Are you ready for IPv6? Chris Kohlhoff

Outline: ●

IPv4 vs IPv6 – cheat sheet for developers

●

IPv6 support in Boost.Asio

●

Writing client programs

●

Writing server programs

IPv4 vs IPv6 Basics

IPv4 vs IPv6 Basics

Address ‒ binary representation IPv4

IPv6

32 bits

128 bits

IPv4 vs IPv6 Basics

Address ‒ string representation IPv4

IPv6

Dotted decimal address

Hex address

192.168.1.14

fec0:0:0:0:129a:ddff:fea7:529e

IPv4 vs IPv6 Basics

Address ‒ string representation IPv4

IPv6

Dotted decimal address

Hex address

192.168.1.14

fec0::129a:ddff:fea7:529e

At most one run of 0s may be “compressed”

IPv4 vs IPv6 Basics

Endpoint ‒ string representation IPv4

IPv6

192.168.1.14:12345

[fec0::129a:ddff:fea7:529e]:12345

IPv4 vs IPv6 Basics

Loopback address IPv4

IPv6

127.0.0.1

::1

IPv4 vs IPv6 Basics

Any address IPv4

IPv6

0.0.0.0

::

Sometimes you might also see 0::0

IPv6 Support in Boost.Asio

IPv6 Support in Boost.Asio

Principles: ●

Keep most user code independent of IP version

●

Avoid imposing dynamic memory allocation

IPv6 Support in Boost.Asio

Principles: ●

Keep most user code independent of IP version

●

Avoid imposing dynamic memory allocation

→ Use a variant approach

IPv6 Support in Boost.Asio

Resolver

Protocol

returns

Address

Endpoint Endpoint Endpoint

Port Number

IPv6 Support in Boost.Asio

Protocol: ●

For TCP, use asio::ip::tcp

●

For UDP, use asio::ip::udp

IPv6 Support in Boost.Asio udp my_protocol = udp::v4();

or udp my_protocol = udp::v6();

IPv6 Support in Boost.Asio udp my_protocol = udp::v4();

or udp my_protocol = udp::v6(); // ...

udp::socket sock(io_service, my_protocol);

IPv6 Support in Boost.Asio udp my_protocol = udp::v4();

or udp my_protocol = udp::v6(); // ...

udp::socket sock(io_service); sock.open(my_protocol);

IPv6 Support in Boost.Asio udp my_protocol = udp::v4();

or udp my_protocol = udp::v6(); // ...

if (my_protocol == udp::v6()) ...

IPv6 Support in Boost.Asio

Address: ●

Protocol independent ‒ asio::ip::address

●

IPv4 ‒ asio::ip::address_v4

●

IPv6 ‒ asio::ip::address_v6

IPv6 Support in Boost.Asio const char* ip_address_string = ...; address my_address = address::from_string(ip_address_string);

// ...

IPv4 dotted decimal or IPv6 hex address

std::string s = my_address.to_string();

IPv6 Support in Boost.Asio address my_address = address_v4::loopback(); // ... address my_address = address_v6::loopback();

IPv6 Support in Boost.Asio address my_address = address_v4::any(); // ... address my_address = address_v6::any();

IPv6 Support in Boost.Asio if (my_address.is_loopback()) ... New in Boost 1.47

if (my_address.is_unspecified()) ... if (my_address.is_multicast()) ...

IPv6 Support in Boost.Asio address_v4 my_address_v4 = ...; address my_address = my_address_v4; // ...

if (my_address.is_v4()) { address_v4 a = my_address.to_v4(); ... }

IPv6 Support in Boost.Asio address_v6 my_address_v6 = ...; address my_address = my_address_v6; // ...

if (my_address.is_v6()) { address_v6 a = my_address.to_v6(); ... }

IPv6 Support in Boost.Asio const char* ip_address_string = ...; address_v6 my_address_v6 = address_v6::from_string(ip_address_string);

// ...

