Linux ip command

On Linux operating systems, the ip command edits and displays the configuration of network interfaces, routing, and tunnels. On many Linux systems, it replaces the deprecated ifconfig command.

Syntax

ip [ OPTIONS ] OBJECT { COMMAND | help }

where OBJECT may be:

{ link | addr | addrlabel | route | rule | neigh | ntable | tunnel |
tuntap maddr | mroute | mrule | monitor | xfrm | netns | l2tp | tcp_metrics }

and OPTIONS may be:

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

Options

Object

The names of all objects may be written in full or abbreviated form (e.g., 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 changes device attributes:

ip link set DEVICE { up | down | arp { on | off } |
            promisc { on | off } |
            allmulticast { on | off } |
            dynamic { on | off } |
            multicast { on | off } |
            txqueuelen PACKETS |
            name NEWNAME |
            address LLADDR | broadcast LLADDR |
            mtu MTU |
            netns PID |
            alias NAME |
            vf NUM [ mac LLADDR ]
            [ vlan VLANID [ qos VLAN-QOS ] ]
            [ rate TXRATE ] } 

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 displays device attributes:

ip link show [ DEVICE ]

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 different addresses attached to one device. These addresses are not discriminated, so the term alias is not quite appropriate for them and we do not use it in this page.

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

ip address add adds a new protocol address:

ip address add IFADDR dev NAME

ip address delete deletes a protocol address:

The arguments for ip address delete are the same as the arguments of ip addr add (see above). The device name is a required argument; the rest are optional. If no arguments are given, the first address is deleted.

ip address show looks at protocol addresses:

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

ip address flush flushes a protocol addresses:

This command flushes the protocol addresses selected by some criteria.

This command has the same arguments as show (see above). 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 addrlabel: Protocol Address Label Management

IPv6 address label is used for address selection described in RFC 3484. Precedence is managed by userspace, and only label is stored in kernel.

ip addrlabel add adds an address label entry to the kernel:

ip addrlabel { add | del } prefix PREFIX [ dev DEV ] [ label NUMBER ]

ip addrlabel { list | flush }

ip addrlabel del flushes address labels:

the command deletes an address label entry in the kernel. Arguments coincide with the arguments of ip addrlabel add but label is not required.

ip addrlabel list lists address labels:

this command shows contents of address labels.

ip addrlabel flush flushes address labels:

this command flushes the contents of address labels and does not restore default settings.

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

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

ip neighbour delete deletes a neighbour entry:

This command invalidates a neighbour entry.

The arguments are the same as with ip neighbor 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 neighbor { show | flush } [ to PREFIX ] [ dev DEV ] [ nud STATE ]

ip neighbour show lists neighbour entries:

This command displays neighbour tables.

ip neighbour flush flushes 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 neighbor flush also dumps all the deleted neighbours.

ip route manages routing tables:

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

Route types:

Route tables:

Linux-2.x 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 By default, all normal routes are inserted into the 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 get involved when policy routing is used.

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

ip route add - add new route

ip route change - change route

ip route replace - change route, or add new route

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

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.

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.

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.

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

ip rule add - insert a new rule

ip rule delete - delete a rule

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. The options list or lst are synonyms with show.

ip maddress - multicast addresses management

maddress objects are multicast addresses.

ip maddress show [ dev STRING ]

ip maddress [ add | del ] MULTIADDR dev STRING

ip maddress show - list multicast addresses

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.

ip mroute - multicast routing cache management

mroute objects are multicast routing cache entries created by a user level mrouting daemon (e.g., 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. According to the authors, this limitation will be removed in the future.

ip mroute show - list mroute cache entries

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

ip tunnel - tunnel configuration

tunnel objects are tunnels, encapsulating packets in IP packets and then sending them over the IP infrastructure. The encapulating (or outer) address family is specified by the -f option. The default is IPv4.

