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HomeHealth NewsExploring 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 change into comfy with Linux. I usually place it that we don’t all have to change into “massive bushy beard-bearing sysadmins.” Slightly, community engineers should have the ability 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 (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 truth (or two)

If you’re like me and began your computing world on a Home windows machine, perhaps you’re acquainted with “ipconfig” on Home windows. The “ipconfig” command offers particulars in regards to 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 often 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 individual.)

It was an awesome a part of my toolkit. I’m truly smiling in nostalgia as I sort this paragraph. 🙂

For outdated occasions’ sake, I requested John Capobianco, one in all my latest co-workers right here at Cisco Studying & Certifications, to ship me the output from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 Identify . . . . . . . . . . . . : WINROCKS
   Main 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 Deal with. . . . . . . . . : 24-4Q-FE-88-HH-XY
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure
   Hyperlink-local IPv6 Deal with . . . . . : fe80::31fa:60u2:bc09:qq45percent13(Most popular)
   IPv4 Deal with. . . . . . . . . . . : popular)
   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 Shopper 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 Deal with. . . . . . . . . : 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 Gadget (Private Space Community)
   Bodily Deal with. . . . . . . . . : C8-E2-65-A7-ER-Z8
   DHCP Enabled. . . . . . . . . . . : Sure
   Autoconfiguration Enabled . . . . : Sure

It’s nonetheless such an awesome and helpful command. Just a few new issues in there from once I was utilizing it day by day (IPv6, WiFi, Bluetooth), however 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. The whole lot was completely 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 simple sufficient to learn. So, I gained a little bit of confidence and knew, “I can do that.”

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

(major) professional@expert-cws:~$ ifconfig

Command 'ifconfig' not discovered, however may 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 one of the best command for viewing the community interface configuration in Linux. In truth, it hasn’t been the “greatest command” for a very long time. In the present day the “ip” command is what we ought to be utilizing.  I’ve recognized this for some time, however giving up one thing that made you are feeling comfy and protected is tough. 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 spotted that I wanted to get with the occasions. I began utilizing the “ip” command on Linux. what, it’s a very nice command. The “ip” command is way extra highly effective than “ifconfig.”

When I discovered myself desirous about a subject for a weblog put up, I figured there could be one other engineer or two on the market who would possibly recognize a private introduction to the “ip” command from Hank.

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

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

(major) 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  service 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  service 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  service 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 it is advisable 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 once we simply run “ip.”

(major) professional@expert-cws:~$ ip
Utilization: ip [ OPTIONS ] OBJECT  assist 
       ip [ -force ] -batch filename
the place  OBJECT :=  addrlabel 
       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 attainable objects embody a number of that soar out on the community engineer inside me.

  • hyperlink – I’m curious what “hyperlink” means on this context, however it catches my eye for positive
  • tackle – That is actually promising. The ip “addresses” assigned to a number is excessive on the checklist 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 considering by way of the “ipconfig” or “ifconfig” command. However the routes configured on a number is one thing I’ll be concerned 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 once I noticed “maddress” was “MAC tackle,” however then I regarded on the subsequent two objects and thought perhaps it’s “multicast tackle.” We’ll go away “multicast” for one more 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 follow the essential objects of hyperlink, tackle, route, and neigh.

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

First up in our exploration would be the “ip tackle” object. Slightly 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 take a look at some frequent issues I would wish to know in regards to the community configuration on a number. As you’re exploring by yourself, I’d extremely advocate exploring “ip tackle assist” in addition to “man ip tackle” for extra particulars.  These instructions are very highly effective and versatile.

What’s my IP tackle?

(major) professional@expert-cws:~$ ip tackle 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 tackle present” will show the tackle configuration for all interfaces on the Linux workstation. My workstation has 3 interfaces configured, a loopback tackle, the ethernet interface, and docker interface. A few of the Linux hosts I work on have dozens of interfaces, significantly if the host occurs to be operating plenty of Docker containers as every container generates community interfaces. I plan to dive into Docker networking in future weblog posts, so we’ll go away the “docker0” interface alone for now.

We will focus our exploration by offering a particular community system identify as a part of our command.

