pfSense

		// Group IPv6 addresses by their flags

		$address_flags = [

			'linklocal' => [],

			'anycast' => [],

			'tentative' => [],

			'duplicated' => [],

			'detached' => [],

			'deprecated' => [],

			'autoconf' => [],

			'temporary' => [],

			'prefer_source' => [],

			'no_flag' => []

		];

		foreach ($v6addrs as $addrs) {

			$has_flag = false;

			foreach (array_keys($addrs) as $key) {

				if (isset($address_flags[$key])) {

					$has_flag = true;

					$address_flags[$key][] = $addrs['addr'];

				}

			}

			if (!$has_flag) {

				$address_flags['no_flag'][] = $addrs['addr'];

			}

		}

		/**

		 * Create a list of IPv6 addresses that prioritizes the most

		 * "valid" source address. Each key in the array references a

		 * group of IPv6 addresses. Each key is assigned the first GUA of

		 * the respective group. If a GUA for the group does not exist,

		 * then the first IPv6 address of the group is assigned.

		 * 

		 * A "preferred" address has the prefer_source flag and does not

		 * have any flags considered "invalid".

		 * 

		 * A "manual" address does not have any flags.

		 * 

		 * A "valid" address does not have any flags considered "invalid".

		 * 

		 * An "invalid" address must have any of the following flags:

		 * deprecated, duplicated, tentative, or detached. It may have

		 * additional flags that need to be considered. The selected

		 * address is based on the following flag order:

		 * prefer_source, temporary, anycast, autoconf, deprecated, duplicated

		 * tentative, and lastly detached.

		 * 

		 * A "linklocal" address has the linklocal flag.

		 */

		$address_priority_list = [

			'preferred' => null,

			'manual' => null,

			'valid' => null,

			'invalid' => null,

			'linklocal' => null

		];

		// The merge/intersect/diff order here is important.

		$candidate_addresses = array_unique(array_merge($address_flags['prefer_source'], $address_flags['no_flag'], $address_flags['temporary'], $address_flags['anycast'], $address_flags['autoconf']));

		$invalid_addresses = array_unique(array_merge($address_flags['deprecated'], $address_flags['duplicated'], $address_flags['tentative'], $address_flags['detached']));

		$invalid_addresses = array_unique(array_merge(array_intersect($candidate_addresses, $invalid_addresses), $invalid_addresses));

		$valid_addresses = array_diff($candidate_addresses, $invalid_addresses);

		// Get a preferred address.

		$temp_list = [];

		foreach ($address_flags['prefer_source'] as $address) {

			if (in_array($address, $valid_addresses)) {

				if (is_v6gua($address)) {

					$temp_list = [$address];

					break;

				} else {

					$temp_list[] = $address;

				}

			}

		}

		if (!empty($temp_list)) {

			$address_priority_list['preferred'] = $temp_list[array_key_first($temp_list)];

		}

		// Get a manual address.

		$temp_list = [];

		foreach ($address_flags['no_flag'] as $address) {

			if (is_v6gua($address)) {

				$temp_list = [$address];

				break;

			} else {

				$temp_list[] = $address;

			}

		}

		if (!empty($temp_list)) {

			$address_priority_list['manual'] = $temp_list[array_key_first($temp_list)];

		}

		// Get a valid address.

		$temp_list = [];

		foreach ($valid_addresses as $address) {

			if (is_v6gua($address)) {

				$temp_list = [$address];

				break;

			} else {

				$temp_list[] = $address;

			}

		}

		if (!empty($temp_list)) {

			$address_priority_list['valid'] = $temp_list[array_key_first($temp_list)];

		}

		// Get an invalid address.

		$temp_list = [];

		foreach ($invalid_addresses as $address) {

			if (is_v6gua($address)) {

				$temp_list = [$address];

				break;

			} else {

				$temp_list[] = $address;

			}

		}

		if (!empty($temp_list)) {

			$address_priority_list['invalid'] = $temp_list[array_key_first($temp_list)];

		}

		// Get a link-local address

		if (!empty($address_flags['linklocal'])) {

			$address_priority_list['linklocal'] = $address_flags[array_key_first($address_flags['linklocal'])];

		}

		$selected_address = null;

		if (isset($address_priority_list['preferred']) && is_v6gua($address_priority_list['preferred'])) {

			$selected_address = $address_priority_list['preferred'];

		} elseif (isset($address_priority_list['manual']) && is_v6gua($address_priority_list['manual'])) {

			$selected_address = $address_priority_list['manual'];

		} elseif (isset($address_priority_list['valid']) && is_v6gua($address_priority_list['valid'])) {

			$selected_address = $address_priority_list['valid'];

		} elseif (isset($address_priority_list['preferred'])) {

			$selected_address = $address_priority_list['preferred'];

		} elseif (isset($address_priority_list['manual'])) {

			$selected_address = $address_priority_list['manual'];

		} elseif (isset($address_priority_list['valid'])) {

			$selected_address = $address_priority_list['valid'];

		} elseif (isset($address_priority_list['invalid'])) {

			$selected_address = $address_priority_list['invalid'];

		} elseif (isset($address_priority_list['linklocal'])) {

			$selected_address = $address_priority_list['linklocal'];

		} else {

			// Unexpected condition

			$v6addr = $v6addrs[array_key_first($v6addrs)];

		}

			if ($addr['addr'] == $selected_address) {