man/man8/ip-route.8.in - maze/iproute2 - Git at Google

 .TH IP\-ROUTE 8 "13 Dec 2012" "iproute2" "Linux"
 .SH "NAME"
 ip-route \- routing table management
 .SH "SYNOPSIS"
 .sp
 .ad l
 .in +8
 .ti -8
 .B ip
 .RI "[ " ip-OPTIONS " ]"
 .B route
 .RI " { " COMMAND " | "
 .BR help " }"
 .sp
 .ti -8

 .ti -8
 .BR "ip route" " { "
 .BR list " | " flush " } "
 .I  SELECTOR

 .ti -8
 .BR "ip route save"
 .I SELECTOR

 .ti -8
 .BR "ip route restore"

 .ti -8
 .B  ip route get
 .IR ADDRESS " [ "
 .BI from " ADDRESS " iif " STRING"
 .RB " ] [ " oif
 .IR STRING " ] [ "
 .B  tos
 .IR TOS " ]"

 .ti -8
 .BR "ip route" " { " add " | " del " | " change " | " append " | "\
 replace " } "
 .I  ROUTE

 .ti -8
 .IR SELECTOR " := "
 .RB "[ " root
 .IR PREFIX " ] [ "
 .B  match
 .IR PREFIX " ] [ "
 .B  exact
 .IR PREFIX " ] [ "
 .B  table
 .IR TABLE_ID " ] [ "
 .B  proto
 .IR RTPROTO " ] [ "
 .B  type
 .IR TYPE " ] [ "
 .B  scope
 .IR SCOPE " ]"

 .ti -8
 .IR ROUTE " := " NODE_SPEC " [ " INFO_SPEC " ]"

 .ti -8
 .IR NODE_SPEC " := [ " TYPE " ] " PREFIX " ["
 .B  tos
 .IR TOS " ] [ "
 .B  table
 .IR TABLE_ID " ] [ "
 .B  proto
 .IR RTPROTO " ] [ "
 .B  scope
 .IR SCOPE " ] [ "
 .B  metric
 .IR METRIC " ]"

 .ti -8
 .IR INFO_SPEC " := " "NH OPTIONS FLAGS" " ["
 .B  nexthop
 .IR NH " ] ..."

 .ti -8
 .IR NH " := [ "
 .B  via
 .IR ADDRESS " ] [ "
 .B  dev
 .IR STRING " ] [ "
 .B  weight
 .IR NUMBER " ] " NHFLAGS

 .ti -8
 .IR OPTIONS " := " FLAGS " [ "
 .B  mtu
 .IR NUMBER " ] [ "
 .B  advmss
 .IR NUMBER " ] [ "
 .B  rtt
 .IR TIME " ] [ "
 .B  rttvar
 .IR TIME " ] [ "
 .B  reordering
 .IR NUMBER " ] [ "
 .B  window
 .IR NUMBER " ] [ "
 .B  cwnd
 .IR NUMBER " ] [ "
 .B  ssthresh
 .IR REALM " ] [ "
 .B  realms
 .IR REALM " ] [ "
 .B  rto_min
 .IR TIME " ] [ "
 .B  initcwnd
 .IR NUMBER " ] [ "
 .B  initrwnd
 .IR NUMBER " ] [ "
 .B  quickack
 .IR BOOL " ]"

 .ti -8
 .IR TYPE " := [ "
 .BR unicast " | " local " | " broadcast " | " multicast " | "\
 throw " | " unreachable " | " prohibit " | " blackhole " | " nat " ]"

 .ti -8
 .IR TABLE_ID " := [ "
 .BR local "| " main " | " default " | " all " |"
 .IR NUMBER " ]"

 .ti -8
 .IR SCOPE " := [ "
 .BR host " | " link " | " global " |"
 .IR NUMBER " ]"

 .ti -8
 .IR NHFLAGS " := [ "
 .BR onlink " | " pervasive " ]"

 .ti -8
 .IR RTPROTO " := [ "
 .BR kernel " | " boot " | " static " |"
 .IR NUMBER " ]"


 .SH DESCRIPTION
 .B ip route
 is used to manipulate entries in the kernel routing tables.
 .sp
 .B Route types:

 .in +8
 .B unicast
 - the route entry describes real paths to the destinations covered
 by the route prefix.

 .sp
 .B unreachable
 - these destinations are unreachable.  Packets are discarded and the
 ICMP message
 .I host unreachable
 is generated.
 The local senders get an
 .I EHOSTUNREACH
 error.

 .sp
 .B blackhole
 - these destinations are unreachable.  Packets are discarded silently.
 The local senders get an
 .I EINVAL
 error.

 .sp
 .B prohibit
 - these destinations are unreachable.  Packets are discarded and the
 ICMP message
 .I communication administratively prohibited
 is generated.  The local senders get an
 .I EACCES
 error.

 .sp
 .B local
 - the destinations are assigned to this host.  The packets are looped
 back and delivered locally.

 .sp
 .B broadcast
 - the destinations are broadcast addresses.  The packets are sent as
 link broadcasts.