(major) 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 concerned with once I needed to know what my IP tackle was. However there may be much more information in that output than simply the IP tackle. For a very long time, I simply skimmed over the output. I’d ignore most output and easily have a look at the tackle and for state information like “UP” or “DOWN.” Finally, I needed to know what all that output meant, so in case you’re concerned 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 quite a bit 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 change into comfy with the new interface naming scheme.
    • “<BROADCAST,MULTICAST,UP,LOWER_UP>” – Between the angle brackets are a collection of flags that present particulars in regards to 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 linked (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 could be 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 linked.  Which is fairly legitimate for a loopback tackle.
    • “group default” – Interfaces may be grouped collectively on Linux to permit frequent attributes or instructions.  Having all interfaces linked to “group default” is the commonest setup, however there are some helpful 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 might group them into “mgmt” and “information” teams after which management all interfaces of a kind collectively.
    • “qlen 1000” – The interface has a 1000 packet queue.  The 1001st packet could be dropped.
  • “hyperlink/ether” – The layer 2 tackle (MAC tackle) of the interface
  • “inet” – The IPv4 interface configuration
    • “scope world” – This tackle is globally reachable. Different choices embody hyperlink and host
    • “dynamic” – This IP tackle 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 tackle is related to
  • “inet6” – The IPv6 interface configuration.  Solely the hyperlink native tackle 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 system at a time. Exploring the “ip hyperlink” command.

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

What networking interfaces are configured on my host?

(major) 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 tackle 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 tackle present.”  For that reason, I virtually all the time simply use “ip tackle present” when seeking to discover the community state of a number.

Nonetheless, the “ip hyperlink” object is kind of helpful if you need to configure new interfaces on a number or change the configuration on an present 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

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

Observe 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. With a view to change the “startup-configuration” it is advisable edit the community configuration information for the Linux host.  Verify the main points for community configuration on your distribution of Linux (ie Ubuntu, RedHat, Debian, Raspbian, and so forth.)

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

Networks are most helpful when different units are linked and reachable by means of the community. The “ip neigh” command offers engineers a view on the different hosts linked to the identical community. Particularly, it provides 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 help 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 number on my identical native community with IP tackle are failing. Step one I would take could be to see if I’ve been capable of study an ARP entry for this host.

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

(major) 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 isn’t any. The try and ARP for “FAILED.”  Nonetheless, I can see that ARP typically is engaged on my community, as I’ve different “REACHABLE” addresses within the desk.

One other frequent use of the “ip neigh” command entails clearing out an ARP entry after altering the IP tackle configuration of one other host (or hosts). For instance, should you exchange the router on a community, a number gained’t have the ability to talk with it till the outdated ARP entry ages out and the system tries ARPing once more for a brand new tackle. Relying on the working system, this may take minutes — which might really feel like years when ready for a system to start out 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 number is destined someplace on one other layer 3 community, and the host must know how one can “route” that visitors accurately. After trying on the IP tackle(es) configured on a number, I’ll typically 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?

(major) professional@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 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 means of the “ens160” system.  This route was discovered from DHCP and can use the IP tackle configured on my “ens160” interface.
  • There’s a static route configured to community by means of tackle
  • 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 may also be used so as to add or delete routes from the desk, however with the identical notes as once we used “ip hyperlink” to alter 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 helpful when troubleshooting or working within the lab.

And accomplished… or am I?

In order that’s is my “transient” have a look at the “ip” command for Linux. Oh wait, that unhealthy pun try jogged my memory of yet another tip I meant to incorporate. There’s a “–transient” choice you may add to any of the instructions that reformats the information in a pleasant desk that’s typically fairly helpful. Listed below are a couple of examples.

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

(major) 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 “transient” output model, however a number of do, and they’re value trying out.

There may be fairly a bit extra I might go into on how you should utilize the “ip” command as a part of your Linux community administration skillset. (Checkout the “–json” flag for one more nice choice). However at 3,000+ phrases on this put up, I’m going to name it accomplished for at present. Should you’re concerned with 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 at present.

  • Should you’re on the lookout for a Linux VM to start out together with your exploration of any Linux matter, take a look at the Candidate Workstation printed 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 matters.  Even should you aren’t learning for the Skilled examination, it’s an awesome ready-to-use Linux VM.
  • Listed below are man web page hyperlinks for the instructions we checked out at present:
  • RedHat has a extremely helpful “ip Command Cheatsheet

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


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