linux/Documentation/networking/alias.txt
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   2IP-Aliasing:
   3============
   4
   5IP-aliases are an obsolete way to manage multiple IP-addresses/masks
   6per interface. Newer tools such as iproute2 support multiple
   7address/prefixes per interface, but aliases are still supported
   8for backwards compatibility.
   9
  10An alias is formed by adding a colon and a string when running ifconfig.
  11This string is usually numeric, but this is not a must.
  12
  13o Alias creation.
  14  Alias creation is done by 'magic' interface naming: eg. to create a
  15  200.1.1.1 alias for eth0 ...
  16  
  17    # ifconfig eth0:0 200.1.1.1  etc,etc....
  18                   ~~ -> request alias #0 creation (if not yet exists) for eth0
  19
  20    The corresponding route is also set up by this command. 
  21    Please note: The route always points to the base interface.
  22        
  23
  24o Alias deletion.
  25  The alias is removed by shutting the alias down:
  26
  27    # ifconfig eth0:0 down
  28                 ~~~~~~~~~~ -> will delete alias
  29
  30                                   
  31o Alias (re-)configuring
  32
  33  Aliases are not real devices, but programs should be able to configure and
  34  refer to them as usual (ifconfig, route, etc).
  35
  36
  37o Relationship with main device
  38
  39  If the base device is shut down the added aliases will be deleted 
  40  too.
  41
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