'\" te
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.TH ETHERS 3SOCKET "Feb 17, 2023"
.SH NAME
ethers, ether_ntoa, ether_ntoa_r, ether_aton, ether_aton_r, ether_ntohost, ether_hostton, ether_line \-
Ethernet address mapping operations
.SH SYNOPSIS
.nf
\fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lsocket\fR \fB -lnsl \fR [ \fIlibrary\fR ... ]
#include <sys/types.h>
#include <sys/ethernet.h>

\fBchar *\fR\fBether_ntoa\fR(\fBconst struct ether_addr *\fR\fIe\fR);
.fi

.LP
.nf
\fBchar *\fR\fBether_ntoa_r\fR(\fBconst struct ether_addr *\fR\fIe\fR, \fBchar *\fR\fIs\fR);
.fi

.LP
.nf
\fBstruct ether_addr *\fR\fBether_aton\fR(\fBconst char *\fR\fIs\fR);
.fi

.LP
.nf
\fBstruct ether_addr *\fR\fBether_aton_r\fR(\fBconst char *\fR\fIs\fR, \fBstruct ether_addr *\fR\fIe\fR);
.fi

.LP
.nf
\fBint\fR \fBether_ntohost\fR(\fBchar *\fR\fIhostname\fR, \fBconst struct ether_addr *\fR\fIe\fR);
.fi

.LP
.nf
\fBint\fR \fBether_hostton\fR(\fBconst char *\fR\fIhostname\fR, \fBstruct ether_addr *\fR\fIe\fR);
.fi

.LP
.nf
\fBint\fR \fBether_line\fR(\fBconst char *\fR\fIl\fR, \fBstruct ether_addr *\fR\fIe\fR, \fBchar *\fR\fIhostname\fR);
.fi

.SH DESCRIPTION
These routines are useful for mapping 48 bit Ethernet numbers to their ASCII
representations or their corresponding host names, and vice versa.
.sp
.LP
The function \fBether_ntoa()\fR converts a 48 bit Ethernet number pointed to by
\fIe\fR to its standard \fBASCII\fR representation; it returns a pointer to
the \fBASCII\fR string.  The representation is of the form
\fIx\fR\|:\|\fIx\fR\|:\|\fIx\fR\|:\|\fIx\fR\|:\|\fIx\fR\|:\|\fIx\fR where
\fIx\fR is a hexadecimal number between \fB0\fR and \fBff\fR.  The function
\fBether_aton()\fR converts an \fBASCII\fR string in the standard
representation back to a 48 bit Ethernet number; the function returns
\fINULL\fR if the string cannot be scanned successfully.
.sp
.LP
The functions \fBether_ntoa()\fR and \fBether_aton()\fR return values in
per-thread buffers, one for each function. A second call to one of these
functions will overwrite the previous value. The functions
\fBether_ntoa_r()\fR and \fBether_aton_r()\fR behave identically to
their non-reentrant versions; however, instead of using a per-thread
buffer, they use caller supplied buffers. It is the callers
responsibility to ensure that the character buffer passed to
\fBether_ntoa_r()\fR is at least \fBETHERADDRSTRL\fR bytes large -- the
minimum size to hold the ASCII representation of a 48 bit Ethernet
number and a null terminator.
.sp
.LP
The function \fBether_ntohost()\fR maps an Ethernet number (pointed to by
\fIe\fR) to its associated hostname.  The string pointed to by hostname must be
long enough to hold the hostname and a \fINULL\fR character.  The function
returns zero upon success and non-zero upon failure.  Inversely, the function
\fBether_hostton()\fR maps a hostname string to its corresponding Ethernet
number; the function modifies the Ethernet number pointed to by \fIe\fR. The
function also returns zero upon success and non-zero upon failure. In order to
do the mapping, both these functions may lookup one or more of the following
sources: the ethers file and the \fBNIS\fR maps \fBethers.byname\fR and
\fBethers.byaddr\fR. The sources and
their lookup order are specified in the \fB/etc/nsswitch.conf\fR file. See
\fBnsswitch.conf\fR(5) for details.
.sp
.LP
The function \fBether_line()\fR scans a line, pointed to by \fIl\fR, and sets
the hostname and the Ethernet number, pointed to by \fIe\fR. The string pointed
to by hostname must be long enough to hold the hostname and a \fINULL\fR
character.  The function returns zero upon success and non-zero upon failure.
The format of the scanned line is described by \fBethers\fR(5).
.SH FILES
.ne 2
.na
\fB\fB/etc/ethers\fR\fR
.ad
.RS 22n
Ethernet address to hostname database or domain
.RE

.sp
.ne 2
.na
\fB\fB/etc/nsswitch.conf\fR\fR
.ad
.RS 22n
configuration file for the name service switch
.RE

.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.BR ethers (5),
.BR nsswitch.conf (5),
.BR attributes (7)