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Linux ip command

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ip is a new, unique for Linux utility that is a part of iproute2 package. It was written by Alexey Kuznetsov. It designed to replace old Unix utilities ifconfig, netstat and route.

So far it did not have much success in this role. But it provides some additional capabilities.

One of the most important is the ability to setup "policy routing" (with the exception of TOS/QoS: tc utility performs those functions). For example

Display routing table(s)
ip route

Provide IP info / gateway to the new corporate table.

ip route add 192.168.0.0/24 dev eth0 src 192.168.0.99 table corporate
ip route add default via 192.168.0.1 dev eth0 table corporate

Create IP rules to handle inbound / outbound traffic:

ip rule add from 192.168.0.99/32 table corporate
ip rule add to 192.168.0.99/32 table corporate

Syntax

ip [ OPTIONS ] OBJECT { COMMAND | help }

OPTIONS := { -V[ersion] | -s[tatistics] | -r[esolve] | -f[amily] { inet | inet6 | ipx | dnet | link } | -o[neline] }

OBJECT := { link | addr | route | rule | neigh | tunnel | maddr | mroute | monitor }

ip link set DEVICE { up | down | arp { on | off } |

promisc { on | off } |
allmulti
{ on | off } |
dynamic
{ on | off } |
multicast
{ on | off } |
txqueuelen
PACKETS |
name
NEWNAME |
address
LLADDR | broadcast LLADDR |
mtu
MTU }

ip link [show] [ DEVICE ]

ip addr { add | del } IFADDR dev STRING

ip addr { show | flush } [ dev STRING ] [ scope SCOPE-ID ] [ to PREFIX ] [ FLAG-LIST ] [ label PATTERN ]

Where

IFADDR := PREFIX | ADDR peer PREFIX [ broadcast ADDR ] [ anycast ADDR ] [ label STRING ] [ scope SCOPE-ID ]

SCOPE-ID := [ host | link | global | NUMBER ]

FLAG-LIST := [ FLAG-LIST ] FLAG

FLAG := [ permanent | dynamic | secondary | primary | tentative | deprecated ]

ip route { list | flush } SELECTOR

ip route get ADDRESS [ from ADDRESS iif STRING ] [ oif STRING ] [ tos TOS ]

ip route { add | del | change | append | replace | monitor } ROUTE

SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ] [ table TABLE_ID ] [ proto RTPROTO ] [ type TYPE ] [ scope SCOPE ]

ROUTE := NODE_SPEC [ INFO_SPEC ]

NODE_SPEC := [ TYPE ] PREFIX [ tos TOS ] [ table TABLE_ID ] [ proto RTPROTO ] [ scope SCOPE ] [ metric METRIC ]

INFO_SPEC := NH OPTIONS FLAGS [ nexthop NH ] ...

NH := [ via ADDRESS ] [ dev STRING ] [ weight NUMBER ] NHFLAGS

OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ rtt NUMBER ] [ rttvar NUMBER ] [ window NUMBER ] [ cwnd NUMBER ] [ initcwnd NUMBER ] [ ssthresh REALM ] [ realms REALM ]

TYPE := [ unicast | local | broadcast | multicast | throw | unreachable | prohibit | blackhole | nat ]

TABLE_ID := [ local| main | default | all | NUMBER ]

SCOPE := [ host | link | global | NUMBER ]

FLAGS := [ equalize ]

NHFLAGS := [ onlink | pervasive ]

RTPROTO := [ kernel | boot | static | NUMBER ]

ip rule [ list | add | del | flush ] SELECTOR ACTION

SELECTOR := [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark FWMARK ] [ dev STRING ] [ pref NUMBER ]

ACTION := [ table TABLE_ID ] [ nat ADDRESS ] [ prohibit | reject | unreachable ] [ realms [SRCREALM/]DSTREALM ]

TABLE_ID := [ local | main | default | NUMBER ]

ip neigh { add | del | change | replace } { ADDR [ lladdr LLADDR ] [ nud { permanent | noarp | stale | reachable } ] | proxy ADDR } [ dev DEV ]

ip neigh { show | flush } [ to PREFIX ] [ dev DEV ] [ nud STATE ]

ip tunnel { add | change | del | show } [ NAME ]