 .sp
 .B throw
 - a special control route used together with policy rules. If such a
 route is selected, lookup in this table is terminated pretending that
 no route was found.  Without policy routing it is equivalent to the
 absence of the route in the routing table.  The packets are dropped
 and the ICMP message
 .I net unreachable
 is generated.  The local senders get an
 .I ENETUNREACH
 error.

 .sp
 .B nat
 - a special NAT route.  Destinations covered by the prefix
 are considered to be dummy (or external) addresses which require translation
 to real (or internal) ones before forwarding.  The addresses to translate to
 are selected with the attribute
 .BR "via" .
 .B Warning:
 Route NAT is no longer supported in Linux 2.6.

 .sp
 .B anycast
 .RI "- " "not implemented"
 the destinations are
 .I anycast
 addresses assigned to this host.  They are mainly equivalent
 to
 .B local
 with one difference: such addresses are invalid when used
 as the source address of any packet.

 .sp
 .B multicast
 - a special type used for multicast routing.  It is not present in
 normal routing tables.
 .in -8

 .P
 .B Route tables:
 Linux-2.x can pack routes into several routing tables identified
 by a number in the range from 1 to 2^31 or by name from the file
 .B @SYSCONFDIR@/rt_tables
 By default all normal routes are inserted into the
 .B main
 table (ID 254) and the kernel only uses this table when calculating routes.
 Values (0, 253, 254, and 255) are reserved for built-in use.

 .sp
 Actually, one other table always exists, which is invisible but
 even more important.  It is the
 .B local
 table (ID 255).  This table
 consists of routes for local and broadcast addresses.  The kernel maintains
 this table automatically and the administrator usually need not modify it
 or even look at it.

 The multiple routing tables enter the game when
 .I policy routing
 is used.

 .TP
 ip route add
 add new route
 .TP
 ip route change
 change route
 .TP
 ip route replace
 change or add new one
 .RS
 .TP
 .BI to " TYPE PREFIX " (default)
 the destination prefix of the route.  If
 .I TYPE
 is omitted,
 .B ip
 assumes type
 .BR "unicast" .
 Other values of
 .I TYPE
 are listed above.
 .I PREFIX
 is an IP or IPv6 address optionally followed by a slash and the
 prefix length.  If the length of the prefix is missing,
 .B ip
 assumes a full-length host route.  There is also a special
 .I PREFIX
 .B default
 - which is equivalent to IP
 .B 0/0
 or to IPv6
 .BR "::/0" .

 .TP
 .BI tos " TOS"
 .TP
 .BI dsfield " TOS"
 the Type Of Service (TOS) key.  This key has no associated mask and
 the longest match is understood as: First, compare the TOS
 of the route and of the packet.  If they are not equal, then the packet
 may still match a route with a zero TOS.
 .I TOS
 is either an 8 bit hexadecimal number or an identifier
 from
 .BR "@SYSCONFDIR@/rt_dsfield" .

 .TP
 .BI metric " NUMBER"
 .TP
 .BI preference " NUMBER"
 the preference value of the route.
 .I NUMBER
 is an arbitrary 32bit number.

 .TP
 .BI table " TABLEID"
 the table to add this route to.
 .I TABLEID
 may be a number or a string from the file
 .BR "@SYSCONFDIR@/rt_tables" .
 If this parameter is omitted,
 .B ip
 assumes the
 .B main
 table, with the exception of
 .BR local ", " broadcast " and " nat
 routes, which are put into the
 .B local
 table by default.

 .TP
 .BI dev " NAME"
 the output device name.

 .TP
 .BI via " ADDRESS"
 the address of the nexthop router.  Actually, the sense of this field
 depends on the route type.  For normal
 .B unicast
 routes it is either the true next hop router or, if it is a direct
 route installed in BSD compatibility mode, it can be a local address
 of the interface.  For NAT routes it is the first address of the block
 of translated IP destinations.

 .TP
 .BI src " ADDRESS"
 the source address to prefer when sending to the destinations
 covered by the route prefix.

 .TP
 .BI realm " REALMID"
 the realm to which this route is assigned.
 .I REALMID
 may be a number or a string from the file
 .BR "@SYSCONFDIR@/rt_realms" .

 .TP
 .BI mtu " MTU"
 .TP
 .BI "mtu lock" " MTU"
 the MTU along the path to the destination.  If the modifier
 .B lock
 is not used, the MTU may be updated by the kernel due to
 Path MTU Discovery.  If the modifier
 .B lock
 is used, no path MTU discovery will be tried, all packets
 will be sent without the DF bit in IPv4 case or fragmented
 to MTU for IPv6.

 .TP
 .BI window " NUMBER"
 the maximal window for TCP to advertise to these destinations,
 measured in bytes.  It limits maximal data bursts that our TCP
 peers are allowed to send to us.

 .TP
 .BI rtt " TIME"
 the initial RTT ('Round Trip Time') estimate. If no suffix is
 specified the units are raw values passed directly to the
 routing code to maintain compatibility with previous releases.
 Otherwise if a suffix of s, sec or secs is used to specify
 seconds and ms, msec or msecs to specify milliseconds.


