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# Copyright (c) 2007-2008 Roy Marples <roy@marples.name>
# Released under the 2-clause BSD license.
apipa_depend()
{
program /sbin/arping /bin/arping
}
_random_uint16()
{
# While POSIX does not require that /dev/urandom exist, it is a de-facto
# standard. In the case of Linux, and unlike BSD, this interface does
# not block in the event that the CSRNG has not yet been seeded.
# Still, this is acceptable because we do not require a guarantee that
# the entropy be cryptographically secure.
test -e /dev/urandom &&
printf %d 0x"$(LC_ALL=C od -vAn -N2 -tx1 /dev/urandom | tr -d '[:space:]')"
}
_random_apipa_octets()
{
local seed
# Attempt to generate a random uint16 to seed awk's RNG. The maximum
# value of RAND_MAX known to be portable is 32767. Clamp accordingly by
# discarding one bit's worth of data. Should the seed turn out to be
# empty, we instruct awk to seed based on the time of day, in seconds.
seed=$(_random_uint16) && : $(( seed >>= 1 ))
# For APIPA (RFC 3927), the 169.254.0.0/16 address block is
# reserved. This provides 65024 addresses, having accounted for the
# fact that the first and last /24 are reserved for future use.
awk -v seed="$seed" 'BEGIN {
if (seed != "") {
srand(seed)
} else {
srand()
}
for (i = 1; i < 255; i++) {
for (j = 0; j < 256; j++) {
printf("%f %d %d\n", rand(), i, j)
}
}
}' | sort -k 1,1 -n
}
apipa_start()
{
local addr rc
_exists || return
einfo "Searching for free addresses in 169.254.0.0/16"
eindent
exec 3>&1
addr=$(
_random_apipa_octets |
{
while read -r f1 f2 f3; do
next_addr="169.254.$f2.$f3"
vebegin "$next_addr/16" >&3
if ! arping_address "$next_addr" >&3; then
printf %s "$next_addr"
exit 0
fi
done
exit 1
}
)
rc=$?
exec 3>&-
if [ "$rc" = 0 ]; then
eval "config_${config_index}=\"\${addr}/16 broadcast 169.254.255.255\""
: $(( config_index -= 1 ))
veend 0
else
eerror "No free address found!"
fi
eoutdent
return "$rc"
}
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