[ mode { ipip | gre | sit } ]
[ remote ADDR ] [ local ADDR ]
[ [i|o]seq ] [ [i|o]key KEY ] [ [i|o]csum ] ]
[ ttl TTL ] [ tos TOS ] [ [no]pmtudisc ]
[ dev PHYS_DEV ]

Where

ip maddr [ add | del ] MULTIADDR dev STRING

ip maddr show [ dev STRING ]

ip mroute show [ PREFIX ] [ from PREFIX ] [ iif DEVICE ]

ip monitor [ all | LISTofOBJECTS ]

Options

-V, -Version

print the version of the ip utility and exit.
-s, -stats, -statistics
output more information. If the option appears twice or more, the amount of information increases. As a rule, the information is statistics or some time values.
-f, -family
followed by protocol family identifier: inet, inet6 or link ,enforce the protocol family to use. If the option is not present, the protocol family is guessed from other arguments. If the rest of the command line does not give enough information to guess the family, ip falls back to the default one, usually inet or any. link is a special family identifier meaning that no networking protocol is involved.
-4

shortcut for -family inet.

-6

shortcut for -family inet6.

-0

shortcut for -family link.

-o, -oneline
output each record on a single line, replacing line feeds with the '� character. This is convenient when you want to count records with wc(1) or to grep(1) the output.
-r, -resolve
use the system's name resolver to print DNS names instead of host addresses.

Ip - Command Syntax

OBJECT

link

- network device.

address
- protocol (IP or IPv6) address on a device.
neighbour
- ARP or NDISC cache entry.
route

- routing table entry.

rule

- rule in routing policy database.

maddress
- multicast address.
mroute

- multicast routing cache entry.

tunnel

- tunnel over IP.

The names of all objects may be written in full or abbreviated form, f.e. address is abbreviated as addr or just a.

COMMAND

Specifies the action to perform on the object. The set of possible actions depends on the object type. As a rule, it is possible to add, delete and show (or list ) objects, but some objects do not allow all of these operations or have some additional commands. The help command is available for all objects. It prints out a list of available commands and argument syntax conventions.

If no command is given, some default command is assumed. Usually it is list or, if the objects of this class cannot be listed, help.

ip link - network device configuration

link is a network device and the corresponding commands display and change the state of devices.

ip link set - change device attributes

dev NAME (default)
NAME specifies network device to operate on.
up and down
change the state of the device to UP or DOWN.
arp on or arp off
change the NOARP flag on the device.
multicast on or multicast off
change the MULTICAST flag on the device.
dynamic on or dynamic off
change the DYNAMIC flag on the device.
name NAME
change the name of the device. This operation is not recommended if the device is running or has some addresses already configured.
txqueuelen NUMBER
txqlen NUMBER
change the transmit queue length of the device.
mtu NUMBER
change the MTU of the device.
address LLADDRESS
change the station address of the interface.
broadcast LLADDRESS
brd LLADDRESS
peer LLADDRESS
change the link layer broadcast address or the peer address when the interface is POINTOPOINT.
Warning: If multiple parameter changes are requested, ip aborts immediately after any of the changes have failed. This is the only case when ip can move the system to an unpredictable state. The solution is to avoid changing several parameters with one ip link set call.

ip link show - display device attributes

dev NAME (default)
NAME specifies the network device to show. If this argument is omitted all devices are listed.
up

only display running interfaces.

ip address - protocol address management.

The address is a protocol (IP or IPv6) address attached to a network device. Each device must have at least one address to use the corresponding protocol. It is possible to have several different addresses attached to one device. These addresses are not discriminated, so that the term alias is not quite appropriate for them and we do not use it in this document.

The ip addr command displays addresses and their properties, adds new addresses and deletes old ones.

ip address add - add new protocol address.

dev NAME
the name of the device to add the address to.
local ADDRESS (default)
the address of the interface. The format of the address depends on the protocol. It is a dotted quad for IP and a sequence of hexadecimal halfwords separated by colons for IPv6. The ADDRESS may be followed by a slash and a decimal number which encodes the network prefix length.
peer ADDRESS
the address of the remote endpoint for pointopoint interfaces. Again, the ADDRESS may be followed by a slash and a decimal number, encoding the network prefix length. If a peer address is specified, the local address cannot have a prefix length. The network prefix is associated with the peer rather than with the local address.
broadcast ADDRESS
the broadcast address on the interface.

