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Exploring the Linux ‘ip’ Command

I’ve been speaking for a number of years now about how community engineers must turn out to be snug with Linux. I usually place it that we don’t all must turn out to be “massive bushy beard-bearing sysadmins.” Reasonably, community engineers should be capable to navigate and work with a Linux-based system confidently. I’m not going to enter all the explanations I imagine that on this put up (for those who’d like a deeper exploration of that matter, please let me know). Nope… I need to dive into a selected ability that each community engineer ought to have: exploring the community configuration of a Linux system with the “ip” command.

A winding introduction with some psychology and an embarrassing reality (or two)

If you’re like me and began your computing world on a Home windows machine, perhaps you’re aware of “ipconfig” on Home windows. The “ipconfig” command offers particulars concerning the community configuration from the command line.

A very long time in the past, earlier than Hank centered on community engineering and earned his CCNA for the primary time, he used the “ipconfig” command fairly recurrently whereas supporting Home windows desktop methods.

What was the IP assigned to the system? Was DHCP working accurately? What DNS servers are configured? What’s the default gateway? What number of interfaces are configured on the system? So many questions he’d use this command to reply. (He additionally sometimes began speaking within the third particular person.)

It was an incredible a part of my toolkit. I’m really smiling in nostalgia as I kind this paragraph. 🙂

For outdated instances’ sake, I requested John Capobianco, one in all my latest co-workers right here at Cisco Studying & Certifications, to ship me the output from “ipconfig /all” for the weblog. John is a diehard Home windows consumer nonetheless, whereas I transformed to Mac a few years in the past. And right here is the output of one in all my favourite Home windows instructions (edited for some privateness information).

Home windows IP Configuration

   Host Title . . . . . . . . . . . . : WINROCKS
   Major Dns Suffix  . . . . . . . :
   Node Sort . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search Record. . . . . . :

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : house
   Description . . . . . . . . . . . : Intel(R) Ethernet Connection (12) I219-V
   Bodily Handle. . . . . . . . . : 24-4Q-FE-88-HH-XY
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure
   Hyperlink-local IPv6 Handle . . . . . : fe80::31fa:60u2:bc09:qq45percent13(Most well-liked)
   IPv4 Handle. . . . . . . . . . . : well-liked)
   Subnet Masks . . . . . . . . . . . :
   Lease Obtained. . . . . . . . . . : July 22, 2022 8:30:42 AM
   Lease Expires . . . . . . . . . . : July 25, 2022 8:30:41 AM
   Default Gateway . . . . . . . . . :
   DHCP Server . . . . . . . . . . . :
   DHCPv6 IAID . . . . . . . . . . . : 203705342
   DHCPv6 Consumer DUID. . . . . . . . : 00-01-00-01-27-7B-B2-1D-24-4Q-FE-88-HH-XY
   DNS Servers . . . . . . . . . . . :
   NetBIOS over Tcpip. . . . . . . . : Enabled

Wi-fi LAN adapter Wi-Fi:

   Media State . . . . . . . . . . . : Media disconnected
   Connection-specific DNS Suffix  . : house
   Description . . . . . . . . . . . : Intel(R) Wi-Fi 6 AX200 160MHz
   Bodily Handle. . . . . . . . . : C8-E2-65-8U-ER-BZ
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure

Ethernet adapter Bluetooth Community Connection:

   Media State . . . . . . . . . . . : Media disconnected
   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Bluetooth Machine (Private Space Community)
   Bodily Handle. . . . . . . . . : C8-E2-65-A7-ER-Z8
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure

It’s nonetheless such an incredible and useful command. Just a few new issues in there from once I was utilizing it each day (IPv6, WiFi, Bluetooth), however it nonetheless appears like I bear in mind.

The primary time I needed to contact and work on a Linux machine, I felt like I used to be on a brand new planet. Every part was totally different, and it was ALL command line. I’m not ashamed to confess that I used to be slightly intimidated. However then I discovered the command “ifconfig,” and I started to breathe slightly simpler. The output didn’t look the identical, however the command itself was shut. The data it confirmed was straightforward sufficient to learn. So, I gained a little bit of confidence and knew, “I can do that.”

Once I jumped onto the DevNet Skilled CWS VM that I’m utilizing for this weblog to seize the output of the “ifconfig” command for example, I used to be offered with this output.

