Friday, February 24, 2023
HomeCloud ComputingExploring the Linux 'ip' Command

Exploring the Linux ‘ip’ Command

I’ve been speaking for a number of years now about how community engineers have to turn out to be comfy with Linux. I usually place it that we don’t all have to turn out to be “large bushy beard-bearing sysadmins.” Quite, community engineers should be capable of 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 (should you’d like a deeper exploration of that matter, please let me know). Nope… I wish to dive into a particular 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 accustomed to “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 targeted on community engineering and earned his CCNA for the primary time, he used the “ipconfig” command fairly usually whereas supporting Home windows desktop programs.

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 excellent a part of my toolkit. I’m really smiling in nostalgia as I sort this paragraph. ????

For previous instances’ sake, I requested John Capobianco, certainly one of 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 person nonetheless, whereas I transformed to Mac a few years in the past. And right here is the output of certainly one of my favourite Home windows instructions (edited for some privateness information).

Home windows IP Configuration

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

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : house
   Description . . . . . . . . . . . : Intel(R) Ethernet Connection (12) I219-V
   Bodily Tackle. . . . . . . . . : 24-4Q-FE-88-HH-XY
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure
   Hyperlink-local IPv6 Tackle . . . . . : fe80::31fa:60u2:bc09:qq45percent13(Most well-liked)
   IPv4 Tackle. . . . . . . . . . . : 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 Tackle. . . . . . . . . : 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 System (Private Space Community)
   Bodily Tackle. . . . . . . . . : C8-E2-65-A7-ER-Z8
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure

It’s nonetheless such an excellent and useful command. Just a few new issues in there from after I was utilizing it each day (IPv6, WiFi, Bluetooth), nevertheless it nonetheless appears to be like like I keep 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 thing was totally different, and it was ALL command line. I’m not ashamed to confess that I used to be a little bit intimidated. However then I discovered the command “ifconfig,” and I started to breathe a little bit simpler. The output didn’t look the identical, however the command itself was shut. The knowledge 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 Knowledgeable 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) professional@expert-cws:~$ ifconfig

Command 'ifconfig' not discovered, however could 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 not one of the best command for viewing the community interface configuration in Linux. In reality, it hasn’t been the “greatest command” for a very long time. At present the “ip” command is what we needs to be utilizing.  I’ve recognized this for some time, however giving up one thing that made you’re feeling comfy and secure 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 a lot 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 already know what, it’s a very nice command. The “ip” command is way extra highly effective than “ifconfig.”

When I discovered myself fascinated by a subject for a weblog put up, I figured there is perhaps one other engineer or two on the market who may respect 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) professional@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 a little bit higher after 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 it’s essential to discover or change the community configuration. Let’s stroll by a little bit of “networking 101” with the “ip” command.

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

(essential) professional@expert-cws:~$ ip
Utilization: ip [ OPTIONS ] OBJECT  assist 
       ip [ -force ] -batch filename
the place  OBJECT :=  l2tp 
       OPTIONS := { -V[ersion] | -s[tatistics] | -d[etails] | -r[esolve] |
                    -h[uman-readable] | -iec | -j[son] | -p[retty] |
                    -f[amily]  inet6  |
                    -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] identify | -N[umeric] | -a[ll] |

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

  • hyperlink – I’m curious what “hyperlink” means on this context, nevertheless it catches my eye for certain
  • deal with – That is actually promising. The ip “addresses” assigned to a bunch is excessive on the listing of issues I do know I’ll wish 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 fascinated with.
  • neigh – Neighbors? What sort of neighbors?
  • tunnel – Oooo… tunnel interfaces are undoubtedly attention-grabbing to see right here.
  • maddress, mroute, mrule – My preliminary thought after I noticed “maddress” was “MAC deal with,” however then I seemed 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 listing are attention-grabbing to see. Having “netconf” within the listing 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. Quite than simply undergo the total command assist or man web page line (making certain nobody ever reads one other put up of mine), I’m going to take a look at some widespread issues I’d wish to know concerning the community configuration on a bunch. As you’re exploring by yourself, I might extremely suggest 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) professional@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

Working “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 few 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 particular community system identify as a part of our command.

(essential) professional@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 fascinated with after I needed 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 might ignore most output and easily have a look at the deal with and for state information like “UP” or “DOWN.” Finally, I needed to know what all that output meant, so in case you’re fascinated with how one can decode the output above…

  • Bodily interface particulars
    • “ens160” – The identify of the interface from the working system’s perspective.  This relies lots on the particular 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 comfy 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 strategy being utilized by the interface.  Issues to search for listed here 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 additionally 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 could be grouped collectively on Linux to permit widespread attributes or instructions.  Having all interfaces related to “group default” is the commonest setup, however there are some useful issues you are able to do should you group interfaces collectively.  For instance, think about a VM host system with 2 interfaces for administration and eight for information visitors.  You could possibly group them into “mgmt” and “information” teams after which management all interfaces of a sort collectively.
    • “qlen 1000” – The interface has a 1000 packet queue.  The 1001st packet could 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 embody hyperlink and host
    • “dynamic” – This IP deal with was assigned by DHCP.  The lease size is listed within the subsequent line beneath “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 broadly

Community engineers hyperlink the world collectively one system 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) professional@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.”  For that reason, I nearly at all times simply use “ip deal with present” when seeking to discover the community state of a bunch.

Nonetheless, the “ip hyperlink” object is kind of helpful if you wish 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

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

Word 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 system. So as to change the “startup-configuration” it’s essential to edit the community configuration recordsdata for the Linux host.  Test the small print for community configuration in your distribution of Linux (ie Ubuntu, RedHat, Debian, Raspbian, and so on.)

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

Networks are most helpful when different units are related and reachable by the community. The “ip neigh” command offers 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 bother connecting to?

A standard drawback community engineers are known as on to help is when one host can’t speak 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 similar native community with IP deal with are failing. Step one I’d take could be to see if I’ve been in a position to study an ARP entry for this host.

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

(essential) professional@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 is not any. The try to ARP for “FAILED.”  Nonetheless, I can see that ARP basically 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, should you change the router on a community, a bunch gained’t be capable of talk with it till the previous 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

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

What routes does this host have configured?

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

It might 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 the “ens160” system.  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 deal with
  • And there are 2 routes that had 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 completed… 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 another tip I meant to incorporate. There’s a “–temporary” choice you may add to any of the instructions that reformats the info in a pleasant desk that’s usually fairly useful. Listed below are just a few examples.

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

(essential) professional@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 value trying out.

There’s fairly a bit extra I may go into on how you should utilize the “ip” command as a part of your Linux community administration skillset. (Checkout the “–json” flag for an additional nice choice). However at 3,000+ phrases on this put up, I’m going to name it completed for right this moment. Should you’re fascinated with a deeper have a look at Linux networking abilities 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 printed for the DevNet Knowledgeable lab examination. It’s an Ubuntu primarily based VM that has been setup to be able to go for community programmability subjects.  Even should you aren’t finding out for the Knowledgeable examination, it’s an excellent ready-to-use Linux VM.
  • Listed below are man web page hyperlinks for the instructions we checked out right this moment:
  • RedHat has a very useful “ip Command Cheatsheet

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


Observe Cisco Studying & Certifications

TwitterFbLinkedIn | Instagram



Most Popular