It is possible to use the special symbols '+' and '-' instead of the broadcast address. In this case, the broadcast address is derived by setting/resetting the host bits of the interface prefix.

label NAME
Each address may be tagged with a label string. In order to preserve compatibility with Linux-2.0 net aliases, this string must coincide with the name of the device or must be prefixed with the device name followed by colon.
scope SCOPE_VALUE
the scope of the area where this address is valid. The available scopes are listed in file /etc/iproute2/rt_scopes. Predefined scope values are:

global - the address is globally valid.

site - (IPv6 only) the address is site local, i.e. it is valid inside this site.

link - the address is link local, i.e. it is valid only on this device.

host - the address is valid only inside this host.

ip address delete - delete protocol address

Arguments: coincide with the arguments of ip addr add. The device name is a required argument. The rest are optional. If no arguments are given, the first address is deleted.

ip address show - look at protocol addresses

dev NAME (default)
name of device.
scope SCOPE_VAL
only list addresses with this scope.
to PREFIX
only list addresses matching this prefix.
label PATTERN
only list addresses with labels matching the PATTERN. PATTERN is a usual shell style pattern.
dynamic and permanent
(IPv6 only) only list addresses installed due to stateless address configuration or only list permanent (not dynamic) addresses.
tentative
(IPv6 only) only list addresses which did not pass duplicate address detection.
deprecated
(IPv6 only) only list deprecated addresses.
primary and secondary
only list primary (or secondary) addresses.

ip address flush - flush protocol addresses

This command flushes the protocol addresses selected by some criteria.

This command has the same arguments as show. The difference is that it does not run when no arguments are given.

Warning: This command (and other flush commands described below) is pretty dangerous. If you make a mistake, it will not forgive it, but will cruelly purge all the addresses.

With the -statistics option, the command becomes verbose. It prints out the number of deleted addresses and the number of rounds made to flush the address list. If this option is given twice, ip addr flush also dumps all the deleted addresses in the format described in the previous subsection.

ip neighbour - neighbour/arp tables management.

neighbour objects establish bindings between protocol addresses and link layer addresses for hosts sharing the same link. Neighbour entries are organized into tables. The IPv4 neighbour table is known by another name - the ARP table.

The corresponding commands display neighbour bindings and their properties, add new neighbour entries and delete old ones.

ip neighbour add - add a new neighbour entry

ip neighbour change - change an existing entry

ip neighbour replace - add a new entry or change an existing one

These commands create new neighbour records or update existing ones.
to ADDRESS (default)
the protocol address of the neighbour. It is either an IPv4 or IPv6 address.
dev NAME
the interface to which this neighbour is attached.
lladdr LLADDRESS
the link layer address of the neighbour. LLADDRESS can also be null.
nud NUD_STATE
the state of the neighbour entry. nud is an abbreviation for 'Neigh bour Unreachability Detection'. The state can take one of the following values:

permanent - the neighbour entry is valid forever and can be only be removed administratively.

noarp - the neighbour entry is valid. No attempts to validate this entry will be made but it can be removed when its lifetime expires.

reachable - the neighbour entry is valid until the reachability timeout expires.

stale - the neighbour entry is valid but suspicious. This option to ip neigh does not change the neighbour state if it was valid and the address is not changed by this command.

ip neighbour delete - delete a neighbour entry

This command invalidates a neighbour entry.

The arguments are the same as with ip neigh add, except that lladdr and nud are ignored.

Warning: Attempts to delete or manually change a noarp entry created by the kernel may result in unpredictable behaviour. Particularly, the kernel may try to resolve this address even on a NOARP interface or if the address is multicast or broadcast.

ip neighbour show - list neighbour entries

This commands displays neighbour tables.
to ADDRESS (default)
the prefix selecting the neighbours to list.
dev NAME
only list the neighbours attached to this device.
unused

only list neighbours which are not currently in use.

nud NUD_STATE
only list neighbour entries in this state. NUD_STATE takes values listed below or the special value all which means all states. This option may occur more than once. If this option is absent, ip lists all entries except for none and noarp.

ip neighbour flush - flush neighbour entries

This command flushes neighbour tables, selecting entries to flush by some criteria.