(essential) skilled@expert-cws:~$ ifconfig

Command 'ifconfig' not discovered, however will be put in with:

apt set up net-tools
Please ask your administrator.

This brings me to the purpose of this weblog put up. The “ifconfig” command is now not the very best command for viewing the community interface configuration in Linux. In reality, it hasn’t been the “finest command” for a very long time. Immediately the “ip” command is what we must be utilizing.  I’ve identified this for some time, however giving up one thing that made you are feeling snug and protected is difficult. Simply ask my 13-year-old son, who nonetheless sleeps with “Brown Canine,” the small stuffed pet I gave him the day he was born. As for me, I resisted studying and transferring to the “ip” command for much longer than I ought to have.

Finally, I noticed that I wanted to get with the instances. I began utilizing the “ip” command on Linux. You understand what, it’s a very nice command. The “ip” command is way extra highly effective than “ifconfig.”

When I discovered myself fascinated about a subject for a weblog put up, I figured there is perhaps one other engineer or two on the market who may admire a private introduction to the “ip” command from Hank.

However earlier than we dive in, I can’t depart a cliffhanger like that on the “ifconfig” command.

root@expert-cws:~# apt-get set up net-tools

(essential) skilled@expert-cws:~$ ifconfig
docker0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        ether 02:42:9a:0c:8a:ee  txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  body 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  provider 0  collisions 0

ens160: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        inet6 fe80::20c:29ff:fe75:9927  prefixlen 64  scopeid 0x20
        ether 00:0c:29:75:99:27  txqueuelen 1000  (Ethernet)
        RX packets 85468  bytes 123667981 (123.6 MB)
        RX errors 0  dropped 0  overruns 0  body 0
        TX packets 27819  bytes 3082651 (3.0 MB)
        TX errors 0  dropped 0 overruns 0  provider 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet  netmask
        inet6 ::1  prefixlen 128  scopeid 0x10
        loop  txqueuelen 1000  (Native Loopback)
        RX packets 4440  bytes 2104825 (2.1 MB)
        RX errors 0  dropped 0  overruns 0  body 0
        TX packets 4440  bytes 2104825 (2.1 MB)
        TX errors 0  dropped 0 overruns 0  provider 0  collisions 0

There it’s, the command that made me really feel slightly higher once I began working with Linux.

Exploring the IP configuration of your Linux host with the “ip” command!

So there you’re, a community engineer sitting on the console of a Linux workstation, and you have to discover or change the community configuration. Let’s stroll by means of a little bit of “networking 101” with the “ip” command.

First up, let’s see what occurs after we simply run “ip.”

(essential) skilled@expert-cws:~$ ip
Utilization: ip [ OPTIONS ] OBJECT  assist 
       ip [ -force ] -batch filename
the place  OBJECT :=  mrule 
       OPTIONS := { -V[ersion] | -s[tatistics] | -d[etails] | -r[esolve] |
                    -h[uman-readable] | -iec | -j[son] | -p[retty] |
                    -f[amily]  mpls  |
                    -4 | -6 | -I | -D | -M | -B | -0 |
                    -l[oops] { maximum-addr-flush-attempts } | -br[ief] |
                    -o[neline] | -t[imestamp] | -ts[hort] | -b[atch] [filename] |
                    -rc[vbuf] [size] | -n[etns] title | -N[umeric] | -a[ll] |

There’s some attention-grabbing information simply on this assist/utilization message. It appears like “ip” requires an OBJECT on which a COMMAND is executed. And the doable objects embrace a number of that leap out on the community engineer within me.

  • hyperlink – I’m curious what “hyperlink” means on this context, however it catches my eye for certain
  • deal with – That is actually promising. The ip “addresses” assigned to a bunch is excessive on the checklist of issues I do know I’ll need to perceive.
  • route – I wasn’t totally anticipating “route” to be listed right here if I’m pondering when it comes to the “ipconfig” or “ifconfig” command. However the routes configured on a bunch is one thing I’ll be inquisitive about.
  • neigh – Neighbors? What sort of neighbors?
  • tunnel – Oooo… tunnel interfaces are undoubtedly attention-grabbing to see right here.
  • maddress, mroute, mrule – My preliminary thought once I noticed “maddress” was “MAC deal with,” however then I appeared on the subsequent two objects and thought perhaps it’s “multicast deal with.” We’ll depart “multicast” for an additional weblog put up. 🙂

The opposite objects within the checklist are attention-grabbing to see. Having “netconf” within the checklist was a cheerful shock for me. However for this weblog put up, we’ll persist with the essential objects of hyperlink, deal with, route, and neigh.

