| Table 1 IPv4 vs. IPv6: sockets API structures and constants
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| Feature
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IPv4
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IPv6
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Comments
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Protocol family.
First argument in socket().
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AF_INET
PF_INET
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AF_INET6
PF_INET6
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Address and protocol families are used interchangeably
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| Address family
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AF_INET
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AF_INET6
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In sockaddr family field
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| Inet address structure
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struct sockaddr_in
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struct sockaddr_in6
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Note: sockaddr_in6 is larger than sockaddr
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| Generic address structure
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struct sockaddr
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struct sockaddr_storage
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Only when used to allocate storage
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| IP address structure
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struct in_addr
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struct in6_addr
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| Loopback address
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INADDR_LOOPBACK
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in6addr_loopback
IN6ADDR_LOOPBACK_INIT
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Constant can only be used for structure initialization
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| Wildcard address for binding listeners and receivers
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in6addr_any
INADDR_ANY_INIT
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Constant can only be
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| Name to address
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gethostbyname()
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getaddrinfo()
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| Address to name
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gethostbyaddr()
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getnameinfo()
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| Free data structures returned by getaddrinfo()
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freeaddrinfo()
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getaddrinfo() is multithread safe
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| Report errors
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gai_strerror()
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Errors from getaddrinfo() and getnameinfo()
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| String to address
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inet_addr()
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inet_pton()
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Added family parameter
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| Address to string
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inet_ntoa()
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inet_ntop()
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Added family parameter
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| Socket option for TTL
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IP_TTL
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IPv6_UNICAST_HOPS
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Set TTL/hop limit
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| Get reserved port
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rresvport()
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rresvport_af()
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Used by rcmd()
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| Execute a command on a remote host
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rcmd()
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rcmd_af()
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Added family parameter
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