doc/README.link-local

   1 ------------------------------------------
   2  Link-local IP address auto-configuration
   3 ------------------------------------------
   4
   5 Negotiate with other link-local clients on the local network
   6 for an address that doesn't require explicit configuration.
   7 This is especially useful if a DHCP server cannot be guaranteed
   8 to exist in all environments that the device must operate.
   9
  10 This is an implementation of RFC3927.
  11
  12 ----------
  13  Commands
  14 ----------
  15
  16 When CONFIG_CMD_LINK_LOCAL is defined in the board config file,
  17 the "linklocal" command is available.  This running this will
  18 take approximately 5 seconds while the address is negotiated.
  19
  20 ------------------------
  21  Environment interation
  22 ------------------------
  23
  24 The "llipaddr" variable is set with the most recently
  25 negotiated address and is preferred in future negotiations.
  26
  27 The "ipaddr", "netmask", and "gatewayip" variables are set
  28 after successful negotiation to enable network access.
  29
  30 -------------
  31  Limitations
  32 -------------
  33
  34 RFC3927 requires that addresses are continuously checked to
  35 avoid conflicts, however this can only happen when the NetLoop
  36 is getting called.  It is possible for a conflict to go undetected
  37 until a command that accesses the network is executed.
  38
  39 Using NetConsole is one way to ensure that NetLoop is always
  40 processing packets and monitoring for conflicts.
  41
  42 This is also not a concern if the feature is use to connect
  43 directly to another machine that may not be running a DHCP server.
  44
  45 ----------------
  46  Example script
  47 ----------------
  48
  49 This script allows use of DHCP and/or Link-local controlled
  50 by env variables.  It depends on CONFIG_CMD_LINK_LOCAL, CONFIG_CMD_DHCP,
  51 and CONFIG_BOOTP_MAY_FAIL.
  52 If both fail or are disabled, static settings are used.
  53
  54 #define CONFIG_EXTRA_ENV_SETTINGS \
  55         "ipconfigcmd=if test \\\"$dhcpenabled\\\" -ne 0;"               \
  56                 "then "                                                 \
  57                         "dhcpfail=0;dhcp || dhcpfail=1;"                \
  58                 "else "                                                 \
  59                         "dhcpfail=-1;"                                  \
  60                 "fi;"                                                   \
  61                 "if test \\\"$linklocalenabled\\\" -ne 0 -a "           \
  62                         "\\\"$dhcpfail\\\" -ne 0;"                      \
  63                 "then "                                                 \
  64                         "linklocal;"                                    \
  65                         "llfail=0;"                                     \
  66                 "else "                                                 \
  67                         "llfail=-1;"                                    \
  68                 "fi;"                                                   \
  69                 "if test \\\"$llfail\\\" -ne 0 -a "                     \
  70                         "\\\"$dhcpfail\\\" -ne 0; "                     \
  71                 "then "                                                 \
  72                         "setenv ipaddr $sipaddr; "                      \
  73                         "setenv netmask $snetmask; "                    \
  74                         "setenv gatewayip $sgatewayip; "                \
  75                 "fi;\0"                                                 \