ip6.7p (2010 09)

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IPv6(7P) IPv6(7P)

• The second type is termed as IPv4-mapped IPv6 address and is of the form

0:0:0:0:0:ffff:d.d.d.d

. This address facilitates IPv6 applications to interoperate with

IPv4 applications. Applications can automatically generate this address using

getad-

drinfo() (see getaddrinfo (3N)) when the speciﬁed host has only IPv4 address.

IPv6 Multicast

As with IPv4, an application joins a multicast group on a network interface in order to receive multicast

datagrams sent on the network to which that interface connects.

The application must also bind to the destination port number in order to receive datagrams that are sent

to that port number. If the application binds to the unspeciﬁed address (all zeroes), it may receive all

datagrams that are sent to the port number. If the application binds to a multicast group address, it may

receive only datagrams sent to that group and port number. It is not necessary to join a multicast group

in order to send datagrams to it.

For each multicast group that an application joins on a given socket and network interface, there is an

associated ﬁlter mode and source list. The ﬁlter mode can be "exclude" mode or "include" mode. The

source list is a set of IP addresses which will be compared to the source addresses of received multicast

datagrams.

An application uses "exclude" mode when it wants to block reception of multicast datagrams from a

speciﬁc set of sources, while allowing multicast datagrams from all other sources.

For groups in "exclude" mode, the source list may be empty, thus allowing reception of multicast

datagrams from all sources. An application uses "include" mode when it wants to allow reception of mul-

ticast datagrams from a speciﬁc set of sources, while blocking multicast datagrams from all other sources.

For groups in "include" mode, the source list needs to contain at least one member in order for the appli-

cation to stay joined to the group; removing the last address from an "include" mode source list will cause

the application to leave the group.

Multicast socket options are not supported on SOCK_STREAM sockets.

IPv6 Socket Options

New socket options are deﬁned for IPv6 to send and receive extension headers and to exchange other

optional information between the kernel and application. The options are supported at the

IPPROTO_IPV6 protocol level. The type of the variable pointed to by the optval parameter is indicated

in parenthesis.

IPV6_UNICAST_HOPS

(integer) Sets or gets the hop limit used in outgoing unicast packets.

When this option is set using

setsockopt() (see setsockopt (2)), the

new option value speciﬁed is used as the hop limit for all subsequent uni-

cast packets sent via that socket. Valid values are in the range 0-255

(both inclusive) and the default value is 64. For example,

int hoplimit = 50;

setsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,

&hoplimit, sizeof(hoplimit));

This option can be used with

getsockopt() (see getsockopt (2)) to

determine the hop limit value the system will use for subsequent unicast

packets sent via that socket.

IPV6_MULTICAST_HOPS

(integer) Sets or gets the hop limit used in outgoing multicast packets.

When this option is set, the new option value speciﬁed is used as the hop

limit for all subsequent multicast packets sent via that socket. Valid

values are in the range 0-255 (both inclusive) and the default value is 1.

IPV6_MULTICAST_IF (integer) Sets the interface to use for outgoing multicast packets. The

option value is the index of the selected outgoing interface. For example,

unsigned int index;

index = if_nametoindex("lan0");

setsockopt(s, IPPROTO_IPV6, IPV6_MULTICAST_IF,

&index, sizeof(index));

IPV6_MULTICAST_LOOP

(boolean) Enables or disables loopback in the IP layer for multicast

datagrams sent through this socket. The value of the variable pointed to

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