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Diffstat (limited to 'doc/README.link-local')
| -rw-r--r-- | doc/README.link-local | 76 |
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diff --git a/doc/README.link-local b/doc/README.link-local new file mode 100644 index 0000000..e623e56 --- /dev/null +++ b/doc/README.link-local @@ -0,0 +1,76 @@ +------------------------------------------ + Link-local IP address auto-configuration +------------------------------------------ + +Negotiate with other link-local clients on the local network +for an address that doesn't require explicit configuration. +This is especially useful if a DHCP server cannot be guaranteed +to exist in all environments that the device must operate. + +This is an implementation of RFC3927. + +---------- + Commands +---------- + +When CONFIG_CMD_LINK_LOCAL is defined in the board config file, +the "linklocal" command is available. This running this will +take approximately 5 seconds while the address is negotiated. + +------------------------ + Environment interation +------------------------ + +The "llipaddr" variable is set with the most recently +negotiated address and is preferred in future negotiations. + +The "ipaddr", "netmask", and "gatewayip" variables are set +after successful negotiation to enable network access. + +------------- + Limitations +------------- + +RFC3927 requires that addresses are continuously checked to +avoid conflicts, however this can only happen when the NetLoop +is getting called. It is possible for a conflict to go undetected +until a command that accesses the network is executed. + +Using NetConsole is one way to ensure that NetLoop is always +processing packets and monitoring for conflicts. + +This is also not a concern if the feature is use to connect +directly to another machine that may not be running a DHCP server. + +---------------- + Example script +---------------- + +This script allows use of DHCP and/or Link-local controlled +by env variables. It depends on CONFIG_CMD_LINK_LOCAL, CONFIG_CMD_DHCP, +and CONFIG_BOOTP_MAY_FAIL. +If both fail or are disabled, static settings are used. + +#define CONFIG_EXTRA_ENV_SETTINGS \ + "ipconfigcmd=if test \\\"$dhcpenabled\\\" -ne 0;" \ + "then " \ + "dhcpfail=0;dhcp || dhcpfail=1;" \ + "else " \ + "dhcpfail=-1;" \ + "fi;" \ + "if test \\\"$linklocalenabled\\\" -ne 0 -a " \ + "\\\"$dhcpfail\\\" -ne 0;" \ + "then " \ + "linklocal;" \ + "llfail=0;" \ + "else " \ + "llfail=-1;" \ + "fi;" \ + "if test \\\"$llfail\\\" -ne 0 -a " \ + "\\\"$dhcpfail\\\" -ne 0; " \ + "then " \ + "setenv ipaddr $sipaddr; " \ + "setenv netmask $snetmask; " \ + "setenv gatewayip $sgatewayip; " \ + "fi;\0" \ + |