This command has the same arguments as show. The differences are that it does not run when no arguments are given, and that the default neighbour states to be flushed do not include permanent and noarp.

With the -statistics option, the command becomes verbose. It prints out the number of deleted neighbours and the number of rounds made to flush the neighbour table. If the option is given twice, ip neigh flush also dumps all the deleted neighbours.

ip route - routing table management

Manipulate route entries in the kernel routing tables keep information about paths to other networked nodes.

Route types:

unicast - the route entry describes real paths to the destinations covered by the route prefix.

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

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

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

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

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

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 net unreachable is generated. The local senders get an ENETUNREACH error.

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 Warning: Route NAT is no longer supported in Linux 2.6.

via.

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

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

Route tables

Linux can pack routes into several routing tables identified by a number in the range from 1 to 255 or by name from the file /etc/iproute2/rt_tables main table (ID 254) and the kernel only uses this table when calculating routes.

Actually, one other table always exists, which is invisible but even more important. It is the 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 policy routing is used.

ip route add - add new route

ip route change - change route

ip route replace - change or add new one

to TYPE PREFIX (default)
the destination prefix of the route. If TYPE is omitted, ip assumes type unicast. Other values of TYPE are listed above. PREFIX is an IP or IPv6 address optionally followed by a slash and the prefix length. If the length of the prefix is missing, ip assumes a full-length host route. There is also a special PREFIX default - which is equivalent to IP 0/0 or to IPv6 ::/0.
tos TOS
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. TOS is either an 8 bit hexadecimal number or an identifier from /etc/iproute2/rt_dsfield.
metric NUMBER
preference NUMBER
the preference value of the route. NUMBER is an arbitrary 32bit number.
table TABLEID
the table to add this route to. TABLEID may be a number or a string from the file /etc/iproute2/rt_tables. If this parameter is omitted, ip assumes the main table, with the exception of local , broadcast and nat routes, which are put into the local table by default.
dev NAME
the output device name.
via ADDRESS
the address of the nexthop router. Actually, the sense of this field depends on the route type. For normal 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.
src ADDRESS
the source address to prefer when sending to the destinations covered by the route prefix.
realm REALMID
the realm to which this route is assigned. REALMID may be a number or a string from the file /etc/iproute2/rt_realms.
mtu MTU
mtu lock MTU
the MTU along the path to the destination. If the modifier lock is not used, the MTU may be updated by the kernel due to Path MTU Discovery. If the modifier 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.
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.
rtt NUMBER
the initial RTT ('Round Trip Time') estimate.
rttvar NUMBER (2.3.15+ only)
the initial RTT variance estimate.
ssthresh NUMBER (2.3.15+ only)
an estimate for the initial slow start threshold.
cwnd NUMBER (2.3.15+ only)
the clamp for congestion window. It is ignored if the lock flag is not used.
initcwnd NUMBER
The maximum initial congestion window (cwnd) size in MSS of a TCP connection.
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.)
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 sysctl variable net/ipv4/tcp_reordering.
nexthop NEXTHOP
the nexthop of a multipath route. NEXTHOP is a complex value with its own syntax similar to the top level argument lists:

via ADDRESS - is the nexthop router.

dev NAME - is the output device.

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

scope SCOPE_VAL
the scope of the destinations covered by the route prefix. SCOPE_VAL may be a number or a string from the file /etc/iproute2/rt_scopes. If this parameter is omitted, ip assumes scope global for all gatewayed unicast routes, scope link for direct unicast and broadcast routes and scope host for local routes.
protocol RTPROTO
the routing protocol identifier of this route. RTPROTO may be a number or a string from the file /etc/iproute2/rt_protos. If the routing protocol ID is not given, ip assumes protocol 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:

redirect - the route was installed due to an ICMP redirect.

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

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

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.

ra - the route was installed by Router Discovery protocol.

