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authorDenis Vlasenko <vda.linux@googlemail.com>2006-10-26 17:21:13 +0000
committerDenis Vlasenko <vda.linux@googlemail.com>2006-10-26 17:21:13 +0000
commit670a6626cabc1498f32b35f959591f8621d8447e (patch)
tree8fb308735a25ded208a2fcbf2561de6f13bf1408 /docs
parentebe578ab2fc19e9ce0d876a10fc389b018a30eba (diff)
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add ipv6 developer doc
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-rw-r--r--docs/ipv4_ipv6.txt222
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diff --git a/docs/ipv4_ipv6.txt b/docs/ipv4_ipv6.txt
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1We need better network address conv helpers.
2This is what our applets want:
3
4 sockaddr -> hostname
5udhcp: hostname -> ipv4 addr
6nslookup: hostname -> list of names - done
7tftp: host,port -> sockaddr
8nc: host,port -> sockaddr
9inetd: ?
10traceroute: ?, hostname -> ipv4 addr
11arping hostname -> ipv4 addr
12ping6 hostname -> ipv6 addr
13ifconfig hostname -> ipv4 addr (FIXME error check?)
14ipcalc ipv4 addr -> hostname
15syslogd hostname -> sockaddr
16inet_common.c: buggy. hostname -> ipv4 addr
17mount hostname -> sockaddr_in
18
19==================
20HOWTO get rid of inet_ntoa/aton:
21
22foo.sin_addr.s_addr = inet_addr(cp);
23-
24inet_pton(AF_INET, cp, &foo.sin_addr);
25
26inet_aton(cp, &foo.sin_addr);
27-
28inet_pton(AF_INET, cp, &foo.sin_addr);
29
30ptr = inet_ntoa(foo.sin_addr);
31-
32char str[INET_ADDRSTRLEN];
33ptr = inet_ntop(AF_INET, &foo.sin_addr, str, sizeof(str));
34
35===================
36
37 struct addrinfo {
38 int ai_flags;
39 int ai_family;
40 int ai_socktype;
41 int ai_protocol;
42 size_t ai_addrlen;
43 struct sockaddr *ai_addr;
44 char *ai_canonname;
45 struct addrinfo *ai_next;
46 };
47 int getaddrinfo(const char *node, const char *service,
48 const struct addrinfo *hints,
49 struct addrinfo **res);
50
51 void freeaddrinfo(struct addrinfo *res);
52
53 const char *gai_strerror(int errcode);
54
55 The members ai_family, ai_socktype, and ai_protocol have the same meaning
56 as the corresponding parameters in the socket(2) system call. The getad-
57 drinfo(3) function returns socket addresses in either IPv4 or IPv6 address
58 family, (ai_family will be set to either AF_INET or AF_INET6).
59
60 The hints parameter specifies the preferred socket type, or protocol. A
61 NULL hints specifies that any network address or protocol is acceptable.
62 If this parameter is not NULL it points to an addrinfo structure whose
63 ai_family, ai_socktype, and ai_protocol members specify the preferred
64 socket type. AF_UNSPEC in ai_family specifies any protocol family (either
65 IPv4 or IPv6, for example). 0 in ai_socktype or ai_protocol specifies
66 that any socket type or protocol is acceptable as well. The ai_flags mem-
67 ber specifies additional options, defined below. Multiple flags are spec-
68 ified by logically OR-ing them together. All the other members in the
69 hints parameter must contain either 0, or a null pointer.
70
71 The node or service parameter, but not both, may be NULL. node specifies
72 either a numerical network address (dotted-decimal format for IPv4, hex-
73 adecimal format for IPv6) or a network hostname, whose network addresses
74 are looked up and resolved. If hints.ai_flags contains the AI_NUMERICHOST
75 flag then the node parameter must be a numerical network address. The
76 AI_NUMERICHOST flag suppresses any potentially lengthy network host
77 address lookups.
78
79 The getaddrinfo(3) function creates a linked list of addrinfo structures,
80 one for each network address subject to any restrictions imposed by the
81 hints parameter. The ai_canonname field of the first of these addrinfo
82 structures is set to point to the official name of the host, if
83 hints.ai_flags includes the AI_CANONNAME flag. ai_family, ai_socktype,
84 and ai_protocol specify the socket creation parameters. A pointer to the
85 socket address is placed in the ai_addr member, and the length of the
86 socket address, in bytes, is placed in the ai_addrlen member.
87
88 If node is NULL, the network address in each socket structure is initial-
89 ized according to the AI_PASSIVE flag, which is set in hints.ai_flags.
90 The network address in each socket structure will be left unspecified if
91 AI_PASSIVE flag is set. This is used by server applications, which intend
92 to accept client connections on any network address. The network address
93 will be set to the loopback interface address if the AI_PASSIVE flag is
94 not set. This is used by client applications, which intend to connect to
95 a server running on the same network host.