 .TP
 .BI rttvar " TIME " "(2.3.15+ only)"
 the initial RTT variance estimate. Values are specified as with
 .BI rtt
 above.

 .TP
 .BI rto_min " TIME " "(2.6.23+ only)"
 the minimum TCP Retransmission TimeOut to use when communicating with this
 destination.  Values are specified as with
 .BI rtt
 above.

 .TP
 .BI ssthresh " NUMBER " "(2.3.15+ only)"
 an estimate for the initial slow start threshold.

 .TP
 .BI cwnd " NUMBER " "(2.3.15+ only)"
 the clamp for congestion window.  It is ignored if the
 .B lock
 flag is not used.

 .TP
 .BI initcwnd " NUMBER " "(2.5.70+ only)"
 the initial congestion window size for connections to this destination.
 Actual window size is this value multiplied by the MSS
 (``Maximal Segment Size'') for same connection. The default is
 zero, meaning to use the values specified in RFC2414.

 .TP
 .BI initrwnd " NUMBER " "(2.6.33+ only)"
 the initial receive window size for connections to this destination.
 Actual window size is this value multiplied by the MSS of the connection.
 The default value is zero, meaning to use Slow Start value.

 .TP
 .BI quickack " BOOL " "(3.11+ only)"
 Enable or disable quick ack for connections to this destination.

 .TP
 .BI advmss " NUMBER " "(2.3.15+ only)"
 the MSS ('Maximal Segment Size') to advertise to these
 destinations when establishing TCP connections.  If it is not given,
 Linux uses a default value calculated from the first hop device MTU.
 (If the path to these destination is asymmetric, this guess may be wrong.)

 .TP
 .BI reordering " NUMBER " "(2.3.15+ only)"
 Maximal reordering on the path to this destination.
 If it is not given, Linux uses the value selected with
 .B sysctl
 variable
 .BR "net/ipv4/tcp_reordering" .

 .TP
 .BI nexthop " NEXTHOP"
 the nexthop of a multipath route.
 .I NEXTHOP
 is a complex value with its own syntax similar to the top level
 argument lists:

 .in +8
 .BI via " ADDRESS"
 - is the nexthop router.
 .sp

 .BI dev " NAME"
 - is the output device.
 .sp

 .BI weight " NUMBER"
 - is a weight for this element of a multipath
 route reflecting its relative bandwidth or quality.
 .in -8

 .TP
 .BI scope " SCOPE_VAL"
 the scope of the destinations covered by the route prefix.
 .I SCOPE_VAL
 may be a number or a string from the file
 .BR "@SYSCONFDIR@/rt_scopes" .
 If this parameter is omitted,
 .B ip
 assumes scope
 .B global
 for all gatewayed
 .B unicast
 routes, scope
 .B link
 for direct
 .BR unicast " and " broadcast
 routes and scope
 .BR host " for " local
 routes.

 .TP
 .BI protocol " RTPROTO"
 the routing protocol identifier of this route.
 .I RTPROTO
 may be a number or a string from the file
 .BR "@SYSCONFDIR@/rt_protos" .
 If the routing protocol ID is not given,
 .B ip assumes protocol
 .B boot
 (i.e. it assumes the route was added by someone who doesn't
 understand what they are doing).  Several protocol values have
 a fixed interpretation.
 Namely:

 .in +8
 .B redirect
 - the route was installed due to an ICMP redirect.
 .sp

 .B kernel
 - the route was installed by the kernel during autoconfiguration.
 .sp

 .B boot
 - the route was installed during the bootup sequence.
 If a routing daemon starts, it will purge all of them.
 .sp

 .B static
 - the route was installed by the administrator
 to override dynamic routing. Routing daemon will respect them
 and, probably, even advertise them to its peers.
 .sp

 .B ra
 - the route was installed by Router Discovery protocol.
 .in -8

 .sp
 The rest of the values are not reserved and the administrator is free
 to assign (or not to assign) protocol tags.

 .TP
 .B onlink
 pretend that the nexthop is directly attached to this link,
 even if it does not match any interface prefix.
 .RE

 .TP
 ip route delete
 delete route
 .RS
 .B ip route del
 has the same arguments as
 .BR "ip route add" ,
 but their semantics are a bit different.

 Key values
 .RB "(" to ", " tos ", " preference " and " table ")"
 select the route to delete.  If optional attributes are present,
 .B ip
 verifies that they coincide with the attributes of the route to delete.
 If no route with the given key and attributes was found,
 .B ip route del
 fails.
 .RE

 .TP
 ip route show
 list routes
 .RS
 the command displays the contents of the routing tables or the route(s)
 selected by some criteria.

