In a small saucepan combine vinegar and orange peel. Bring to boiling; reduce heat. Simmer, uncovered, for 3 to 5 minutes or until vinegar is reduced to 1/4 cup. Remove from heat. Cover and let stand until cool. Pour mixture through a fine-mesh sieve; discard peel.
In a 4- to 6-quart heavy pot combine the reduced vinegar, sugar, and port. Bring to a full rolling boil over high heat, stirring constantly. Quickly stir in pectin. Return to a full rolling boil, stirring constantly. Boil hard for 1 minute, stirring constantly. Remove from heat. Quickly skim off foam with a metal spoon.
Ladle hot jelly into hot sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.
Process filled jars in a boiling-water canner for 10 minutes (start timing when water returns to boiling). Remove jars from canner; cool on wire racks. Makes 4 half-pints.