Linux Networking Troubleshooting — Mac Minis + M1¶

The Goal¶

Find IPs of Debian minis (ethernet or Tailscale)
Confirm connectivity between M1 and minis
Diagnose when things aren't reachable

1. Finding IP Addresses¶

On the Debian minis¶

# List all interfaces and their IPs
ip addr show

# Short version — just IPs
ip -brief addr show

# Specific interface (ethernet is usually eth0, enp2s0, or similar)
ip addr show eth0

# If you don't know the interface name
ip link show
# Look for the non-loopback interface (not 'lo')

Sample output to read:

2: enp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP>
    inet 192.168.1.42/24 brd 192.168.1.255 scope global enp2s0

inet 192.168.1.42 = that's your IP.

On M1 macOS¶

# List interfaces
ifconfig

# Just the relevant one (ethernet via adapter usually en3 or en5, WiFi is en0)
ifconfig en0

# Cleaner — specific interface
ipconfig getifaddr en0

# Find all IPs across all interfaces
ifconfig | grep "inet " | grep -v 127.0.0.1

Tailscale IPs¶

# On any node with Tailscale installed
tailscale ip -4

# Status of all Tailscale peers
tailscale status

2. Checking Connectivity¶

# Basic ping — is the host reachable?
ping <ip>

# Limit to 4 packets
ping -c 4 <ip>

# Check if a specific port is open (e.g. SSH on 22, k8s API on 6443)
nc -zv <ip> 22
nc -zv <ip> 6443

# Or with curl for HTTP
curl -v http://<ip>:<port>

3. Routing¶

# Show routing table — where does traffic go?
ip route show

# Which interface/gateway handles traffic to a specific IP?
ip route get <destination-ip>

4. DNS¶

# Resolve a hostname
nslookup <hostname>
dig <hostname>

# Quick check
host <hostname>

# What DNS server is being used?
cat /etc/resolv.conf

5. Checking Listening Ports¶

# What's listening on which port?
ss -tlnp

# Or with netstat (older systems)
netstat -tlnp

# Is something listening on port 6443 (k8s API)?
ss -tlnp | grep 6443

6. Firewall¶

# Check iptables rules (will be extensive on a k8s node)
sudo iptables -L -n

# Check ufw status (simpler firewall frontend)
sudo ufw status

# Check if firewalld is running
sudo systemctl status firewalld

7. Interface Up/Down¶

# Bring an interface up
sudo ip link set eth0 up

# Bring it down
sudo ip link set eth0 down

# Restart networking service (Debian)
sudo systemctl restart networking

8. SSH Connectivity (M1 → Minis)¶

# Basic SSH
ssh user@<mini-ip>

# Via Tailscale
ssh user@<tailscale-ip>

# With verbose output (debug connection issues)
ssh -v user@<mini-ip>

# Copy files M1 → mini
scp localfile user@<mini-ip>:/remote/path

# Copy files mini → M1
scp user@<mini-ip>:/remote/path ./localpath

9. Common Problems + Fixes¶

Symptom	Likely cause	Check
Can't ping mini from M1	Not on same network / firewall	`ip route show` on mini, check default gateway
SSH connection refused	SSH not running	`sudo systemctl status ssh` on mini
SSH timeout	Firewall blocking port 22	`sudo ufw status` or `ss -tlnp \\| grep 22`
Tailscale peer not reachable	Not logged in / not running	`tailscale status` on both machines
Wrong IP showing	DHCP lease changed	Set static IPs (see below)

10. Setting a Static IP on Debian¶

Edit /etc/network/interfaces:

auto enp2s0
iface enp2s0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 8.8.8.8

Then restart:

sudo systemctl restart networking

Recommended: set static IPs on both minis before kubeadm init.
DHCP changing IPs after cluster setup = things break.

11. Useful One-liners¶

# Who else is on my network?
sudo arp-scan --localnet        # needs arp-scan installed
arp -a                          # ARP cache (partial view)

# Trace route to a host
traceroute <ip>

# Check interface stats (errors, drops)
ip -s link show eth0

# Watch live network traffic on an interface
sudo tcpdump -i eth0 -n

# Watch traffic to/from a specific IP
sudo tcpdump -i eth0 host <ip>