96
97 If hints.ai_flags includes the AI_ADDRCONFIG flag, then IPv4 addresses are
98 returned in the list pointed to by result only if the local system has at
99 least has at least one IPv4 address configured, and IPv6 addresses are
100 only returned if the local system has at least one IPv6 address config-
101 ured.
102
103 If hint.ai_flags specifies the AI_V4MAPPED flag, and hints.ai_family was
104 specified as AF_INET6, and no matching IPv6 addresses could be found, then
105 return IPv4-mapped IPv6 addresses in the list pointed to by result. If
106 both AI_V4MAPPED and AI_ALL are specified in hints.ai_family, then return
107 both IPv6 and IPv4-mapped IPv6 addresses in the list pointed to by result.
108 AI_ALL is ignored if AI_V4MAPPED is not also specified.
109
110 service sets the port number in the network address of each socket struc-
111 ture. If service is NULL the port number will be left uninitialized. If
112 AI_NUMERICSERV is specified in hints.ai_flags and service is not NULL,
113 then service must point to a string containing a numeric port number.
114 This flag is used to inhibit the invocation of a name resolution service
115 in cases where it is known not to be required.
116
117
118==============
119
120 int getnameinfo(const struct sockaddr *sa, socklen_t salen,
121 char *host, size_t hostlen,
122 char *serv, size_t servlen, int flags);
123
124 The getnameinfo(3) function is defined for protocol-independent
125 address-to-nodename translation. It combines the functionality
126 of gethostbyaddr(3) and getservbyport(3) and is the inverse of
127 getaddrinfo(3). The sa argument is a pointer to a generic socket address
128 structure (of type sockaddr_in or sockaddr_in6) of size salen that
129 holds the input IP address and port number. The arguments host and
130 serv are pointers to buffers (of size hostlen and servlen respectively)
131 to hold the return values.
132
133 The caller can specify that no hostname (or no service name) is required
134 by providing a NULL host (or serv) argument or a zero hostlen (or servlen)
135 parameter. However, at least one of hostname or service name must be requested.
136
137 The flags argument modifies the behaviour of getnameinfo(3) as follows:
138
139 NI_NOFQDN
140 If set, return only the hostname part of the FQDN for local hosts.
141
142 NI_NUMERICHOST
143 If set, then the numeric form of the hostname is returned.
144 (When not set, this will still happen in case the node's name
145 cannot be looked up.)
146
147 NI_NAMEREQD
148 If set, then a error is returned if the hostname cannot be looked up.
149
150 NI_NUMERICSERV
151 If set, then the service address is returned in numeric form,
152 for example by its port number.
153
154 NI_DGRAM
155 If set, then the service is datagram (UDP) based rather than stream
156 (TCP) based. This is required for the few ports (512-514) that have different
157 services for UDP and TCP.
158
159=================
160
161Modified IPv6-aware C code:
162
163 struct addrinfo *res, *aip;
164 struct addrinfo hints;
165 int sock = -1;
166 int error;
167
168 /* Get host address. Any type of address will do. */
169 bzero(&hints, sizeof(hints));
170 hints.ai_flags = AI_ALL|AI_ADDRCONFIG;
171 hints.ai_socktype = SOCK_STREAM;
172
173 error = getaddrinfo(hostname, servicename, &hints, &res);
174 if (error != 0) {
175 (void) fprintf(stderr,
176 "getaddrinfo: %s for host %s service %s\n",
177 gai_strerror(error), hostname, servicename);
178 return (-1);
179 }
180 /* Try all returned addresses until one works */
181 for (aip = res; aip != NULL; aip = aip->ai_next) {
182 /*
183 * Open socket. The address type depends on what
184 * getaddrinfo() gave us.
185 */
186 sock = socket(aip->ai_family, aip->ai_socktype, aip->ai_protocol);
187 if (sock == -1) {
188 perror("socket");
189 freeaddrinfo(res);
190 return (-1);
191 }
192
193 /* Connect to the host. */
194 if (connect(sock, aip->ai_addr, aip->ai_addrlen) == -1) {
195 perror("connect");
196 (void) close(sock);
197 sock = -1;
198 continue;
199 }
200 break;
201 }
202 freeaddrinfo(res);
203
204Note that for new applications, if you write address-family-agnostic data structures,
205there is no need for porting.
206
207However, when it comes to server-side programming in C/C++, there is an additional wrinkle.
208Namely, depending on whether your application is written for a dual-stack platform, such
209as Solaris or Linux, or a single-stack platform, such as Windows, you would need to
210structure the code differently.
211
212Here's the corresponding server C code for a dual-stack platform:
213
214 int ServSock, csock;
215 struct sockaddr addr, from;
216 ...
217 ServSock = socket(AF_INET6, SOCK_STREAM, PF_INET6);
218 bind(ServSock, &addr, sizeof(addr));
219 do {
220 csock = accept(ServSocket, &from, sizeof(from));
221 doClientStuff(csock);
222 } while (!finished);
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