bash: using sed to replace end of line between substring -

i trying relatively simple not sure how it.

i have mac address follows:

xx:yy:yy:zz:yy:yy

i modify :yy: @ end of string becomes :01: using our example above, becomes:

xx:yy:yy:zz:01:yy

basically characters between last : : in string.

i trying following wasn't working:

echo "$var" | sed 's/:*:*$/:01:/'

i know simple question, appreciated please.

awk easier solve kind of problem:

awk -f: -v ofs=":" '$5="01"'

example:

kent$  echo "xx:yy:yy:zz:yy:yy"|awk -f: -v ofs=":" '$5="01"' xx:yy:yy:zz:01:yy

DIs