Network Troubleshooting on Linux

Network troubleshooting can be complicated depends on what tool and restriction on the environment. List some common commands for debugging network connectivity.

Netshoot

Netshoot is a handy docker image packed with all kinds of tools for debugging network, especially in a docker / kubernetes environment.

apiVersion: v1
kind: Pod
metadata:
  name: netshoot
  namespace: default
spec:
  containers:
  - name: netshoot
    image: nicolaka/netshoot
    command:
      - sleep
      - "infinity"
    imagePullPolicy: IfNotPresent
  restartPolicy: Always

Commands

ip

ip address
ip link
ip addr
ifconfig
arp

dns

/etc/hosts: local DNS record

/etc/resolv.conf: DNS server location

/etc/nsswitch.conf: change DNS resolve order

dig www.google.com
nslookup www.google.com
host www.google.com

# operating system name
uname 

# host system name
hostname

Check local process and its listening port

sudo lsof -iTCP -sTCP:LISTEN -n -P

openssl

# view website certificate
openssl s_client -showcerts -connect www.cisco.com:443

curl

# skip ssl verification, add log, auto redirect
curl -kvvv -L google.com

# custom ca cert
curl --cacert ./cacert.pem google.com

# telnet protocol
curl telnet://192.168.11.2:22