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

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

equalize
allow packet by packet randomization on multipath routes. Without this modifier, the route will be frozen to one selected nexthop, so that load splitting will only occur on per-flow base. equalize only works if the kernel is patched.

ip route delete - delete route

ip route del has the same arguments as ip route add, but their semantics are a bit different.

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

ip route show - list routes

the command displays the contents of the routing tables or the route(s) selected by some criteria.
to SELECTOR (default)
only select routes from the given range of destinations. SELECTOR consists of an optional modifier (root, match or exact) and a prefix. root PREFIX selects routes with prefixes not shorter than PREFIX. F.e. root 0/0 selects the entire routing table. match PREFIX selects routes with prefixes not longer than PREFIX. F.e. match 10.0/16 selects 10.0/16, 10/8 and 0/0, but it does not select 10.1/16 and 10.0.0/24. And exact PREFIX (or just PREFIX) selects routes with this exact prefix. If neither of these options are present, ip assumes root 0/0 i.e. it lists the entire table.
tos TOS
dsfield TOS only select routes with the given TOS.
table TABLEID
show the routes from this table(s). The default setting is to show tablemain. TABLEID may either be the ID of a real table or one of the special values:

all - list all of the tables.

cache - dump the routing cache.

cloned

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 table cache.

from SELECTOR
the same syntax as for to, but it binds the source address range rather than destinations. Note that the from option only works with cloned routes.
protocol RTPROTO
only list routes of this protocol.
scope SCOPE_VAL
only list routes with this scope.
type TYPE
only list routes of this type.
dev NAME
only list routes going via this device.
via PREFIX
only list routes going via the nexthop routers selected by PREFIX.
src PREFIX
only list routes with preferred source addresses selected by PREFIX.
realm REALMID
realms FROMREALM/TOREALM
only list routes with these realms.

ip route flush - flush routing tables

this command flushes routes selected by some criteria.

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

With the -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, ip route flush also dumps all the deleted routes in the format described in the previous subsection.

ip route get - get a single route

this command gets a single route to a destination and prints its contents exactly as the kernel sees it.
to ADDRESS (default)
the destination address.
from ADDRESS
the source address.
tos TOS
dsfield TOS
the Type Of Service.
iif NAME
the device from which this packet is expected to arrive.
oif NAME
force the output device on which this packet will be routed.
connected
if no source address (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.
Note that this operation is not equivalent to ip route show. show shows existing routes. get resolves them and creates new clones if necessary. Essentially, get is equivalent to sending a packet along this path. If the 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 ip route ls cache, however, no packets are actually sent. With the iif argument, the kernel pretends that a packet arrived from this interface and searches for a path to forward the packet.

ip rule - routing policy database management

Rules in the routing policy database control the route selection algorithm.

Classic routing algorithms used in the Internet make routing decisions based only on the destination address of packets (and in theory, but not in practice, on the TOS field).

In some circumstances we want to route packets differently depending not only on destination addresses, but also on other packet fields: source address, IP protocol, transport protocol ports or even packet payload. This task is called 'policy routing'.

To solve this task, the conventional destination based routing table, ordered according to the longest match rule, is replaced with a 'routing policy database' (or RPDB), which selects routes by executing some set of rules.

Each policy routing rule consists of a selector and an action predicate. The RPDB is scanned in the order of increasing priority. The selector of each rule is applied to {source address, destination address, incoming interface, tos, fwmark} and, if the selector matches the packet, the action is performed. The action predicate may return with success. In this case, it will either give a route or failure indication and the RPDB lookup is terminated. Otherwise, the RPDB program continues on the next rule.

Semantically, natural action is to select the nexthop and the output device.

At startup time the kernel configures the default RPDB consisting of three rules:

1.

Priority: 0, Selector: match anything, Action: lookup routing table local (ID 255). The local table is a special routing table containing high priority control routes for local and broadcast addresses.

Rule 0 is special. It cannot be deleted or overridden.
2.

Priority: 32766, Selector: match anything, Action: lookup routing table main (ID 254). The main table is the normal routing table containing all non-policy routes. This rule may be deleted and/or overridden with other ones by the administrator.

3.

