to bring up enp0s3:ucarp.
$ ifconfig
enp0s3    Link encap:Ethernet  HWaddr 08:00:27:c6:9b:54  
          inet6 addr: fe80::a00:27ff:fec6:9b54/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2826298 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1271688 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:320646091 (320.6 MB)  TX bytes:94802033 (94.8 MB)

enp0s3:ucarp Link encap:Ethernet  HWaddr 08:00:27:c6:9b:54  
          inet addr:10.1.178.150  Bcast:10.1.178.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:37376 errors:0 dropped:0 overruns:0 frame:0
          TX packets:37376 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:3044101 (3.0 MB)  TX bytes:3044101 (3.0 MB)

Not able to understand; not able to configure ucarp; Request someone to help get me some inner-peace with this !!

• Does ifconfig display active network configuration/all network configuration regardless of up/down ?
• How is making a virtual adress up resulting in primary interface being up as well ?

Answer 1

Nevermind, an update to Ubuntu 15.10 seems to have solved the problem. Additionally, learnt to cross-verify every operation against /run/network/ifstate as well.