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 “huge bushy beard-bearing sysadmins.” Fairly, 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 (in the event you’d like a deeper exploration of that matter, please let me know). Nope… I need 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 might be accustomed to “ipconfig” on Home windows. The “ipconfig” command supplies particulars in regards to 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 repeatedly whereas supporting Home windows desktop techniques.
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 really smiling in nostalgia as I sort this paragraph. 🙂
For previous occasions’ sake, I requested John Capobianco, considered 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 considered 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. . . . . . : instance.com Ethernet adapter Ethernet: Connection-specific DNS Suffix . : dwelling 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 well-liked) IPv4 Deal with. . . . . . . . . . . : 192.168.122.36(Most well-liked) Subnet Masks . . . . . . . . . . . : 255.255.255.0 Lease Obtained. . . . . . . . . . : July 22, 2022 8:30:42 AM Lease Expires . . . . . . . . . . : July 25, 2022 8:30:41 AM Default Gateway . . . . . . . . . : 192.168.2.1 DHCP Server . . . . . . . . . . . : 192.168.2.1 DHCPv6 IAID . . . . . . . . . . . : 203705342 DHCPv6 Shopper DUID. . . . . . . . : 00-01-00-01-27-7B-B2-1D-24-4Q-FE-88-HH-XY DNS Servers . . . . . . . . . . . : 192.168.122.1 NetBIOS over Tcpip. . . . . . . . : Enabled Wi-fi LAN adapter Wi-Fi: Media State . . . . . . . . . . . : Media disconnected Connection-specific DNS Suffix . : dwelling 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 Machine (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 useful command. A couple of new issues in there from after I was utilizing it every day (IPv6, WiFi, Bluetooth), but it surely 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. All the things was totally different, and it was ALL command line. I’m not ashamed to confess that I used to be a bit intimidated. However then I discovered the command “ifconfig,” and I started to breathe a bit 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.”
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 instance, I used to be offered with this output.
(essential) 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 the most effective command for viewing the community interface configuration in Linux. In truth, it hasn’t been the “greatest command” for a very long time. Right now the “ip” command is what we ought to be utilizing. I’ve identified this for some time, however giving up one thing that made you’re feeling snug 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 much 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. You understand what, it’s a very nice command. The “ip” command is way extra highly effective than “ifconfig.”
When I discovered myself fascinated with a subject for a weblog put up, I figured there could be 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 go away 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 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
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 172.16.211.128 netmask 255.255.255.0 broadcast 172.16.211.255
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 127.0.0.1 netmask 255.0.0.0
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 a bit higher after I began working with Linux.
Exploring the IP configuration of your Linux host with the “ip” command!
So there you might be, a community engineer sitting on the console of a Linux workstation, and it’s good to discover or change the community configuration. Let’s stroll via a little bit of “networking 101” with the “ip” command.
First up, let’s see what occurs once we simply run “ip.”
(essential) professional@expert-cws:~$ ip
Utilization: ip [ OPTIONS ] OBJECT assist
ip [ -force ] -batch filename
the place OBJECT := netconf
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] |
-c[olor]}
There’s some fascinating information simply on this assist/utilization message. It appears like “ip” requires an OBJECT on which a COMMAND is executed. And the doable objects embody a number of that bounce out on the community engineer inside me.
- hyperlink – I’m curious what “hyperlink” means on this context, but it surely 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 considering when it comes to the “ipconfig” or “ifconfig” command. However the routes configured on a bunch is one thing I’ll be focused on.
- neigh – Neighbors? What sort of neighbors?
- tunnel – Oooo… tunnel interfaces are undoubtedly fascinating 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 go away “multicast” for an additional weblog put up. 🙂
The opposite objects within the checklist are fascinating to see. Having “netconf” within the checklist was a cheerful shock for me. However for this weblog put up, we’ll keep on 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. Fairly than simply undergo the complete command assist or man web page line (making certain nobody ever reads one other put up of mine), I’m going to have a look at some widespread issues I would need to know in regards to the community configuration on a bunch. As you might be exploring by yourself, I’d 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 127.0.0.1/8 scope host lo
valid_lft without end preferred_lft without end
inet6 ::1/128 scope host
valid_lft without end preferred_lft without end
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 172.16.211.128/24 brd 172.16.211.255 scope international dynamic ens160
valid_lft 1344sec preferred_lft 1344sec
inet6 fe80::20c:29ff:fe75:9927/64 scope hyperlink
valid_lft without end preferred_lft without end
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 172.17.0.1/16 brd 172.17.255.255 scope international docker0
valid_lft without end preferred_lft without end
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 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 go away 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 172.16.211.128/24 brd 172.16.211.255 scope international dynamic ens160
valid_lft 1740sec preferred_lft 1740sec
inet6 fe80::20c:29ff:fe75:9927/64 scope hyperlink
valid_lft without end preferred_lft without end
Okay, that’s actually what I used to be focused on after I wished to know what my IP deal with was. However there may be 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 focused on easy methods to decode the output above…
- Bodily interface particulars
- “ens160” – The identify of the interface from the working system’s perspective. This relies so much on the particular distribution of Linux you might be operating, whether or not it’s a digital or bodily machine, and the kind of interface. When 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 in regards to the interface state. This exhibits 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 below 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 related. Which is fairly legitimate for a loopback deal with.