Priority: 32767, Selector: match anything, Action: lookup routing table default (ID 253). The default table is empty. It is reserved for some post-processing if no previous default rules selected the packet. This rule may also be deleted.

Each RPDB entry has additional attributes. F.e. each rule has a pointer to some routing table. NAT and masquerading rules have an attribute to select new IP address to translate/masquerade. Besides that, rules have some optional attributes, which routes have, namely realms. These values do not override those contained in the routing tables. They are only used if the route did not select any attributes.

The RPDB may contain rules of the following types:

unicast - the rule prescribes to return the route found in the routing table referenced by the rule.

blackhole - the rule prescribes to silently drop the packet.

unreachable - the rule prescribes to generate a 'Network is unreachable' error.

prohibit - the rule prescribes to generate 'Communication is administratively prohibited' error.

nat - the rule prescribes to translate the source address of the IP packet into some other value.

ip rule add - insert a new rule

ip rule delete - delete a rule

type TYPE (default)
the type of this rule. The list of valid types was given in the previous subsection.
from PREFIX
select the source prefix to match.
to PREFIX
select the destination prefix to match.
iif NAME
select the incoming device to match. If the interface is loopback, the rule only matches packets originating from this host. This means that you may create separate routing tables for forwarded and local packets and, hence, completely segregate them.
tos TOS
dsfield TOS
select the TOS value to match.
fwmark MARK
select the fwmark value to match.
priority PREFERENCE
the priority of this rule. Each rule should have an explicitly set unique priority value.
table TABLEID
the routing table identifier to lookup if the rule selector matches.
realms FROM/TO
Realms to select if the rule matched and the routing table lookup succeeded. Realm TO is only used if the route did not select any realm.
nat ADDRESS
The base of the IP address block to translate (for source addresses). The ADDRESS may be either the start of the block of NAT addresses (selected by NAT routes) or a local host address (or even zero). In the last case the router does not translate the packets, but masquerades them to this address.

Warning: Changes to the RPDB made with these commands do not become active immediately. It is assumed that after a script finishes a batch of updates, it flushes the routing cache with ip route flush cache.

ip rule flush - also dumps all the deleted rules.

This command has no arguments.

ip rule show - list rules

This command has no arguments.

ip maddress - multicast addresses management

maddress objects are multicast addresses.

ip maddress show - list multicast addresses

dev NAME (default)
the device name.

ip maddress add - add a multicast address

ip maddress delete - delete a multicast address

these commands attach/detach a static link layer multicast address to listen on the interface. Note that it is impossible to join protocol multicast groups statically. This command only manages link layer addresses.
address LLADDRESS (default)
the link layer multicast address.
dev NAME
the device to join/leave this multicast address.

ip mroute - multicast routing cache management

mroute objects are multicast routing cache entries created by a user level mrouting daemon (f.e. pimd or mrouted ).

Due to the limitations of the current interface to the multicast routing engine, it is impossible to change mroute objects administratively, so we may only display them. This limitation will be removed in the future.

ip mroute show - list mroute cache entries

to PREFIX (default)
the prefix selecting the destination multicast addresses to list.
iif NAME
the interface on which multicast packets are received.
from PREFIX
the prefix selecting the IP source addresses of the multicast route.

ip tunnel - tunnel configuration

tunnel objects are tunnels, encapsulating packets in IPv4 packets and then sending them over the IP infrastructure.

ip tunnel add - add a new tunnel

ip tunnel change - change an existing tunnel

ip tunnel delete - destroy a tunnel

name NAME (default)
select the tunnel device name.
mode MODE
set the tunnel mode. Three modes are currently available: ipip, sit and gre.
remote ADDRESS
set the remote endpoint of the tunnel.
local ADDRESS
set the fixed local address for tunneled packets. It must be an address on another interface of this host.
ttl N

set a fixed TTL N on tunneled packets. N is a number in the range 1--255. 0 is a special value meaning that packets inherit the TTL value. The default value is: inherit.

