[apple/network_cmds.git] / arp.tproj / arp4.4

.\" Copyright (c) 1985, 1986, 1988, 1994
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)arp4.4	6.5 (Berkeley) 4/18/94
.\"
.Dd April 18, 1994
.Dt ARP 4
.Os BSD 4
.Sh NAME
.Nm arp
.Nd Address Resolution Protocol
.Sh SYNOPSIS
.Em "pseudo-device ether"
.Sh DESCRIPTION
The Address Resolution Protocol (ARP) is a protocol used to dynamically
map between Internet host addresses and 10Mb/s Ethernet addresses.
It is used by all the 10Mb/s Ethernet interface drivers.
It is not specific to Internet protocols or to 10Mb/s Ethernet,
but this implementation currently supports only that combination.
.Pp
ARP caches Internet-Ethernet address mappings. 
When an interface requests a mapping for an address not in the cache,
ARP queues the message which requires the mapping and broadcasts
a message on the associated network requesting the address mapping.
If a response is provided, the new mapping is cached and any pending
message is transmitted.
ARP will queue at most one packet while waiting for a response to a
mapping request;
only the most recently ``transmitted'' packet is kept.
If the target host does not respond after several requests,
the host is considered to be down for a short period (normally 20 seconds),
allowing an error to be returned to transmission attempts during this
interval.
The error is
.Li EHOSTDOWN
for a non-responding destination host, and
.Li EHOSTUNREACH
for a non-responding router.
.Pp
The ARP cache is stored in the system routing table as
dynamically-created host routes.
The route to a directly-attached Ethernet network is installed as a
.Dq cloning
route (one with the
.Li RTF_CLONING
flag set),
causing routes to individual hosts on that network to be created on
demand.
These routes time out periodically (normally 20 minutes after validated;
entries are not validated when not in use).
An entry for a host which is not responding is a
.Dq reject
route (one with the
.Li RTF_REJECT
flag set).
.Pp
ARP entries may be added, deleted or changed with the
.Xr arp 8
utility.
Manually-added entries may be temporary or permanent,
and may be
.Dq published ,
in which case the system will respond to ARP requests for that host
as if it were the target of the request.
.Pp
In the past,
ARP was used to negotiate the use of a trailer encapsulation.
This is no longer supported.
.Pp
ARP watches passively for hosts impersonating the local host (i.e. a host
which responds to an ARP mapping request for the local host's address).
.Sh DIAGNOSTICS
.Em "duplicate IP address %x!! sent from ethernet address: %x:%x:%x:%x:%x:%x."
ARP has discovered another host on the local network which responds to
mapping requests for its own Internet address with a different Ethernet
address, generally indicating that two hosts are attempting to use the
same Internet address.
.Sh SEE ALSO
.Xr inet 4 ,
.Xr route 4 ,
.Xr arp 8 ,
.Xr ifconfig 8 ,
.Xr route 8
.sp
.Rs
.%A Plummer, D.
.%B "An Ethernet Address Resolution Protocol"
.%T RFC826
.Re
.Rs
.%A Leffler, S.J.
.%A Karels, M.J.
.%B "Trailer Encapsulations
.%T RFC893
.Re
Commit	Line	Data
b7080c8e A	1	.\" Copyright (c) 1985, 1986, 1988, 1994
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" Redistribution and use in source and binary forms, with or without
	5	.\" modification, are permitted provided that the following conditions
	6	.\" are met:
	7	.\" 1. Redistributions of source code must retain the above copyright
	8	.\" notice, this list of conditions and the following disclaimer.
	9	.\" 2. Redistributions in binary form must reproduce the above copyright
	10	.\" notice, this list of conditions and the following disclaimer in the
	11	.\" documentation and/or other materials provided with the distribution.
	12	.\" 3. All advertising materials mentioning features or use of this software
	13	.\" must display the following acknowledgement:
	14	.\" This product includes software developed by the University of
	15	.\" California, Berkeley and its contributors.