 .TP
 .BI to " SELECTOR " (default)
 only select routes from the given range of destinations.
 .I SELECTOR
 consists of an optional modifier
 .RB "(" root ", " match " or " exact ")"
 and a prefix.
 .BI root " PREFIX"
 selects routes with prefixes not shorter than
 .IR PREFIX "."
 F.e.
 .BI root " 0/0"
 selects the entire routing table.
 .BI match " PREFIX"
 selects routes with prefixes not longer than
 .IR PREFIX "."
 F.e.
 .BI match " 10.0/16"
 selects
 .IR 10.0/16 ","
 .IR 10/8 " and " 0/0 ,
 but it does not select
 .IR 10.1/16 " and " 10.0.0/24 .
 And
 .BI exact " PREFIX"
 (or just
 .IR PREFIX ")"
 selects routes with this exact prefix. If neither of these options
 are present,
 .B ip
 assumes
 .BI root " 0/0"
 i.e. it lists the entire table.

 .TP
 .BI tos " TOS"
 .TP
 .BI dsfield " TOS"
 only select routes with the given TOS.

 .TP
 .BI table " TABLEID"
 show the routes from this table(s).  The default setting is to show table
 .BR main "."
 .I TABLEID
 may either be the ID of a real table or one of the special values:
 .sp
 .in +8
 .B all
 - list all of the tables.
 .sp
 .B cache
 - dump the routing cache.
 .in -8

 .TP
 .B cloned
 .TP
 .B cached
 list cloned routes i.e. routes which were dynamically forked from
 other routes because some route attribute (f.e. MTU) was updated.
 Actually, it is equivalent to
 .BR "table cache" "."

 .TP
 .BI from " SELECTOR"
 the same syntax as for
 .BR to ","
 but it binds the source address range rather than destinations.
 Note that the
 .B from
 option only works with cloned routes.

 .TP
 .BI protocol " RTPROTO"
 only list routes of this protocol.

 .TP
 .BI scope " SCOPE_VAL"
 only list routes with this scope.

 .TP
 .BI type " TYPE"
 only list routes of this type.

 .TP
 .BI dev " NAME"
 only list routes going via this device.

 .TP
 .BI via " PREFIX"
 only list routes going via the nexthop routers selected by
 .IR PREFIX "."

 .TP
 .BI src " PREFIX"
 only list routes with preferred source addresses selected
 by
 .IR PREFIX "."

 .TP
 .BI realm " REALMID"
 .TP
 .BI realms " FROMREALM/TOREALM"
 only list routes with these realms.
 .RE

 .TP
 ip route flush
 flush routing tables
 .RS
 this command flushes routes selected by some criteria.

 .sp
 The arguments have the same syntax and semantics as the arguments of
 .BR "ip route show" ,
 but routing tables are not listed but purged.  The only difference is
 the default action:
 .B show
 dumps all the IP main routing table but
 .B flush
 prints the helper page.

 .sp
 With the
 .B -statistics
 option, the command becomes verbose. It prints out the number of
 deleted routes and the number of rounds made to flush the routing
 table. If the option is given
 twice,
 .B ip route flush
 also dumps all the deleted routes in the format described in the
 previous subsection.
 .RE

 .TP
 ip route get
 get a single route
 .RS
 this command gets a single route to a destination and prints its
 contents exactly as the kernel sees it.

 .TP
 .BI to " ADDRESS " (default)
 the destination address.

 .TP
 .BI from " ADDRESS"
 the source address.

 .TP
 .BI tos " TOS"
 .TP
 .BI dsfield " TOS"
 the Type Of Service.

 .TP
 .BI iif " NAME"
 the device from which this packet is expected to arrive.

 .TP
 .BI oif " NAME"
 force the output device on which this packet will be routed.

 .TP
 .B connected
 if no source address
 .RB "(option " from ")"
 was given, relookup the route with the source set to the preferred
 address received from the first lookup.
 If policy routing is used, it may be a different route.

 .P
 Note that this operation is not equivalent to
 .BR "ip route show" .
 .B show
 shows existing routes.
 .B get
 resolves them and creates new clones if necessary.  Essentially,
 .B get
 is equivalent to sending a packet along this path.
 If the
 .B iif
 argument is not given, the kernel creates a route
 to output packets towards the requested destination.
 This is equivalent to pinging the destination
 with a subsequent
 .BR "ip route ls cache" ,
 however, no packets are actually sent.  With the
 .B iif
 argument, the kernel pretends that a packet arrived from this interface
 and searches for a path to forward the packet.
 .RE

 .TP
 ip route save
 save routing table information to stdout
 .RS
 This command behaves like
 .BR "ip route show"
 except that the output is raw data suitable for passing to
 .BR "ip route restore" .
 .RE

 .TP
 ip route restore
 restore routing table information from stdin
 .RS
 This command expects to read a data stream as returned from
 .BR "ip route save" .
 It will attempt to restore the routing table information exactly as
 it was at the time of the save, so any translation of information
 in the stream (such as device indexes) must be done first.  Any existing
 routes are left unchanged.  Any routes specified in the data stream that
 already exist in the table will be ignored.
 .RE

 .SH EXAMPLES
 .PP
 ip ro
 .RS 4
 Show all route entries in the kernel.
 .RE
 .PP
 ip route add default via 192.168.1.1 dev eth0
 .RS 4
 Adds a default route (for all addresses) via the local gateway 192.168.1.1 that can
 be reached on device eth0.
 .RE

 .SH SEE ALSO
 .br
 .BR ip (8)