- “group default” – Interfaces may 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 in the event you group interfaces collectively. For instance, think about a VM host system with 2 interfaces for administration and eight for information visitors. You can 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 can be dropped.
- “hyperlink/ether” – The layer 2 deal with (MAC deal with) of the interface
- “inet” – The IPv4 interface configuration
- “scope international” – 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 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 exhibits 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 ft 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 gadgets configured on a bunch, and the “ip hyperlink” command supplies engineers choices for exploring and managing these gadgets.
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/gadgets 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.
Nonetheless, the “ip hyperlink” object is sort of helpful if you want 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 modifications made utilizing the “set” command on an object are usually NOT maintained throughout system or service restarts. That is the equal of fixing the “running-configuration” of a community system. As a way to change the “startup-configuration” it’s good to edit the community configuration information for the Linux host. Test the main points for community configuration in 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 gadgets are related and reachable via the community. The “ip neigh” command provides engineers a view on the different hosts related 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 bother 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 bunch on my similar native community with IP deal with 172.16.211.30 are failing. Step one I would take can be to see if I’ve been capable of be taught an ARP entry for this host.
(essential) professional@expert-cws:~$ ping 172.16.211.30 PING 172.16.211.30 (172.16.211.30) 56(84) bytes of knowledge. ^C --- 172.16.211.30 ping statistics --- 3 packets transmitted, 0 obtained, 100% packet loss, time 2039ms (essential) professional@expert-cws:~$ ip neigh present 172.16.211.30 dev ens160 FAILED 172.16.211.254 dev ens160 lladdr 00:50:56:f0:11:04 STALE 172.16.211.2 dev ens160 lladdr 00:50:56:e1:f7:8a STALE 172.16.211.1 dev ens160 lladdr 8a:66:5a:b5:3f:65 REACHABLE
And the reply isn’t any. The try and ARP for 172.16.211.30 “FAILED.” Nonetheless, I can see that ARP on the whole is engaged on my community, as I’ve different “REACHABLE” addresses within the desk.
One other widespread use of the “ip neigh” command entails clearing out an ARP entry after altering the IP deal with configuration of one other host (or hosts). For instance, in the event you substitute the router on a community, a bunch received’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 could take minutes — which may 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 bunch is destined someplace on one other layer 3 community, and the host must know easy methods to “route” that visitors accurately. After wanting on the IP deal with(es) configured on a bunch, I’ll typically check out the routing desk to see if it appears 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 through 172.16.211.2 dev ens160 proto dhcp src 172.16.211.128 metric 100 10.233.44.0/23 through 172.16.211.130 dev ens160 172.16.211.0/24 dev ens160 proto kernel scope hyperlink src 172.16.211.128 172.17.0.0/16 dev docker0 proto kernel scope hyperlink src 172.17.0.1 linkdown
It could not look precisely just like the output of “present ip route” on a router, however this command supplies very usable output.
- My default gateway is 172.16.211.2 via 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 10.233.44.0/23 via deal with 172.16.211.130
- 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 exhibits “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 vary the MTU of an interface. You’ll want admin rights to run the command, and any modifications made is not going to be maintained after a restart. However this could nonetheless be very useful when troubleshooting or working within the lab.
And carried out… or am I?
In order that’s is my “transient” have a look at the “ip” command for Linux. Oh wait, that dangerous pun try jogged my memory of yet another tip I meant to incorporate. There’s a “–transient” possibility you may add to any of the instructions that reformats the information in a pleasant desk that’s typically fairly useful. Listed below are a number of examples.
(essential) professional@expert-cws:~$ ip --brief deal with present lo UNKNOWN 127.0.0.1/8 ::1/128 ens160 UP 172.16.211.128/24 fe80::20c:29ff:fe75:9927/64 docker0 DOWN 172.17.0.1/16 (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 “transient” output model, however a number of do, and they’re value trying out.
There may be fairly a bit extra I may go into on how you need to 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 carried out for right this moment. When you’re focused on 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.
- When you’re in search of a Linux VM to start out together with your exploration of any Linux matter, take a look at the Candidate Workstation revealed for the DevNet Skilled lab examination. It’s an Ubuntu based mostly VM that has been setup to be able to go for community programmability matters. Even in the event you aren’t finding out 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 right this moment:
- RedHat has a extremely useful “ip Command Cheatsheet”
Let me know what you concentrate on this put up and what you may like me to sort out in future posts. Depart a remark under or discover me over on Twitter @hfpreston. Till subsequent time!
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