	16	.\" 4. Neither the name of the University nor the names of its contributors
	17	.\" may be used to endorse or promote products derived from this software
	18	.\" without specific prior written permission.
	19	.\"
	20	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	21	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	22	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	23	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	24	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	25	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	26	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	27	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	28	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	29	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	30	.\" SUCH DAMAGE.
	31	.\"
	32	.\" @(#)arp4.4 6.5 (Berkeley) 4/18/94
	33	.\"
	34	.Dd April 18, 1994
	35	.Dt ARP 4
	36	.Os BSD 4
	37	.Sh NAME
	38	.Nm arp
	39	.Nd Address Resolution Protocol
	40	.Sh SYNOPSIS
	41	.Em "pseudo-device ether"
	42	.Sh DESCRIPTION
	43	The Address Resolution Protocol (ARP) is a protocol used to dynamically
	44	map between Internet host addresses and 10Mb/s Ethernet addresses.
	45	It is used by all the 10Mb/s Ethernet interface drivers.
	46	It is not specific to Internet protocols or to 10Mb/s Ethernet,
	47	but this implementation currently supports only that combination.
	48	.Pp
	49	ARP caches Internet-Ethernet address mappings.
	50	When an interface requests a mapping for an address not in the cache,
	51	ARP queues the message which requires the mapping and broadcasts
	52	a message on the associated network requesting the address mapping.
	53	If a response is provided, the new mapping is cached and any pending
	54	message is transmitted.
	55	ARP will queue at most one packet while waiting for a response to a
	56	mapping request;
	57	only the most recently ``transmitted'' packet is kept.
	58	If the target host does not respond after several requests,
	59	the host is considered to be down for a short period (normally 20 seconds),
	60	allowing an error to be returned to transmission attempts during this
	61	interval.
	62	The error is
	63	.Li EHOSTDOWN
	64	for a non-responding destination host, and
65	.Li EHOSTUNREACH
66	for a non-responding router.
67	.Pp
68	The ARP cache is stored in the system routing table as
69	dynamically-created host routes.
70	The route to a directly-attached Ethernet network is installed as a
71	.Dq cloning
72	route (one with the
73	.Li RTF_CLONING
74	flag set),
75	causing routes to individual hosts on that network to be created on
76	demand.
77	These routes time out periodically (normally 20 minutes after validated;
78	entries are not validated when not in use).
79	An entry for a host which is not responding is a
80	.Dq reject
81	route (one with the
82	.Li RTF_REJECT
83	flag set).
84	.Pp
85	ARP entries may be added, deleted or changed with the
86	.Xr arp 8
87	utility.
88	Manually-added entries may be temporary or permanent,
89	and may be
90	.Dq published ,
91	in which case the system will respond to ARP requests for that host
92	as if it were the target of the request.
93	.Pp
94	In the past,
95	ARP was used to negotiate the use of a trailer encapsulation.
96	This is no longer supported.
97	.Pp
98	ARP watches passively for hosts impersonating the local host (i.e. a host
99	which responds to an ARP mapping request for the local host's address).
100	.Sh DIAGNOSTICS
101	.Em "duplicate IP address %x!! sent from ethernet address: %x:%x:%x:%x:%x:%x."
102	ARP has discovered another host on the local network which responds to
103	mapping requests for its own Internet address with a different Ethernet
104	address, generally indicating that two hosts are attempting to use the
105	same Internet address.
106	.Sh SEE ALSO
107	.Xr inet 4 ,
108	.Xr route 4 ,
109	.Xr arp 8 ,
110	.Xr ifconfig 8 ,
111	.Xr route 8
112	.sp
113	.Rs
114	.%A Plummer, D.
115	.%B "An Ethernet Address Resolution Protocol"
116	.%T RFC826
117	.Re
118	.Rs
119	.%A Leffler, S.J.
120	.%A Karels, M.J.
121	.%B "Trailer Encapsulations
122	.%T RFC893
123	.Re