 .SH AUTHOR
 Original Manpage by Michail Litvak <mci@owl.openwall.com>
	.TH IP\-ROUTE 8 "13 Dec 2012" "iproute2" "Linux"
	.SH "NAME"
	ip-route \- routing table management
	.SH "SYNOPSIS"
	.sp
	.ad l
	.in +8
	.ti -8
	.B ip
	.RI "[ " ip-OPTIONS " ]"
	.B route
	.RI " { " COMMAND " \| "
	.BR help " }"
	.sp
	.ti -8

	.ti -8
	.BR "ip route" " { "
	.BR list " \| " flush " } "
	.I SELECTOR

	.ti -8
	.BR "ip route save"
	.I SELECTOR

	.ti -8
	.BR "ip route restore"

	.ti -8
	.B ip route get
	.IR ADDRESS " [ "
	.BI from " ADDRESS " iif " STRING"
	.RB " ] [ " oif
	.IR STRING " ] [ "
	.B tos
	.IR TOS " ]"

	.ti -8
	.BR "ip route" " { " add " \| " del " \| " change " \| " append " \| "\
	replace " } "
	.I ROUTE

	.ti -8
	.IR SELECTOR " := "
	.RB "[ " root
	.IR PREFIX " ] [ "
	.B match
	.IR PREFIX " ] [ "
	.B exact
	.IR PREFIX " ] [ "
	.B table
	.IR TABLE_ID " ] [ "
	.B proto
	.IR RTPROTO " ] [ "
	.B type
	.IR TYPE " ] [ "
	.B scope
	.IR SCOPE " ]"

	.ti -8
	.IR ROUTE " := " NODE_SPEC " [ " INFO_SPEC " ]"

	.ti -8
	.IR NODE_SPEC " := [ " TYPE " ] " PREFIX " ["
	.B tos
	.IR TOS " ] [ "
	.B table
	.IR TABLE_ID " ] [ "
	.B proto
	.IR RTPROTO " ] [ "
	.B scope
	.IR SCOPE " ] [ "
	.B metric
	.IR METRIC " ]"

	.ti -8
	.IR INFO_SPEC " := " "NH OPTIONS FLAGS" " ["
	.B nexthop
	.IR NH " ] ..."

	.ti -8
	.IR NH " := [ "
	.B via
	.IR ADDRESS " ] [ "
	.B dev
	.IR STRING " ] [ "
	.B weight
	.IR NUMBER " ] " NHFLAGS

	.ti -8
	.IR OPTIONS " := " FLAGS " [ "
	.B mtu
	.IR NUMBER " ] [ "
	.B advmss
	.IR NUMBER " ] [ "
	.B rtt
	.IR TIME " ] [ "
	.B rttvar
	.IR TIME " ] [ "
	.B reordering
	.IR NUMBER " ] [ "
	.B window
	.IR NUMBER " ] [ "
	.B cwnd
	.IR NUMBER " ] [ "
	.B ssthresh
	.IR REALM " ] [ "
	.B realms
	.IR REALM " ] [ "
	.B rto_min
	.IR TIME " ] [ "
	.B initcwnd
	.IR NUMBER " ] [ "
	.B initrwnd
	.IR NUMBER " ] [ "
	.B quickack
	.IR BOOL " ]"

	.ti -8
	.IR TYPE " := [ "
	.BR unicast " \| " local " \| " broadcast " \| " multicast " \| "\
	throw " \| " unreachable " \| " prohibit " \| " blackhole " \| " nat " ]"

	.ti -8
	.IR TABLE_ID " := [ "
	.BR local "\| " main " \| " default " \| " all " \|"
	.IR NUMBER " ]"

	.ti -8
	.IR SCOPE " := [ "
	.BR host " \| " link " \| " global " \|"
	.IR NUMBER " ]"

	.ti -8
	.IR NHFLAGS " := [ "
	.BR onlink " \| " pervasive " ]"

	.ti -8
	.IR RTPROTO " := [ "
	.BR kernel " \| " boot " \| " static " \|"
	.IR NUMBER " ]"


	.SH DESCRIPTION
	.B ip route
	is used to manipulate entries in the kernel routing tables.
	.sp
	.B Route types:

	.in +8
	.B unicast
	- the route entry describes real paths to the destinations covered
	by the route prefix.

	.sp
	.B unreachable
	- these destinations are unreachable. Packets are discarded and the
	ICMP message
	.I host unreachable
	is generated.
	The local senders get an
	.I EHOSTUNREACH
	error.

	.sp
	.B blackhole
	- these destinations are unreachable. Packets are discarded silently.
	The local senders get an
	.I EINVAL
	error.

	.sp
	.B prohibit
	- these destinations are unreachable. Packets are discarded and the
	ICMP message
	.I communication administratively prohibited
	is generated. The local senders get an
	.I EACCES
	error.

	.sp
	.B local
	- the destinations are assigned to this host. The packets are looped
	back and delivered locally.

	.sp
	.B broadcast
	- the destinations are broadcast addresses. The packets are sent as
	link broadcasts.