The place within the community are we? Exploring “ip deal with”

First up in our exploration would be the “ip deal with” object. Reasonably than simply undergo the complete command assist or man web page line (guaranteeing nobody ever reads one other put up of mine), I’m going to have a look at some widespread issues I’d need to know concerning the community configuration on a bunch. As you’re exploring by yourself, I’d extremely advocate exploring “ip deal with assist” in addition to “man ip deal with” for extra particulars.  These instructions are very highly effective and versatile.

What’s my IP deal with?

(essential) skilled@expert-cws:~$ ip deal with present
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    hyperlink/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet scope host lo
       valid_lft ceaselessly preferred_lft ceaselessly
    inet6 ::1/128 scope host 
       valid_lft ceaselessly preferred_lft ceaselessly
2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    hyperlink/ether 00:0c:29:75:99:27 brd ff:ff:ff:ff:ff:ff
    inet brd scope world dynamic ens160
       valid_lft 1344sec preferred_lft 1344sec
    inet6 fe80::20c:29ff:fe75:9927/64 scope hyperlink 
       valid_lft ceaselessly preferred_lft ceaselessly
3: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default 
    hyperlink/ether 02:42:9a:0c:8a:ee brd ff:ff:ff:ff:ff:ff
    inet brd scope world docker0
       valid_lft ceaselessly preferred_lft ceaselessly

Operating “ip deal with present” will show the deal with configuration for all interfaces on the Linux workstation. My workstation has 3 interfaces configured, a loopback deal with, the ethernet interface, and docker interface. A number of the Linux hosts I work on have dozens of interfaces, notably if the host occurs to be operating a number of Docker containers as every container generates community interfaces. I plan to dive into Docker networking in future weblog posts, so we’ll depart the “docker0” interface alone for now.

We are able to focus our exploration by offering a selected community machine title as a part of our command.

(essential) skilled@expert-cws:~$ ip add present dev ens160
2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    hyperlink/ether 00:0c:29:75:99:27 brd ff:ff:ff:ff:ff:ff
    inet brd scope world dynamic ens160
       valid_lft 1740sec preferred_lft 1740sec
    inet6 fe80::20c:29ff:fe75:9927/64 scope hyperlink 
       valid_lft ceaselessly preferred_lft ceaselessly

Okay, that’s actually what I used to be inquisitive about once I wished to know what my IP deal with was. However there’s much more information in that output than simply the IP deal with. For a very long time, I simply skimmed over the output. I’d ignore most output and easily have a look at the deal with and for state information like “UP” or “DOWN.” Finally, I wished to know what all that output meant, so in case you’re inquisitive about easy methods to decode the output above…

  • Bodily interface particulars
    • “ens160” – The title of the interface from the working system’s perspective.  This relies rather a lot on the precise distribution of Linux you’re operating, whether or not it’s a digital or bodily machine, and the kind of interface.  Should you’re extra used to seeing “eth0” interface names (like I used to be) it’s time to turn out to be snug with the new interface naming scheme.
    • “<BROADCAST,MULTICAST,UP,LOWER_UP>” – Between the angle brackets are a collection of flags that present particulars concerning the interface state.  This reveals that my interface is each broadcast and multicast succesful and that the interface is enabled (UP) and that the bodily layer is related (LOWER_UP)
    • “mtu 1500” – The utmost transmission unit (MTU) for the interface.  This interface is configured for the default 1500 bytes
    • “qdisc mq” – This means the queueing method being utilized by the interface.  Issues to search for listed below are values of “noqueue” (ship instantly) or “noop” (drop all). There are a number of different choices for queuing a system is perhaps operating.
    • “state UP”- One other indication of the operational state of an interface.  “UP” and “DOWN” are fairly clear, however you may also see “UNKNOWN” like within the loopback interface above.  “UNKNOWN” signifies that the interface is up and operational, however nothing is related.  Which is fairly legitimate for a loopback deal with.
    • “group default” – Interfaces will be grouped collectively on Linux to permit widespread attributes or instructions.  Having all interfaces related to “group default” is the most typical setup, however there are some useful issues you are able to do for those who group interfaces collectively.  For instance, think about a VM host system with 2 interfaces for administration and eight for knowledge visitors.  You can group them into “mgmt” and “knowledge” teams after which management all interfaces of a sort collectively.
    • “qlen 1000” – The interface has a 1000 packet queue.  The 1001st packet can be dropped.
  • “hyperlink/ether” – The layer 2 deal with (MAC deal with) of the interface
  • “inet” – The IPv4 interface configuration
    • “scope world” – This deal with is globally reachable. Different choices embrace hyperlink and host
    • “dynamic” – This IP deal with was assigned by DHCP.  The lease size is listed within the subsequent line underneath “valid_lft”
    • “ens160” – A reference again to the interface this IP deal with is related to
  • “inet6” – The IPv6 interface configuration.  Solely the hyperlink native deal with is configured on the host.  This reveals that whereas IPv6 is enabled, the community doesn’t look to have it configured extra extensively