ip tunnel { add | change | del | show | prl } [ NAME ] [ mode MODE ]
          [ remote ADDR ] [ local ADDR ] [ [i|o]seq ] [ [i|o]key KEY ]
          [ [i|o]csum ] ] [ encaplimit ELIM ] [ ttl TTL ] [ tos TOS ]
          [ flowlabel FLOWLABEL ] [ prl-default ADDR ] [ prl-nodefault ADDR ]
          [ prl-delete ADDR ] [ [no]pmtudisc ] [ dev PHYS_DEV ] [ dscp inherit ]

ip tunnel add - add a new tunnel

ip tunnel change - change an existing tunnel

ip tunnel delete - destroy a tunnel

ip tunnel prl - potential router list (ISATAP only)

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 | OBJECT-LIST ]

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. For example, 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.

ip xfrm - setting xfrm

xfrm is an IP framework, which can transform format of the datagrams, i.e., encrypt the packets with some algorithm. xfrm policy and xfrm state are associated through templates TMPL_LIST. This framework is used as a part of IPsec protocol.

ip xfrm state { add | update } ID [ XFRM_OPT ] [ mode MODE ] [ reqid REQID ]
              [ seq SEQ ] [ replay-window SIZE ] [ flag FLAG-LIST ]
              [ encap ENCAP ] [ sel SELECTOR ] [ LIMIT-LIST ]

ip xfrm state allocspi ID [ mode MODE ] [ reqid REQID ] [ seq SEQ ]
              [ min SPI max SPI ]

ip xfrm state add - add new state into xfrm

ip xfrm state update - update existing xfrm state

ip xfrm state allocspi - allocate SPI (Stateful Packet Inspection) value

ip xfrm policy { add | update } dir DIR SELECTOR [ index INDEX ]
               [ ptype PTYPE ] [ action ACTION ] [ priority PRIORITY ]
               [ LIMIT-LIST ] [ TMPL-LIST ]

ip xfrm policy { delete | get } dir DIR [ SELECTOR | index INDEX ]
               [ ptype PTYPE ]

ip xfrm policy { deleteall | list } [ dir DIR ] [ SELECTOR ]
               [ index INDEX ] [ action ACTION ] [ priority PRIORITY ]

ip xfrm policy flush [ ptype PTYPE ]

ip xfrm policy add - add a new policy

ip xfrm policy update - update an existing policy

ip xfrm policy delete - delete existing policy

ip xfrm policy get - get existing policy

ip xfrm policy deleteall - delete all existing xfrm policy

ip xfrm policy list - print out the list of xfrm policy

ip xfrm policy flush - flush policies

ip xfrm policy flush can flush all policies or only those specified with ptype.

ip xfrm monitor [ all | OBJECT-LIST ]

ip xfrm monitor - is used for listing all objects or defined group of them.

xfrm monitor can monitor the policies for all objects or defined group of them.

Examples

ip addr show

Lists the network interfaces.

ip route show

Lists the routing table.

ip addr add 104.20.56.118 dev eth1

Assign the IP address 104.20.56.118 to Ethernet device eth1.

A note about other operating systems

If you are using another Unix-like operating system such as BSD or macOS X (whose foundations are based upon BSD), the ip command may not be available; however the same, or very closely similar, functionality can be achieved using the route command. For instance, this Linux ip command:

ip route get 74.125.226.35

...which outputs:

74.125.226.35 via 192.168.1.1 dev wlan0  src 192.168.1.2
cache

...is similar to this OS X route command:

route get 74.125.226.35

route to: lga15s43-in-f3.1e100.net
destination: default
       mask: default
    gateway: 192.168.1.1
  interface: en1
      flags: <UP,GATEWAY,DONE,STATIC,PRCLONING>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0         0         0         0      1500         0

Note that this form of the route command is BSD-specific, and does not carry over to Linux route. Also, note that the route command performs DNS resolution, but ip does not. Therefore, on BSD, this command will work:

route get google.com

...but this Linux command:

ip route get google.com

...will not, because it needs an IP address, and cannot (by design) resolve the domain name on its own.

There are many differences between these types of kernel-level utilities on varying operating systems despite the fact they often share the same command name, and it's advisable to check your operating system's manual pages for exact usage details.

Related commands

arp — Manipulate the system ARP cache.
ifconfig — View or modify the configuration of network interfaces.
netstat — Print information about network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
route — Display and manipulate the IP routing table.
tcpdump — Capture raw network traffic.