tos T

dsfield T
set a fixed TOS T on tunneled packets. The default value is: inherit.
dev NAME
bind the tunnel to the device NAME so that tunneled packets will only be routed via this device and will not be able to escape to another device when the route to endpoint changes.
nopmtudisc
disable Path MTU Discovery on this tunnel. It is enabled by default. Note that a fixed ttl is incompatible with this option: tunnelling with a fixed ttl always makes pmtu discovery.
key K

ikey K

okey K

( only GRE tunnels ) use keyed GRE with key K. K is either a number or an IP address-like dotted quad. The key parameter sets the key to use in both directions. The ikey and okey parameters set different keys for input and output.

csum, icsum, ocsum
( only GRE tunnels ) generate/require checksums for tunneled packets. The ocsum flag calculates checksums for outgoing packets. The icsum flag requires that all input packets have the correct checksum. The csum flag is equivalent to the combination icsum ocsum.
seq, iseq, oseq
( only GRE tunnels ) serialize packets. The oseq flag enables sequencing of outgoing packets. The iseq flag requires that all input packets are serialized. The seq flag is equivalent to the combination iseq oseq. It isn't work. Don't use it.

ip tunnel show - list tunnels

This command has no arguments.

ip monitor and rtmon - state monitoring

The ip utility can monitor the state of devices, addresses and routes continuously. This option has a slightly different format. Namely, the monitor command is the first in the command line and then the object list follows:

ip monitor [ all | LISTofOBJECTS ]

OBJECT-LIST is the list of object types that we want to monitor. It may contain link, address and route. If no file argument is given, ip opens RTNETLINK, listens on it and dumps state changes in the format described in previous sections.

If a file name is given, it does not listen on RTNETLINK, but opens the file containing RTNETLINK messages saved in binary format and dumps them. Such a history file can be generated with the rtmon utility. This utility has a command line syntax similar to ip monitor. Ideally, rtmon should be started before the first network configuration command is issued. F.e. if you insert:

rtmon file /var/log/rtmon.log
in a startup script, you will be able to view the full history later.

Certainly, it is possible to start rtmon at any time. It prepends the history with the state snapshot dumped at the moment of starting.

History

ip was written by Alexey N. Kuznetsov and added in Linux 2.2.

See Also

tc(8)
IP Command reference ip-cref.ps
IP tunnels ip-cref.ps

Author

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

Referenced By

avahi-autoipd.action(8), ifrename(8), iftab(5), ipsec_pluto(8), linkloop(1), lnstat(8), miredo(8), netplugd(8), rtmon(8), ss(8), tc-pfifo(8), tc-pfifo_fast(8), vconfig(8), vpnc(8)
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12 ip Command Examples for Linux Users

12 ip Command Examples for Linux Users

For years & years we have been using 'ifconfig' command to perform network related tasks like checking network interfaces or configuring them. But 'ifconfig' is no longer being maintained & has been deprecated on the recent versions of Linux. 'ifconfig' command has been replaced with 'ip' command.

'ip' command is somewhat similar to 'ifconfig' command but it's much more powerful with much more functionalities attached to it. 'ip' command is able to perform several tasks which were not possible to perform with 'ifconfig' command.

IP-command-examples-Linux

In this tutorial, we are going to discuss 12 most common uses for 'ip' command, so let's get going,

Example 1: Checking network information for interfaces ( LAN Cards )

To check the network information like IP address, Subnet etc for the interfaces, use 'ip addr show' command

[linuxtechi@localhost]$ ip addr show

or

[linuxtechi@localhost]$ ip a s

This will show network information related to all interfaces available on our system, but if we want to view same information for single interface, command is

[linuxtechi@localhost]$ ip addr show enp0s3

where enp0s3 is the name of the interface.

IP-addr-show-commant-output

Example 2: Enabling & disabling a network interface

To enable a disable network interface, 'ip' command used is

[linuxtechi@localhost]$ sudo ip link set enp0s3 up

& to disable the network interface we will use 'down' trigger,

[linuxtechi@localhost]$ sudo ip link set enp0s3 down

Example 3: Assigning IP address & other network information to an interface

To assign IP address to interface, we will use

[linuxtechi@localhost]$ sudo ip addr add 192.168.0.50/255.255.255.0 dev enp0s3

We can also set broadcast address to interface with 'ip' command. By default no broadcast address is set, so to set a broadcast address command is

[linuxtechi@localhost]$ sudo  ip addr add broadcast 192.168.0.255 dev enp0s3

We can also set standard broadcast address along with IP address by using the following command,

[linuxtechi@localhost]$  sudo ip addr add 192.168.0.10/24 brd + dev enp0s3

As shown in the above example, we can also use 'brd' in place on 'broadcast' to set broadcast ip address.