IPv6 hex address only

std::string s = my_address_v6.to_string();

IPv6 Support in Boost.Asio address_v6::bytes_type raw_address_bytes; address_v6 my_address_v6(raw_address_bytes); // ...

address_v6::bytes_type bytes = my_address_v6.to_bytes();

array

IPv6 Support in Boost.Asio address_v4 my_address_v4 = ...; address_v6 my_address_v6 = address_v6::v4_mapped(my_address_v4);

// ... if (my_address_v6.is_v4_mapped()) { address_v4 a = my_address_v6.to_v4(); }

IPv6 Support in Boost.Asio address_v4 my_address_v4 = ...; address_v6 my_address_v6 = address_v6::v4_compatible(my_address_v4);

// ... if (my_address_v6.is_v4_compatible()) { address_v4 a = my_address_v6.to_v4(); }

IPv6 Support in Boost.Asio

Endpoint: ●

Always protocol independent

●

For TCP ‒ asio::ip::tcp::endpoint

●

For UDP ‒ asio::ip::udp::endpoint

IPv6 Support in Boost.Asio

Endpoint: ●

Always protocol independent

●

For TCP ‒ asio::ip::tcp::endpoint

●

For UDP ‒ asio::ip::udp::endpoint

Implemented as: template class basic_endpoint;

IPv6 Support in Boost.Asio udp::endpoint my_endpoint1(udp::v4(), 12345); // ... udp::endpoint my_endpoint2(udp::v6(), 12345); // ... address my_address = ...; udp::endpoint my_endpoint3(my_address, 12345);

IPv6 Support in Boost.Asio udp::endpoint my_endpoint = ...; // ... address my_address = my_endpoint.address(); // ... unsigned short my_port = my_endpoint.port(); // ... udp my_protocol = my_endpoint.protocol();

IPv6 Support in Boost.Asio

Resolver: ●

●

Obtain endpoints corresponding to host and service names Usually uses DNS

IPv6 Support in Boost.Asio udp::resolver::query my_query("host.name", "daytime"); // ... udp::resolver resolver(io_service); udp::resolver::iterator iter = resolver.resolve(my_query), end; while (iter != end) { cout << iter->endpoint() << std::endl; ++iter; }

One query can resolve to both IPv4 and IPv6 endpoints

IPv6 Support in Boost.Asio udp::resolver::query my_query1("host.name", "daytime"); // ... udp::resolver::query my_query2(udp::v4(), "host.name", "daytime"); // ... udp::resolver::query my_query3(udp::v6(), "host.name", "daytime");

IPv6 Support in Boost.Asio

Socket options: ● ●

Mostly protocol independent Automatically applies correct option based on socket's protocol

IPv6 Support in Boost.Asio udp::socket sock(io_service, my_protocol); // ...

sock.set_option(ip::unicast::hops(128));

For IPv4, uses IPPROTO_IP/IP_TTL For IPv6, uses IPPROTO_IPV6/IPV6_UNICAST_HOPS

Writing Client Programs

Writing Client Programs

Approaches for TCP clients: ●

Keep source code “protocol independent”

●

Prefer endpoints over addresses

●

Attempt connection to all available hosts

Writing Client Programs tcp::resolver resolver(io_service); tcp::resolver::query q("www.boost.org", "http"); tcp::resolver::iterator iter = resolver.resolve(q), end;

One query can resolve to multiple endpoints

Writing Client Programs tcp::resolver resolver(io_service); tcp::resolver::query q("www.boost.org", "http"); tcp::resolver::iterator iter = resolver.resolve(q), end;

tcp::socket sock(io_service); error_code ec = asio::error::not_found; while (iter != end && ec) { sock.close(ec); sock.connect(*iter, ec); ++iter; } if (ec) throw system_error(ec);

Try each endpoint until one works

Writing Client Programs tcp::resolver resolver(io_service); tcp::resolver::query q("www.boost.org", "http");

tcp::socket sock(io_service); asio::connect(sock, resolver.resolve(q));

