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Packet capture in Clabernetes#

It is quite interesting to see how Clabernetes uses different datapath stitching tricks to connect lab nodes running in different containers. Sometimes looking at the packets exchanged between the nodes can help to understand the inner workings of the setup and often comes in handy when troubleshooting.

Capturing packets in Clabernetes is similar to capturing packets in Containerlab, with just one more indirection level added. Check the basics of packet capture in Containerlab to get started, because we will use the same technique here.

Capture script#

The most straightforward way to capture packets in Clabernetes is to leverage the capture script similar to the one we did for Containerlab, but instead of using ip netns exec we will use kubectl exec to run the packet capture in the container and piping the output to Wireshark.

Below you will find two script variants, one for a case when kubectl runs on the same machine where Wireshark is installer, and the second one when the kubectl runs on a remote machine.


The examples below are given for the MacOs, for Windows users running WSL the path to the Wireshark will be /mnt/c/Program\ Files/Wireshark/wireshark.exe and Linux users will figure it out without hints 😉

Since the kubectl is installed locally, we can straight away use kubectl exec to connect to the pod. The script below is used like:

bash <k8s-namespace> <pod name> <interface name>

kubectl exec -n $1 -it $2 -- tcpdump -U -nni $3 -w - | \
/Applications/ -k -i -

Since the kubectl is installed remotely, we need to use ssh to connect to the remote machine first. The script below is used like:

bash <host-with-kubectl> <k8s-namespace> <pod name> <interface name>

ssh $1 "kubectl exec -n $2 -it $3 -- tcpdump -U -nni $4 -w -" | \
/Applications/ -k -i -

It is a smart idea to save the script in a directory that is in your PATH so that you can run it from anywhere anytime you need to capture some packets.