.\"
.\" FIXME: Document IP_MINTTL, added in Linux 2.6.34
.\"
-.TH IP 7 2010-10-13 "Linux" "Linux Programmer's Manual"
+.TH IP 7 2011-09-22 "Linux" "Linux Programmer's Manual"
.SH NAME
ip \- Linux IPv4 protocol implementation
.SH SYNOPSIS
An IP socket is created by calling the
.BR socket (2)
function as
-.BR "socket(AF_INET, socket_type, protocol)" .
+.BI "socket(AF_INET, " socket_type ", " protocol ) \fR.
Valid socket types are
.B SOCK_STREAM
to open a
.I struct in_addr
contains the host interface address in network byte order.
.I in_addr
-should be assigned one of the INADDR_* values (e.g.,
+should be assigned one of the
+.BR INADDR_*
+values (e.g.,
.BR INADDR_ANY )
or set using the
.BR inet_aton (3),
structure similar to
.BR IP_ADD_MEMBERSHIP .
.TP
+.BR IP_FREEBIND " (since Linux 2.4)"
+.\" Precisely: 2.4.0-test10
+If enabled, this boolean option allows binding to an IP address
+that is nonlocal or does not (yet) exist.
+This permits listening on a socket,
+without requiring the underlying network interface or the
+specified dynamic IP address to be up at the time that
+the application is trying to bind to it.
+This option is the per-socket equivalent of the
+.IR ip_nonlocal_bind
+.I /proc
+interface described below.
+.TP
.BR IP_HDRINCL " (since Linux 2.0)"
If enabled,
the user supplies an IP header in front of the user data.
and
.B IP_TOS
are ignored.
-.TP
-.BR IP_FREEBIND " (since Linux 2.4)"
-.\" Precisely: 2.4.0-test10
-If enabled, this boolean option allows binding to an IP address
-that is nonlocal or does not (yet) exist.
-This permits listening on a socket,
-without requiring the underlying network interface or the
-specified dynamic IP address to be up at the time that
-the application is trying to bind to it.
-This option is the per-socket equivalent of the
-.IR ip_nonlocal_bind
-.I /proc
-interface described below.
.\"
.\" FIXME Document IP_IPSEC_POLICY
.\" Since Linux 2.5.47
.\" Precisely: 2.1.124
Set or receive the Path MTU Discovery setting for a socket.
When enabled, Linux will perform Path MTU Discovery
-as defined in RFC\ 1191
-on this socket.
-The don't-fragment flag is set on all outgoing datagrams.
-The system-wide default is controlled by the
-.I /proc/sys/net/ipv4/ip_no_pmtu_disc
-file for
+as defined in RFC\ 1191 on
.B SOCK_STREAM
-sockets, and disabled on all others.
+sockets.
For
.RB non- SOCK_STREAM
-sockets, it is the user's responsibility to packetize the data
-in MTU sized chunks and to do the retransmits if necessary.
-The kernel will reject packets that are bigger than the known
-path MTU if this flag is set (with
-.B EMSGSIZE
-).
+sockets,
+.B IP_PMTUDISC_DO
+forces the don't-fragment flag to be set on all outgoing packets.
+It is the user's responsibility to packetize the data
+in MTU-sized chunks and to do the retransmits if necessary.
+The kernel will reject (with
+.BR EMSGSIZE )
+datagrams that are bigger than the known path MTU.
+.B IP_PMTUDISC_WANT
+will fragment a datagram if needed according to the path MTU,
+or will set the don't-fragment flag otherwise.
+
+The system-wide default can be toggled between
+.B IP_PMTUDISC_WANT
+and
+.B IP_PMTUDISC_DONT
+by writing (respectively, zero and nonzero values) to the
+.I /proc/sys/net/ipv4/ip_no_pmtu_disc
+file.
+
.TS
tab(:);
c l
l l.
-Path MTU discovery flags:Meaning
+Path MTU discovery value:Meaning
IP_PMTUDISC_WANT:Use per-route settings.
IP_PMTUDISC_DONT:Never do Path MTU Discovery.
IP_PMTUDISC_DO:Always do Path MTU Discovery.
.BR connect (2),
the currently known path MTU can be retrieved conveniently using the
.B IP_MTU
-socket option (e.g., after a
+socket option (e.g., after an
.B EMSGSIZE
error occurred).
-It may change over time.
+The path MTU may change over time.
For connectionless sockets with many destinations,
the new MTU for a given destination can also be accessed using the
error queue (see
.\" commit 2c7946a7bf45ae86736ab3b43d0085e43947945c
.\" Author: Catherine Zhang <cxzhang@watson.ibm.com>
.TP
-.BR IP_RECVORIGDSTADDR " (since Linux 2.6.29)"
-.\" FIXME: Document IP_ORIGDSTADDR+IP_RECVORIGDSTADDR, added in Linux 2.6.29
-.\" commit e8b2dfe9b4501ed0047459b2756ba26e5a940a69
-This boolean option enables the
-.B IP_ORIGDSTADDR
-ancillary message in
-.BR recvmsg (2),
-in which the kernel returns the original destination address
-of the datagram being received.
-The ancillary message contains a
-.IR "struct sockaddr_in" .
-.TP
.BR IP_PKTINFO " (since Linux 2.2)"
.\" Precisely: 2.1.68
Pass an
macro.
The
.I sin_family
-field of the SO_EE_OFFENDER address is
+field of the
+.B SO_EE_OFFENDER
+address is
.B AF_UNSPEC
when the source was unknown.
When the error originated from the network, all IP options
-.RI ( IP_OPTIONS ", " IP_TTL ", "
+.RB ( IP_OPTIONS ", " IP_TTL ", "
etc.) enabled on the socket and contained in the
error packet are passed as control messages.
The payload of the packet causing the error is returned as normal payload.
.B SOCK_STREAM
sockets.
.TP
+.BR IP_RECVORIGDSTADDR " (since Linux 2.6.29)"
+.\" commit e8b2dfe9b4501ed0047459b2756ba26e5a940a69
+This boolean option enables the
+.B IP_ORIGDSTADDR
+ancillary message in
+.BR recvmsg (2),
+in which the kernel returns the original destination address
+of the datagram being received.
+The ancillary message contains a
+.IR "struct sockaddr_in" .
+.TP
.BR IP_RECVTOS " (since Linux 2.2)"
.\" Precisely: 2.1.68
If enabled the
.\" Author: KOVACS Krisztian <hidden@sch.bme.hu>
.\" http://lwn.net/Articles/252545/
.TP
-.BR IP_TTL " (since Linux 2.6.24)"
+.BR IP_TRANSPARENT " (since Linux 2.6.24)"
.\" commit f5715aea4564f233767ea1d944b2637a5fd7cd2e
.\" This patch introduces the IP_TRANSPARENT socket option: enabling that
.\" will make the IPv4 routing omit the non-local source address check on
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