Tribblix: manual page: ndp.4p

NDP(4P) Protocols NDP(4P)

NAME

ndp, NDP - Neighbor Discovery Protocol

SYNOPSIS

#include <sys/socket.h>
#include <sys/sockio.h>
#include <netinet/in.h>
#include <net/if.h>

s = socket(PF_INET6, SOCK_DGRAM, 0);

struct lifreq lifr;
ioctl(s, SIOCLIFGETND, &lifr);
ioctl(s, SIOCLIFSETND, &lifr);
ioctl(s, SIOCLIFDELND, &lifr);

DESCRIPTION

The Neighbor Discovery Protocol (NDP) is a protocol used to distribute
and request information about neighboring IPv6 systems on the local
network, much like ARP(4P) for IPv4. NDP is also responsible for
spreading information about the network gateway and how hosts should
configure themselves (see in.ndpd(8) for more on how this happens).

APPLICATION PROGRAMMING INTERFACE

The operating system provides several ioctls to help manipulate the
mappings obtained through NDP. They are SIOCLIFGETND, SIOCLIFSETND,
and SIOCLIFDELND, for getting, setting, and deleting respectively.
Each of these ioctls takes a struct lifreq (see if(4P) for details),
where the lifr_lifru field is of type struct lif_nd_req:

typedef struct lif_nd_req {
struct sockaddr_storage lnr_addr;
uint8_t lnr_state_create;
uint8_t lnr_state_same_lla;
uint8_t lnr_state_diff_lla;
int lnr_hdw_len;
int lnr_flags;
int lnr_pad0;
char lnr_hdw_addr[ND_MAX_HDW_LEN];
} lif_nd_req_t;

The lnr_addr field should be filled in with an IPv6 address (see
sockaddr_in6(3SOCKET)), and the lnr_hdw_addr is the link-layer address
of length lnr_hdw_len.

State flags for lnr_state_create, lnr_state_same_lla, and
lnr_state_diff_lla can be set to one of the following values:

ND_UNCHANGED For ioctls that don't modify state

ND_INCOMPLETE Address resolution is currently in progress

ND_REACHABLE The link-layer address has recently been
reachable

ND_STALE The link-layer address may be unreachable, and
the system shouldn't do anything

ND_DELAY This entry hasn't yet started sending Neighbor
Solicitations

ND_PROBE The operating system is currently sending out
Neighbor Solicitations for the address

ND_UNREACHABLE The link-layer address is unreachable, and this
entry is going to be deleted.

When creating a new entry, the only valid values for lnr_state_create
are ND_REACHABLE and ND_STALE. Any other value will return EINVAL.
The lnr_state_same_lla and lnr_state_diff_lla fields are reserved for
future use and can be safely set to ND_UNCHANGED and ND_STALE
respectively.

Flags that can be placed in lnr_flags are:

NDF_ISROUTER_ON Mark this entry as being a router. This will
cause Neighbor Advertisements for this address
to be sent with the R-bit (Router).

NDF_ISROUTER_OFF If this entry was flagged as being a router,
remove the flag.

NDF_ANYCAST_ON Mark this entry as being for an anycast
address. This prevents sending Neighbor
Advertisements with the O-bit (Override).

NDF_ANYCAST_OFF If this entry was flagged as an anycast
address, remove the flag.

NDF_STATIC Prevent this entry from being deleted by the
system.

When using SIOCLIFGETND, these flags represent the current state of the
corresponding Neighbor Cache Entry. When using SIOCLIFSETND, these
flags represent what changes should be applied to the underlying entry.

The only fields that need to be set for the SIOCLIFGETND or
SIOCLIFDELND ioctls are lifr_name and lnr_addr. All other fields
should be zeroed out. After successfully getting an entry, the other
fields will be filled in. When using SIOCLIFSETND, all fields should
be set to an appropriate value, as described above, with the exception
of lnr_pad0, which is unused and only exists for padding purposes.

After performing the ioctl, the following errors may be returned
through the global errno variable:

EAFNOSUPPORT A non-IPv6 socket was used to perform the
ioctl.

EINVAL The request contents were bad. This could be
because conflicting flags were used, the
specified interface wasn't logical unit zero,
or another reason.

ENOMEM The system ran out of memory for internal data
structures.

ENXIO The specified interface does not exist.

