Network Configuration | Jungle Scripts

Network Commands

Networking issues are among the most common production incidents. The fastest way to debug is to follow a consistent checklist: link → IP → route → DNS → ports → firewall.

$ ip addr # Show IP addresses
$ ip route # Show routing table
$ ip link # Interface state (UP/DOWN)
$ ss -tuln # Show listening ports
$ ping google.com
$ traceroute google.com
$ dig google.com # DNS lookup

Quick Connectivity Tests

# Is DNS the problem?
$ ping -c 1 8.8.8.8
$ ping -c 1 google.com

# Can we reach a port?
$ nc -vz example.com 443
$ curl -I https://example.com

# What is listening locally?
$ ss -tulpn | head

DNS on Modern Linux

DNS can involve multiple layers (systemd-resolved, NetworkManager, resolvconf). If name resolution is flaky, inspect the active resolver.

$ cat /etc/resolv.conf
$ resolvectl status | head -60 # systemd-resolved
$ dig @1.1.1.1 google.com # query a specific DNS server

Capturing Traffic (when you’re stuck)

When symptoms don’t match what you expect, capture packets. This confirms whether packets leave/arrive and what DNS/IP is actually used.

$ sudo tcpdump -i eth0 -nn port 53
$ sudo tcpdump -i any -nn host 8.8.8.8

Configuration Files

/etc/hosts - Local DNS entries
/etc/resolv.conf - DNS servers
/etc/netplan/*.yaml - Ubuntu network config
/etc/sysconfig/network-scripts/ - RHEL network config

Example: Netplan (Ubuntu)

Netplan config is YAML and typically applied via netplan apply. Example for a static IP:

# /etc/netplan/01-netcfg.yaml
network:
version: 2
ethernets:
eth0:
dhcp4: no
addresses: [\"192.0.2.10/24\"]
gateway4: \"192.0.2.1\"
nameservers:
addresses: [\"1.1.1.1\", \"8.8.8.8\"]

$ sudo netplan try
$ sudo netplan apply

✅ Practice (15–20 minutes)

Run ip addr and ip route, then explain how your machine reaches the internet.
Use dig to query DNS directly (try different resolvers like 1.1.1.1 and 8.8.8.8).
Check open ports with ss -tulpn and map each to a service/process.