New in Boost 1.47

Writing Client Programs tcp::resolver resolver(io_service); tcp::resolver::query q("www.boost.org", "http"); Reality check: IPv6 is vector endpoints( unlikely to be available yet resolver.resolve(q), tcp::resolver::iterator()); stable_partition(endpoints.begin(), endpoints.end(), is_ipv4); tcp::socket sock(io_service); error_code ec = asio::error::not_found; for (vector::iterator iter = endpoints.begin(); iter != endpoints.end() && ec; ++iter) { sock.close(ec); sock.connect(*iter, ec); } if (ec) throw system_error(ec); bool is_ipv4(const tcp::endpoint& endpoint) { return endpoint.protocol() == tcp::v4(); }

Writing Client Programs tcp::resolver resolver(io_service); tcp::resolver::query q("www.boost.org", "http"); vector endpoints( resolver.resolve(q), tcp::resolver::iterator()); stable_partition(endpoints.begin(), endpoints.end(), is_ipv4); tcp::socket sock(io_service); asio::connect(sock, endpoints.begin(), endpoints.end());

New in Boost 1.47

bool is_ipv4(const tcp::endpoint& endpoint) { return endpoint.protocol() == tcp::v4(); }

Writing Client Programs

Approaches for UDP clients: ●

Keep source code “protocol independent”

●

Use endpoints or addresses

Writing Client Programs const char* ip_address_string = ...; // IPv4 or IPv6 string representation udp::resolver resolver(io_service); udp::resolver::query q( ip_address_string, "50555", udp::resolver::query::numeric_host); udp::endpoint endpoint = *resolver.resolve(q); udp::socket sock(io_service); sock.open(endpoint.protocol()); sock.send_to(..., endpoint);

Writing Client Programs const char* ip_address_string = ...; // IPv4 or IPv6 string representation ip::address address = ip::address::from_string(ip_address_string); udp::endpoint endpoint(address, 50555);

udp::socket sock(io_service); sock.open(endpoint.protocol()); sock.send_to(..., endpoint);

Writing Server Programs

Writing Server Programs

The deployment environment: ●

Systems with both IPv4 and IPv6

●

Systems with IPv4 only

Writing Server Programs

The deployment environment: ●

●

Systems with both IPv4 and IPv6 ●

Dual stack

●

Separate stacks

Systems with IPv4 only

Writing Server Programs

The deployment environment is complex: ●

Systems with both IPv4 and IPv6 ●

Dual stack – –

●

●

Enabled by default Disabled by default

Separate stacks

Systems with IPv4 only

Writing Server Programs

Approaches for TCP servers: ●

●

Exactly one acceptor ●

Supports dual stack

●

Supports IPv6 only

●

Supports IPv4 only

Up to two acceptors ●

Supports all environments

Writing Server Programs

Exactly one acceptor: const char* listen_address = ...; // Typically "0.0.0.0" or "::" ip::address address = ip::address::from_string(listen_address); tcp::endpoint endpoint(address, 50555); tcp::acceptor acceptor(io_service, endpoint);

Writing Server Programs

Exactly one acceptor: const char* listen_address = ...; // Typically "0.0.0.0" or "::" ip::address address = ip::address::from_string(listen_address); tcp::endpoint endpoint(address, 50555); tcp::acceptor acceptor(io_service, endpoint.protocol()); if (endpoint.protocol() == tcp::v6()) { error_code ec; acceptor.set_option(ip::v6_only(false), ec); // Call succeeds only on dual stack systems. } acceptor.bind(endpoint); acceptor.listen();

Writing Server Programs

Up to two acceptors ‒ option 1: error_code ec; tcp::acceptor acceptor_v4(io_service); tcp::acceptor acceptor_v6(io_service); acceptor_v4.open(tcp::v4(), ec); if (!ec) { acceptor_v4.bind(tcp::endpoint(tcp::v4(), 50555)); acceptor_v4.listen(); } acceptor_v6.open(tcp::v6(), ec); if (!ec) { acceptor_v6.set_option(ip::v6_only(true)); acceptor_v6.bind(tcp::endpoint(tcp::v6(), 50555)); acceptor_v6.listen(); }