Community engineers hyperlink the world collectively one machine at a time. Exploring the “ip hyperlink” command.

Now that we’ve gotten our toes moist, let’s circle again to the “hyperlink” object. The output of “ip deal with present” command gave a little bit of a touch at what “hyperlink” is referring to. “Hyperlinks” are the community units configured on a bunch, and the “ip hyperlink” command offers engineers choices for exploring and managing these units.

What networking interfaces are configured on my host?

(essential) skilled@expert-cws:~$ ip hyperlink present
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    hyperlink/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    hyperlink/ether 00:0c:29:75:99:27 brd ff:ff:ff:ff:ff:ff
3: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default 
    hyperlink/ether 02:42:9a:0c:8a:ee brd ff:ff:ff:ff:ff:ff

After exploring the output of “ip deal with present,” it shouldn’t come as a shock that there are 3 community interfaces/units configured on my host.  And a fast look will present the output from this command is all included within the output for “ip deal with present.”  Because of this, I virtually all the time simply use “ip deal with present” when seeking to discover the community state of a bunch.

Nevertheless, the “ip hyperlink” object is sort of helpful whenever you need to configure new interfaces on a bunch or change the configuration on an current interface. For instance, “ip hyperlink set” can change the MTU on an interface.

root@expert-cws:~# ip hyperlink set ens160 mtu 9000

root@expert-cws:~# ip hyperlink present dev ens160
2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP mode DEFAULT group default qlen 1000
    hyperlink/ether 00:0c:29:75:99:27 brd ff:ff:ff:ff:ff:ff

Notice 1: Altering community configuration settings requires administrative or “root” privileges.

Notice 2: The adjustments made utilizing the “set” command on an object are usually NOT maintained throughout system or service restarts. That is the equal of adjusting the “running-configuration” of a community machine. With a purpose to change the “startup-configuration” you have to edit the community configuration recordsdata for the Linux host.  Examine the small print for community configuration on your distribution of Linux (ie Ubuntu, RedHat, Debian, Raspbian, and many others.)

Is anybody else on the market? Exploring the “ip neigh” command

Networks are most helpful when different units are related and reachable by means of the community. The “ip neigh” command provides engineers a view on the different hosts related to the identical community. Particularly, it gives a have a look at, and management of, the ARP desk for the host.

Do I’ve an ARP entry for the host that I’m having hassle connecting to?

A typical drawback community engineers are known as on to assist is when one host can’t discuss to a different host.  If I had a nickel for each assist desk ticket I’ve labored on like this one, I’d have an terrible lot of nickels. Suppose my makes an attempt to ping a bunch on my identical native community with IP deal with are failing. Step one I’d take can be to see if I’ve been capable of study an ARP entry for this host.

(essential) skilled@expert-cws:~$ ping
PING ( 56(84) bytes of information.
--- ping statistics ---
3 packets transmitted, 0 obtained, 100% packet loss, time 2039ms

(essential) skilled@expert-cws:~$ ip neigh present dev ens160  FAILED dev ens160 lladdr 00:50:56:f0:11:04 STALE dev ens160 lladdr 00:50:56:e1:f7:8a STALE dev ens160 lladdr 8a:66:5a:b5:3f:65 REACHABLE

And the reply isn’t any. The try and ARP for “FAILED.”  Nevertheless, I can see that ARP usually is engaged on my community, as I’ve different “REACHABLE” addresses within the desk.