	.sp
	.B throw
	- a special control route used together with policy rules. If such a
	route is selected, lookup in this table is terminated pretending that
	no route was found. Without policy routing it is equivalent to the
	absence of the route in the routing table. The packets are dropped
	and the ICMP message
	.I net unreachable
	is generated. The local senders get an
	.I ENETUNREACH
	error.

	.sp
	.B nat
	- a special NAT route. Destinations covered by the prefix
	are considered to be dummy (or external) addresses which require translation
	to real (or internal) ones before forwarding. The addresses to translate to
	are selected with the attribute
	.BR "via" .
	.B Warning:
	Route NAT is no longer supported in Linux 2.6.

	.sp
	.B anycast
	.RI "- " "not implemented"
	the destinations are
	.I anycast
	addresses assigned to this host. They are mainly equivalent
	to
	.B local
	with one difference: such addresses are invalid when used
	as the source address of any packet.

	.sp
	.B multicast
	- a special type used for multicast routing. It is not present in
	normal routing tables.
	.in -8

	.P
	.B Route tables:
	Linux-2.x can pack routes into several routing tables identified
	by a number in the range from 1 to 2^31 or by name from the file
	.B @SYSCONFDIR@/rt_tables
	By default all normal routes are inserted into the
	.B main
	table (ID 254) and the kernel only uses this table when calculating routes.
	Values (0, 253, 254, and 255) are reserved for built-in use.

	.sp
	Actually, one other table always exists, which is invisible but
	even more important. It is the
	.B local
	table (ID 255). This table
	consists of routes for local and broadcast addresses. The kernel maintains
	this table automatically and the administrator usually need not modify it
	or even look at it.

	The multiple routing tables enter the game when
	.I policy routing
	is used.

	.TP
	ip route add
	add new route
	.TP
	ip route change
	change route
	.TP
	ip route replace
	change or add new one
	.RS
	.TP
	.BI to " TYPE PREFIX " (default)
	the destination prefix of the route. If
	.I TYPE
	is omitted,
	.B ip
	assumes type
	.BR "unicast" .
	Other values of
	.I TYPE
	are listed above.
	.I PREFIX
	is an IP or IPv6 address optionally followed by a slash and the
	prefix length. If the length of the prefix is missing,
	.B ip
	assumes a full-length host route. There is also a special
	.I PREFIX
	.B default
	- which is equivalent to IP
	.B 0/0
	or to IPv6
	.BR "::/0" .

	.TP
	.BI tos " TOS"
	.TP
	.BI dsfield " TOS"
	the Type Of Service (TOS) key. This key has no associated mask and
	the longest match is understood as: First, compare the TOS
	of the route and of the packet. If they are not equal, then the packet
	may still match a route with a zero TOS.
	.I TOS
	is either an 8 bit hexadecimal number or an identifier
	from
	.BR "@SYSCONFDIR@/rt_dsfield" .

	.TP
	.BI metric " NUMBER"
	.TP
	.BI preference " NUMBER"
	the preference value of the route.
	.I NUMBER
	is an arbitrary 32bit number.

	.TP
	.BI table " TABLEID"
	the table to add this route to.
	.I TABLEID
	may be a number or a string from the file
	.BR "@SYSCONFDIR@/rt_tables" .
	If this parameter is omitted,
	.B ip
	assumes the
	.B main
	table, with the exception of
	.BR local ", " broadcast " and " nat
	routes, which are put into the
	.B local
	table by default.

	.TP
	.BI dev " NAME"
	the output device name.

	.TP
	.BI via " ADDRESS"
	the address of the nexthop router. Actually, the sense of this field
	depends on the route type. For normal
	.B unicast
	routes it is either the true next hop router or, if it is a direct
	route installed in BSD compatibility mode, it can be a local address
	of the interface. For NAT routes it is the first address of the block
	of translated IP destinations.

	.TP
	.BI src " ADDRESS"
	the source address to prefer when sending to the destinations
	covered by the route prefix.

	.TP
	.BI realm " REALMID"
	the realm to which this route is assigned.
	.I REALMID
	may be a number or a string from the file
	.BR "@SYSCONFDIR@/rt_realms" .

	.TP
	.BI mtu " MTU"
	.TP
	.BI "mtu lock" " MTU"
	the MTU along the path to the destination. If the modifier
	.B lock
	is not used, the MTU may be updated by the kernel due to
	Path MTU Discovery. If the modifier
	.B lock
	is used, no path MTU discovery will be tried, all packets
	will be sent without the DF bit in IPv4 case or fragmented
	to MTU for IPv6.

	.TP
	.BI window " NUMBER"
	the maximal window for TCP to advertise to these destinations,
	measured in bytes. It limits maximal data bursts that our TCP
	peers are allowed to send to us.

	.TP
	.BI rtt " TIME"
	the initial RTT ('Round Trip Time') estimate. If no suffix is
	specified the units are raw values passed directly to the
	routing code to maintain compatibility with previous releases.
	Otherwise if a suffix of s, sec or secs is used to specify
	seconds and ms, msec or msecs to specify milliseconds.