Example 4: Removing IP address from interface

If we want to flush or remove the assigned IP from interface, then the beneath ip command

[linuxtechi@localhost]$ sudo ip addr del 192.168.0.10/24 dev enp0s3

Example 5: Adding an Alias for an interface (enp0s3)

To add an alias i.e. assign more than one IP to an interface, execute below command

[linuxtechi@localhost]$  sudo ip addr add 192.168.0.20/24 dev enp0s3 label enp0s3:1

ip-command-add-alias-linux

Example 6: Checking route or default gateway information

Checking routing information shows us the route a packet will take to reach the destination. To check the network routing information, execute the following command,

[linuxtechi@localhost]$  ip route show

ip-route-command-output

In the output we will see the routing information for packets for all the network interfaces. We can also get the routing information to a particular ip using,

[linuxtechi@localhost]$ sudo ip route get 192.168.0.1

Example 7: Adding a static route

If we want to change the default route taken by packets, we can do so with IP command. To assign a default gateway, use following 'ip route' command

[linuxtechi@localhost]$ sudo ip route add default via 192.168.0.150/24

So now all network packets will travel via 192.168.0.150 as opposed to old default route. For changing the default route for a single interface & to make change route further, execute

[linuxtechi@localhost]$ sudo ip route add 172.16.32.32 via 192.168.0.150/24 dev enp0s3

Example 8: Removing a static route

To remove the a previously changes default route, open terminal & run,

[linuxtechi@localhost]$  sudo ip route del 192.168.0.150/24

Note:- Changes made to default route using the above mentioned commands are only temporary & all changes will be lost after a system has been restarted. To make a persistence route change, we need to modify / create route-enp0s3 file . Add the following line to it, demonstration is shown below

[linuxtechi@localhost]$  sudo vi /etc/sysconfig/network-scripts/route-enp0s3

172.16.32.32 via 192.168.0.150/24 dev enp0s3

Save and Exit the file.

If you are using Ubuntu or debian based OS, than the location of the file is '/etc/network/interfaces' and add the line "ip route add 172.16.32.32 via 192.168.0.150/24 dev enp0s3" to the bottom of the file.

Example 9: Checking all ARP entries

ARP, short for 'Address Resolution Protocol' , is used to convert an IP address to physical address (also known as MAC address) & all the IP and their corresponding MAC details are stored in a table known as ARP cache.

To view entries in ARP cache i.e. MAC addresses of the devices connected in LAN, the IP command used is

[linuxtechi@localhost]$  ip neigh

ip-neigh-command-linux

Example 10: Modifying ARP entries

To delete an ARP entry, the command used is

[linuxtechi@localhost]$ sudo ip neigh del 192.168.0.106 dev enp0s3

or if we want to add a new entry to ARP cache, the command is

[linuxtechi@localhost]$ sudo ip neigh add 192.168.0.150 lladdr 33:1g:75:37:r3:84 dev enp0s3 nud perm

where nud means neighbour state, it can be

  • perm – permanent & can only be removed by administrator,
  • noarp – entry is valid but can be removed after lifetime expires,
  • stale – entry is valid but suspicious,
  • reachable – entry is valid until timeout expires.

Example 11: Checking network statistics

With 'ip' command we can also view the network statistics like bytes and packets transferred, errors or dropped packets etc for all the network interfaces. To view network statistics, use 'ip -s link' command

[linuxtechi@localhost]$ ip -s link

ip-s-command-linux

Example 12: How to get help

If you want to find a option which is not listed in above examples, then you can look for help. In Fact you can use help for all the commands. To list all available options that can be used with 'ip' command, use

[linuxtechi@localhost]$ ip help

Remember that 'ip' command is very important command for Linux admins and it should be learned and mastered to configure network with ease. That's it for now, please do provide your suggestions & leave your queries in the comment box below.

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