Writing Server Programs

Up to two acceptors ‒ option 2: ip::v6_only v6_only; acceptor_v6.open(tcp::v6(), ec); if (!ec) { acceptor_v6.get_option(v6_only); acceptor_v6.bind(tcp::endpoint(tcp::v6(), 50555)); acceptor_v6.listen(); } if (!acceptor_v6.is_open() || v6_only) { acceptor_v4.open(tcp::v4(), ec); if (!ec) { acceptor_v4.bind(tcp::endpoint(tcp::v4(), 50555)); acceptor_v4.listen(); } }

Writing Server Programs

Up to two acceptors ‒ option 3: ip::v6_only v6_only(false); acceptor_v6.open(tcp::v6(), ec); if (!ec) { acceptor_v6.set_option(v6_only, ec); acceptor_v6.get_option(v6_only); acceptor_v6.bind(tcp::endpoint(tcp::v6(), 50555)); acceptor_v6.listen(); } if (!acceptor_v6.is_open() || v6_only) { acceptor_v4.open(tcp::v4(), ec); if (!ec) { acceptor_v4.bind(tcp::endpoint(tcp::v4(), 50555)); acceptor_v4.listen(); } }

Writing Server Programs

Approaches for UDP servers: ●

●

Exactly one socket ●

Supports dual stack

●

Supports IPv6 only

●

Supports IPv4 only

Up to two sockets ●

Supports all environments

Writing Server Programs

Exactly one socket: const char* listen_address = ...; // Typically "0.0.0.0" or "::" ip::address address = ip::address::from_string(listen_address); udp::endpoint endpoint(address, 50555); udp::socket sock(io_service, endpoint);

Writing Server Programs

Exactly one socket: const char* listen_address = ...; // Typically "0.0.0.0" or "::" ip::address address = ip::address::from_string(listen_address); udp::endpoint endpoint(address, 50555); udp::socket sock(io_service, endpoint.protocol()); if (endpoint.protocol() == udp::v6()) { error_code ec; sock.set_option(ip::v6_only(false), ec); // Call succeeds only on dual stack systems. } sock.bind(endpoint);

Writing Server Programs

Up to two sockets ‒ option 1: error_code ec; udp::socket socket_v4(io_service); udp::socket socket_v6(io_service); socket_v4.open(udp::v4(), ec); if (!ec) { socket_v4.bind(udp::endpoint(udp::v4(), 50555)); } socket_v6.open(udp::v6(), ec); if (!ec) { socket_v6.set_option(ip::v6_only(true)); socket_v6.bind(udp::endpoint(udp::v6(), 50555)); }

Writing Server Programs

Up to two sockets ‒ option 2: ip::v6_only v6_only; socket_v6.open(udp::v6(), ec); if (!ec) { socket_v6.get_option(v6_only); socket_v6.bind(udp::endpoint(udp::v6(), 50555)); } if (!socket_v6.is_open() || v6_only) { socket_v4.open(udp::v4(), ec); if (!ec) { socket_v4.bind(udp::endpoint(udp::v4(), 50555)); } }

Writing Server Programs

Up to two sockets ‒ option 3: ip::v6_only v6_only(false); socket_v6.open(udp::v6(), ec); if (!ec) { socket_v6.set_option(v6_only, ec); socket_v6.get_option(v6_only); socket_v6.bind(udp::endpoint(udp::v6(), 50555)); } if (!socket_v6.is_open() || v6_only) { socket_v4.open(udp::v4(), ec); if (!ec) { socket_v4.bind(udp::endpoint(udp::v4(), 50555)); } }

Summary

Summary ●

Prefer protocol-independent approaches

●

Remember to try all endpoints

●

Choose designs appropriate to target environment

Are you ready for IPv6? - GitHub

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