	.TP
	.BI rttvar " TIME " "(2.3.15+ only)"
	the initial RTT variance estimate. Values are specified as with
	.BI rtt
	above.

	.TP
	.BI rto_min " TIME " "(2.6.23+ only)"
	the minimum TCP Retransmission TimeOut to use when communicating with this
	destination. Values are specified as with
	.BI rtt
	above.

	.TP
	.BI ssthresh " NUMBER " "(2.3.15+ only)"
	an estimate for the initial slow start threshold.

	.TP
	.BI cwnd " NUMBER " "(2.3.15+ only)"
	the clamp for congestion window. It is ignored if the
	.B lock
	flag is not used.

	.TP
	.BI initcwnd " NUMBER " "(2.5.70+ only)"
	the initial congestion window size for connections to this destination.
	Actual window size is this value multiplied by the MSS
	(``Maximal Segment Size'') for same connection. The default is
	zero, meaning to use the values specified in RFC2414.

	.TP
	.BI initrwnd " NUMBER " "(2.6.33+ only)"
	the initial receive window size for connections to this destination.
	Actual window size is this value multiplied by the MSS of the connection.
	The default value is zero, meaning to use Slow Start value.

	.TP
	.BI quickack " BOOL " "(3.11+ only)"
	Enable or disable quick ack for connections to this destination.

	.TP
	.BI advmss " NUMBER " "(2.3.15+ only)"
	the MSS ('Maximal Segment Size') to advertise to these
	destinations when establishing TCP connections. If it is not given,
	Linux uses a default value calculated from the first hop device MTU.
	(If the path to these destination is asymmetric, this guess may be wrong.)

	.TP
	.BI reordering " NUMBER " "(2.3.15+ only)"
	Maximal reordering on the path to this destination.
	If it is not given, Linux uses the value selected with
	.B sysctl
	variable
	.BR "net/ipv4/tcp_reordering" .

	.TP
	.BI nexthop " NEXTHOP"
	the nexthop of a multipath route.
	.I NEXTHOP
	is a complex value with its own syntax similar to the top level
	argument lists:

	.in +8
	.BI via " ADDRESS"
	- is the nexthop router.
	.sp

	.BI dev " NAME"
	- is the output device.
	.sp

	.BI weight " NUMBER"
	- is a weight for this element of a multipath
	route reflecting its relative bandwidth or quality.
	.in -8

	.TP
	.BI scope " SCOPE_VAL"
	the scope of the destinations covered by the route prefix.
	.I SCOPE_VAL
	may be a number or a string from the file
	.BR "@SYSCONFDIR@/rt_scopes" .
	If this parameter is omitted,
	.B ip
	assumes scope
	.B global
	for all gatewayed
	.B unicast
	routes, scope
	.B link
	for direct
	.BR unicast " and " broadcast
	routes and scope
	.BR host " for " local
	routes.

	.TP
	.BI protocol " RTPROTO"
	the routing protocol identifier of this route.
	.I RTPROTO
	may be a number or a string from the file
	.BR "@SYSCONFDIR@/rt_protos" .
	If the routing protocol ID is not given,
	.B ip assumes protocol
	.B boot
	(i.e. it assumes the route was added by someone who doesn't
	understand what they are doing). Several protocol values have
	a fixed interpretation.
	Namely:

	.in +8
	.B redirect
	- the route was installed due to an ICMP redirect.
	.sp

	.B kernel
	- the route was installed by the kernel during autoconfiguration.
	.sp

	.B boot
	- the route was installed during the bootup sequence.
	If a routing daemon starts, it will purge all of them.
	.sp

	.B static
	- the route was installed by the administrator
	to override dynamic routing. Routing daemon will respect them
	and, probably, even advertise them to its peers.
	.sp

	.B ra
	- the route was installed by Router Discovery protocol.
	.in -8

	.sp
	The rest of the values are not reserved and the administrator is free
	to assign (or not to assign) protocol tags.

	.TP
	.B onlink
	pretend that the nexthop is directly attached to this link,
	even if it does not match any interface prefix.
	.RE

	.TP
	ip route delete
	delete route
	.RS
	.B ip route del
	has the same arguments as
	.BR "ip route add" ,
	but their semantics are a bit different.

	Key values
	.RB "(" to ", " tos ", " preference " and " table ")"
	select the route to delete. If optional attributes are present,
	.B ip
	verifies that they coincide with the attributes of the route to delete.
	If no route with the given key and attributes was found,
	.B ip route del
	fails.
	.RE

	.TP
	ip route show
	list routes
	.RS
	the command displays the contents of the routing tables or the route(s)
	selected by some criteria.

	.TP
	.BI to " SELECTOR " (default)
	only select routes from the given range of destinations.
	.I SELECTOR
	consists of an optional modifier
	.RB "(" root ", " match " or " exact ")"
	and a prefix.
	.BI root " PREFIX"
	selects routes with prefixes not shorter than
	.IR PREFIX "."
	F.e.
	.BI root " 0/0"
	selects the entire routing table.
	.BI match " PREFIX"
	selects routes with prefixes not longer than
	.IR PREFIX "."
	F.e.
	.BI match " 10.0/16"
	selects
	.IR 10.0/16 ","
	.IR 10/8 " and " 0/0 ,
	but it does not select
	.IR 10.1/16 " and " 10.0.0/24 .
	And
	.BI exact " PREFIX"
	(or just
	.IR PREFIX ")"
	selects routes with this exact prefix. If neither of these options
	are present,
	.B ip
	assumes
	.BI root " 0/0"
	i.e. it lists the entire table.