One other widespread use of the “ip neigh” command includes clearing out an ARP entry after altering the IP deal with configuration of one other host (or hosts). For instance, for those who change the router on a community, a bunch gained’t be capable to talk with it till the outdated ARP entry ages out and the system tries ARPing once more for a brand new deal with. Relying on the working system, this may take minutes — which may really feel like years when ready for a system to begin responding once more. The “ip neigh flush” command can clear an entry from the desk instantly.

How do I get from right here to there? Exploring the “ip route” command

A lot of the visitors from a bunch is destined someplace on one other layer 3 community, and the host must know easy methods to “route” that visitors accurately. After trying on the IP deal with(es) configured on a bunch, I’ll usually check out the routing desk to see if it appears like I’d anticipate. For that, the “ip route” command is the primary place I look.

What routes does this host have configured?

(essential) skilled@expert-cws:~$ ip route present
default through dev ens160 proto dhcp src metric 100 through dev ens160 dev ens160 proto kernel scope hyperlink src dev docker0 proto kernel scope hyperlink src linkdown 

It could not look precisely just like the output of “present ip route” on a router, however this command offers very usable output.

  • My default gateway is by means of the “ens160” machine.  This route was realized from DHCP and can use the IP deal with configured on my “ens160” interface.
  • There’s a static route configured to community by means of deal with
  • And there are 2 routes that have been added by the kernel for the native community of the 2 configured IP addresses on the interfaces.  However the “docker0” route reveals “linkdown” — matching the state of the “docker0” interface we noticed earlier.

The “ip route” command will also be used so as to add or delete routes from the desk, however with the identical notes as after we used “ip hyperlink” to vary the MTU of an interface. You’ll want admin rights to run the command, and any adjustments made won’t be maintained after a restart. However this may nonetheless be very useful when troubleshooting or working within the lab.

And performed… or am I?

In order that’s is my “temporary” have a look at the “ip” command for Linux. Oh wait, that dangerous pun try jogged my memory of yet one more tip I meant to incorporate. There’s a “–temporary” possibility you’ll be able to add to any of the instructions that reformats the information in a pleasant desk that’s usually fairly useful. Listed below are a number of examples.

(essential) skilled@expert-cws:~$ ip --brief deal with present
lo               UNKNOWN ::1/128 
ens160           UP    fe80::20c:29ff:fe75:9927/64 
docker0          DOWN  

(essential) skilled@expert-cws:~$ ip --brief hyperlink present
lo               UNKNOWN        00:00:00:00:00:00 <LOOPBACK,UP,LOWER_UP> 
ens160           UP             00:0c:29:75:99:27 <BROADCAST,MULTICAST,UP,LOWER_UP> 
docker0          DOWN           02:42:9a:0c:8a:ee <NO-CARRIER,BROADCAST,MULTICAST,UP> 

Not all instructions have a “temporary” output model, however a number of do, and they’re price testing.

There may be fairly a bit extra I may go into on how you should use the “ip” command as a part of your Linux community administration skillset. (Checkout the “–json” flag for an additional nice possibility). However at 3,000+ phrases on this put up, I’m going to name it performed for right this moment. Should you’re inquisitive about a deeper have a look at Linux networking expertise like this, let me know, and I’ll come again for some follow-ups.

Listed below are some useful hyperlinks associated to what we mentioned right this moment.

  • Should you’re searching for a Linux VM to begin together with your exploration of any Linux matter, try the Candidate Workstation revealed for the DevNet Skilled lab examination. It’s an Ubuntu primarily based VM that has been setup to be able to go for community programmability subjects.  Even for those who aren’t finding out for the Skilled examination, it’s an incredible ready-to-use Linux VM.
  • Listed below are man web page hyperlinks for the instructions we checked out right this moment:
  • RedHat has a extremely useful “ip Command Cheatsheet

Let me know what you consider this put up and what you may like me to deal with in future posts. Depart a remark beneath or discover me over on Twitter @hfpreston. Till subsequent time!


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