How do you find the cluster & service CIDR of a Kubernetes cluster?

Question

How do you find the cluster/service CIDR for a Kubernetes cluster, once it is already running?

I know for Minikube, it is 10.0.0.1/24.

For GKE, you can find out via

gcloud container clusters describe XXXXXXX --zone=XXXXXX |
  grep -e clusterIpv4Cidr -e servicesIpv4Cidr

But how do you find out on a generic Kubernetes cluster, particularly via kubectl?

score 64 · Answer 1 · answered May 08 '20 at 18:41

64

I spent hours searching for a generic way to do this. I gave up searching and wrote my own. As of Kubernetes 1.18, this method works across cloud providers, beyond just GKE.

SVCRANGE=$(echo '{"apiVersion":"v1","kind":"Service","metadata":{"name":"tst"},"spec":{"clusterIP":"1.1.1.1","ports":[{"port":443}]}}' | kubectl apply -f - 2>&1 | sed 's/.*valid IPs is //')
echo $SVCRANGE
172.21.0.0/16

This one liner works by feeding an invalid service cluster IP into kubectl apply and parsing the error output, which provides the service CIDR information.

answered May 08 '20 at 18:41

Steven Dake

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Clean solution, and the only one that worked for me. – Anirudh May 18 '20 at 03:54
Thank you so much for the positive feedback! My first one on stack overflow :) If there is any way to improve the answer, please let me know. – Steven Dake May 23 '20 at 16:05
1

I lost access to "dump" and it was off hours, this helped me figure things out :) – Dejan Marjanović Jul 15 '20 at 23:52
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You are the MVP @StevenDake. I tried this on 1.14.9 and it works there as well. – Kiran Aug 25 '20 at 14:49
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Thnx. First answer didn't work for me, but this one did! Is there a similar way for finding cluster CIDR? (pod ip ranges) – Mohammad Yosefpor Oct 01 '20 at 19:58
Mohammad, I have looked around the various APIs for any form of pod IP input. I can't seem to find any. That doesn't mean one doesn't exist, but there are approximately 50 different APIs in K8s. If you find an API that accepts POD ips, I'll be happy to prototype. – Steven Dake Dec 31 '20 at 10:59

score 60 · Accepted Answer · answered Jan 14 '19 at 14:27

60

Get Services IPs range

kubectl cluster-info dump | grep -m 1 service-cluster-ip-range

You will see something like e.g. --service-cluster-ip-range=xxx.yy.0.0/13

Get Pods IPs range

kubectl cluster-info dump | grep -m 1 cluster-cidr

You will see something like e.g. --cluster-cidr=xxx.yy.0.0/11

answered Jan 14 '19 at 14:27

Vasilis Vasilatos

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doesn't work on DOKS ether – Abderrahim Soubai-Elidrisi Oct 12 '21 at 15:34
this did not work for me, probably because I let it use the default CIDRs and did not specify my own during `kubeadm init` – ComradeJoecool Nov 24 '21 at 16:15

score 7 · Answer 3 · answered May 26 '17 at 03:26

7

Did you check if the following command contains the info you need?

kubectl cluster-info dump

answered May 26 '17 at 03:26

Oswin Noetzelmann

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For me, `kubectl cluster-info dump | grep -i cidr` worked to find the pidCIDRs and the clusterCIDR. – damick Jun 27 '17 at 18:29
error: missing apiVersion or kind and cannot assign it; no kind is registered for the type core.NodeList – Breedly Sep 25 '18 at 13:58
This error exists in 1.11 and should be fixed in 1.12: https://github.com/kubernetes/kubernetes/issues/65221 – lanoxx Oct 09 '18 at 08:34
Doesn't work with all network plugins (I am using Canal) – leodotcloud Feb 27 '19 at 23:37

score 4 · Answer 4 · answered Oct 31 '20 at 16:42

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kubectl describe cm kubeadm-config -n kube-system |grep Subnet

answered Oct 31 '20 at 16:42

Marco Aurelio Miranda

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this did not work for me, probably because I let it use the default CIDRs and did not specify my own during `kubeadm init` – ComradeJoecool Nov 24 '21 at 16:14

score 2 · Answer 5 · answered Dec 24 '19 at 20:59

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With kubeadm

kubeadm config view | grep Subnet

Below output is self explanatory

podSubnet: 10.10.0.0/16

serviceSubnet: 10.96.0.0/12

answered Dec 24 '19 at 20:59

user3165768

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this did not work for me, probably because I let it use the default CIDRs and did not specify my own during `kubeadm init` – ComradeJoecool Nov 24 '21 at 16:12

score 2 · Answer 6 · answered Nov 13 '20 at 13:50

2

If you did not specify --pod-network-cidr or --service-cidr, the defaults are used. Get defaults:

kubeadm config print init-defaults

Or get the configmap:

kubectl  --namespace kube-system get configmap kubeadm-config -o yaml

answered Nov 13 '20 at 13:50

Moazzem Hossen

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Did not work for me. I did not specify a `--pod-network-cidr` during init and it was not listed in `kubeadm config print init-defaults` or `kubectl --namespace kube-system get configmap kubeadm-config -o yaml` – ComradeJoecool Nov 24 '21 at 16:11

score 1 · Answer 7 · answered Dec 07 '17 at 03:56

I can't leave a comment yet cause of rep so I'm just gonna answer with what I've found.

For minikube it looks like the CIDR can change, specifically for me it has. I found the CIDR under the .minikube directory at

.minikube\profiles\minikube

For windows you can find that at:

C:\Users\YourUserName\.minikube\profiles\minikube

For linux and mac I'd assume it would be under the ~/.minikube dir.

In the dir there should be a file called config.json which has a json object "KubernetesConfig": {} with the following field: ServiceCIDR. The value of that should be the CIDR for your services.

Unfortunately I have no other tips for kubectl to find the CIDR, maybe it's more of a provider thing and dependent on where/how you're running kubernetes.

score 0 · Answer 8 · answered Jun 15 '20 at 09:56

0

Similarly as proposed before, but with only the CIDR returned:

POD_CIDR=$(kubectl cluster-info dump | grep -m 1 -Po '(?<=--cluster-cidr=)[0-9.\/]+')
SERVICE_RANGE=$(kubectl cluster-info dump | grep -m 1 -Po '(?<=--service-cluster-ip-range=)[0-9.\/]+')

answered Jun 15 '20 at 09:56

palexster

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this did not work for me, probably because I let it use the default CIDRs and did not specify my own during `kubeadm init` – ComradeJoecool Nov 24 '21 at 16:13

score 0 · Answer 9 · answered Jun 14 '23 at 17:50

0

All of this answers/solution didn't work in my case.

And this is what worked for me and it's yet another way to see the All POD CIDRs used.

kubectl describe node | egrep 'PodCIDR|Name:'

Name: is so you identify the Node name too.

answered Jun 14 '23 at 17:50

ashokrajar

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How do you find the cluster & service CIDR of a Kubernetes cluster?

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