EPERM The caller does not have permission to modify
the Neighbor Cache Entries associated with this
interface. They may be lacking the
PRIV_SYS_NET_CONFIG privilege (see
privileges(7)), or the interface is managed by
IPMP (IP Network Multipathing).

ESRCH There is no entry matching the specified
address.

EXAMPLES

The following examples demonstrate how to get and set NDP mappings
using the provided ioctls. They can be compiled by using a C compiler
and linking against the sockets library.

Example 1: Getting a mapping
$ gcc -Wall -lsocket -o get get.c
$ cat get.c
/*
* Example of getting a mapping for a node name.
*/
#include <strings.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <unistd.h>
#include <netdb.h>
#include <net/if.h>

int get(char *host) {
struct lifreq lifr;
struct addrinfo hints, *serverinfo, *p;
int err, s;

bzero(&hints, sizeof (struct addrinfo));
hints.ai_family = PF_INET6;
hints.ai_protocol = IPPROTO_IPV6;

if ((err = getaddrinfo(host, NULL, &hints, &serverinfo)) != 0) {
(void) fprintf(stderr, "Unable to lookup %s: %s\n", host,
gai_strerror(err));
return (1);
}

s = socket(AF_INET6, SOCK_DGRAM, 0);
if (s < 0) {
perror("Failed to open IPv6 socket");
return (1);
}

for (p = serverinfo; p != NULL; p = p->ai_next) {
/* Zero out structure */
bzero(&lifr, sizeof (struct lifreq));
(void) strlcpy(lifr.lifr_name, "net0",
sizeof (lifr.lifr_name));
(void) memcpy(&lifr.lifr_nd.lnr_addr, p->ai_addr,
sizeof (struct sockaddr_storage));

/* Get mapping */
if (ioctl(s, SIOCLIFGETND, &lifr) < 0) {
perror("Unable to get NDP mapping");
continue;
}

/*
* lifr.lifr_nd.lnr_hdw_addr now contains the MAC address,
* and can be used as desired.
*/
}

/*
* Clean up linked list.
*/
freeaddrinfo(serverinfo);
return (0);
}

int main(int argc, char *argv[]) {
if (argc < 2)
exit(1);
return (get(argv[1]));
}

Deleting a mapping would work similarly, except that instead of using
SIOCLIFGETND, you would instead use the SIOCLIFDELND ioctl.

Example 2: Adding a mapping
$ gcc -Wall -lsocket -o set set.c
$ cat set.c
/*
* Example of setting a mapping to an all-zero Ethernet address.
*/
#include <strings.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <unistd.h>
#include <netdb.h>
#include <net/if.h>

int set(char *host) {
struct lifreq lifr;
struct addrinfo hints, *serverinfo, *p;
int err, s;

bzero(&hints, sizeof (struct addrinfo));
hints.ai_family = PF_INET6;
hints.ai_protocol = IPPROTO_IPV6;

if ((err = getaddrinfo(host, NULL, &hints, &serverinfo)) != 0) {
(void) fprintf(stderr, "Unable to lookup %s: %s\n", host,
gai_strerror(err));
return (1);
}

s = socket(AF_INET6, SOCK_DGRAM, 0);
if (s < 0) {
perror("Failed to open IPv6 socket");
return (1);
}

for (p = serverinfo; p != NULL; p = p->ai_next) {
/* Zero out structure */
bzero(&lifr, sizeof (struct lifreq));
(void) strlcpy(lifr.lifr_name, "net0",
sizeof (lifr.lifr_name));
(void) memcpy(&lifr.lifr_nd.lnr_addr, p->ai_addr,
sizeof (struct sockaddr_storage));

lifr.lifr_nd.lnr_state_create = ND_REACHABLE;
lifr.lifr_nd.lnr_flags = NDF_STATIC;

/* Get mapping */
if (ioctl(s, SIOCLIFSETND, &lifr) < 0) {
perror("Unable to set NDP mapping");
continue;
}
}

/*
* Clean up linked list.
*/
freeaddrinfo(serverinfo);
return (0);
}

int main(int argc, char *argv[]) {
if (argc < 2)
exit(1);
return (set(argv[1]));
}

NAME

SYNOPSIS

DESCRIPTION

APPLICATION PROGRAMMING INTERFACE

EXAMPLES

SEE ALSO