Which of the following is a correct statement concerning IPv6?
a) To show that IPv6 packets will be encapsulated in IPv4, the IPv6 protocol identifier is specified as the payload type.
b) The IP address size is expanded to 128 bits and a checksum is used for detecting errors in header information.
c) The header information has nothing equivalent to TTL (time to live) supported by IPv4, and there are no limits to the number of gateways through which data pass.
d) The adjacent node’s address is used as the loop back address, and it can be used for identifying a problem in case of an error.