	.TP
	.BI tos " TOS"
	.TP
	.BI dsfield " TOS"
	only select routes with the given TOS.

	.TP
	.BI table " TABLEID"
	show the routes from this table(s). The default setting is to show table
	.BR main "."
	.I TABLEID
	may either be the ID of a real table or one of the special values:
	.sp
	.in +8
	.B all
	- list all of the tables.
	.sp
	.B cache
	- dump the routing cache.
	.in -8

	.TP
	.B cloned
	.TP
	.B cached
	list cloned routes i.e. routes which were dynamically forked from
	other routes because some route attribute (f.e. MTU) was updated.
	Actually, it is equivalent to
	.BR "table cache" "."

	.TP
	.BI from " SELECTOR"
	the same syntax as for
	.BR to ","
	but it binds the source address range rather than destinations.
	Note that the
	.B from
	option only works with cloned routes.

	.TP
	.BI protocol " RTPROTO"
	only list routes of this protocol.

	.TP
	.BI scope " SCOPE_VAL"
	only list routes with this scope.

	.TP
	.BI type " TYPE"
	only list routes of this type.

	.TP
	.BI dev " NAME"
	only list routes going via this device.

	.TP
	.BI via " PREFIX"
	only list routes going via the nexthop routers selected by
	.IR PREFIX "."

	.TP
	.BI src " PREFIX"
	only list routes with preferred source addresses selected
	by
	.IR PREFIX "."

	.TP
	.BI realm " REALMID"
	.TP
	.BI realms " FROMREALM/TOREALM"
	only list routes with these realms.
	.RE

	.TP
	ip route flush
	flush routing tables
	.RS
	this command flushes routes selected by some criteria.

	.sp
	The arguments have the same syntax and semantics as the arguments of
	.BR "ip route show" ,
	but routing tables are not listed but purged. The only difference is
	the default action:
	.B show
	dumps all the IP main routing table but
	.B flush
	prints the helper page.

	.sp
	With the
	.B -statistics
	option, the command becomes verbose. It prints out the number of
	deleted routes and the number of rounds made to flush the routing
	table. If the option is given
	twice,
	.B ip route flush
	also dumps all the deleted routes in the format described in the
	previous subsection.
	.RE

	.TP
	ip route get
	get a single route
	.RS
	this command gets a single route to a destination and prints its
	contents exactly as the kernel sees it.

	.TP
	.BI to " ADDRESS " (default)
	the destination address.

	.TP
	.BI from " ADDRESS"
	the source address.

	.TP
	.BI tos " TOS"
	.TP
	.BI dsfield " TOS"
	the Type Of Service.

	.TP
	.BI iif " NAME"
	the device from which this packet is expected to arrive.

	.TP
	.BI oif " NAME"
	force the output device on which this packet will be routed.

	.TP
	.B connected
	if no source address
	.RB "(option " from ")"
	was given, relookup the route with the source set to the preferred
	address received from the first lookup.
	If policy routing is used, it may be a different route.

	.P
	Note that this operation is not equivalent to
	.BR "ip route show" .
	.B show
	shows existing routes.
	.B get
	resolves them and creates new clones if necessary. Essentially,
	.B get
	is equivalent to sending a packet along this path.
	If the
	.B iif
	argument is not given, the kernel creates a route
	to output packets towards the requested destination.
	This is equivalent to pinging the destination
	with a subsequent
	.BR "ip route ls cache" ,
	however, no packets are actually sent. With the
	.B iif
	argument, the kernel pretends that a packet arrived from this interface
	and searches for a path to forward the packet.
	.RE

	.TP
	ip route save
	save routing table information to stdout
	.RS
	This command behaves like
	.BR "ip route show"
	except that the output is raw data suitable for passing to
	.BR "ip route restore" .
	.RE

	.TP
	ip route restore
	restore routing table information from stdin
	.RS
	This command expects to read a data stream as returned from
	.BR "ip route save" .
	It will attempt to restore the routing table information exactly as
	it was at the time of the save, so any translation of information
	in the stream (such as device indexes) must be done first. Any existing
	routes are left unchanged. Any routes specified in the data stream that
	already exist in the table will be ignored.
	.RE

	.SH EXAMPLES
	.PP
	ip ro
	.RS 4
	Show all route entries in the kernel.
	.RE
	.PP
	ip route add default via 192.168.1.1 dev eth0
	.RS 4
	Adds a default route (for all addresses) via the local gateway 192.168.1.1 that can
	be reached on device eth0.
	.RE

	.SH SEE ALSO
	.br
	.BR ip (8)

	.SH AUTHOR
	Original Manpage by Michail Litvak <mci@owl.openwall.com>