Commands /etc/init/boot.local get started before some environment variables get initialized

The scripts at /etc/profile.d/* are executed in their own shells rather than sourced so the environment variables they set are not available anyway.What variables do you need? Can you make use of /etc/environment? Can you write the variables into a file in a var=value format from the appropriate scripts and source that file in your rc.local scripts?

This is from the Bash man page. You may find it helpful.

When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following com‐ mand were executed: if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi but the value of the PATH variable is not used to search for the file name.

The Bourne shell similarly uses the ENV variable.

There is no clear answer to your question. It depends whether the service which needs 172.16.5.243 is a SysV init script or a upstart job.

When it is a SysV init script, you can add dependencies with this header in the init script:

### BEGIN INIT INFO
# Provides:          scriptname
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Start daemon at boot time
# Description:       Enable service provided by daemon.
### END INIT INFO

When it is an Upstart script, take a look at this post. The interesting part is in the accepted answer:

start on (local-filesystems and net-device-up IFACE=eth0)