Intro

Updated

September 4, 2026

Intro

Configure and diagnose connectivity: addresses and routes (ip), sockets (ss), DNS, HTTP clients, SSH/file transfer, firewalls, and packet capture. Prefer modern tools (ip/ss/nft) over legacy ones.

Commands in this part

Command Role
ip ip (from iproute2) configures and displays interfaces, addresses, routes, neighbors, rules, and tunnels.
ss ss (socket statistics) inspects TCP/UDP/UNIX sockets.
ping ping sends ICMP Echo Request packets and reports whether a host answers with Echo Reply, plus round-trip time (RTT).
traceroute traceroute maps the path packets take toward a destination by sending probes with increasing TTL and reading ICMP…
mtr mtr (My Traceroute) combines continuous ping and traceroute: it probes each hop on the path and updates loss and…
dig dig (Domain Information Groper) queries DNS servers and prints detailed answers.
host host is a simple DNS lookup utility from BIND tools.
nslookup nslookup queries DNS name servers interactively or non-interactively.
doggo doggo is a modern command-line DNS client with colorful, human-friendly output.
resolvectl resolvectl manages and queries systemd-resolved: DNS servers, search/route domains, LLMNR/mDNS, DNSSEC/DoT status,…
curl curl transfers data to/from URLs.
wget wget is a non-interactive downloader for HTTP(S), FTP, and related protocols.
ssh ssh (OpenSSH client) creates encrypted sessions to a remote host for shell access, command execution, port…
scp scp (secure copy) copies files to or from a remote host over SSH.
rsync rsync synchronizes files and directories locally or over a remote shell (almost always SSH).
nc nc (netcat) is a Swiss-army TCP/UDP tool: open connections, listen for inbound sockets, scan ports simply, and pipe…
tcpdump tcpdump captures and displays packets on a network interface.
nmap The nmap (Network Mapper) is a powerful open-source tool for network exploration, security scanning, and auditing.
openssl openssl is a Swiss-army toolkit for TLS/SSL, X.509 certificates, keys, digests, and simple encrypted files.
nmcli nmcli is the CLI for NetworkManager.
ufw ufw (Uncomplicated Firewall) is Ubuntu’s friendly frontend to netfilter.
nft nft is the userspace CLI for nftables, the modern Linux packet-filtering framework that replaces legacy iptables…
iptables iptables configures IPv4 packet filtering/NAT via netfilter.
ifconfig ifconfig configures and displays network interfaces from the legacy net-tools package.
netstat netstat displays network connections, listening sockets, routing tables, and interface statistics from the legacy…
ftp ftp is the classic interactive client for the File Transfer Protocol.
telnet telnet is a historic remote terminal protocol client.
ssh-keygen ssh-keygen creates and manages SSH key pairs, fingerprints host keys, and can update known_hosts.
ssh-copy-id ssh-copy-id installs your public key on a remote account’s ~/.ssh/authorized_keys with safer permissions than…
sftp sftp is the interactive SSH file-transfer client (SFTP subsystem).
ethtool ethtool queries and controls Ethernet NIC settings: link speed/duplex, offloads, ring parameters, and driver info.
firewall-cmd firewall-cmd is the client for firewalld, the dynamic firewall manager on Fedora, RHEL, CentOS Stream, and many…

Suggested starting points

  1. Local stack: ip, ss, nmcli/resolvectl as appropriate.
  2. Path checks: ping, traceroute/mtr, then dig/host for DNS.
  3. HTTP and APIs: curl (and wget for simple downloads).
  4. Remote admin: ssh, keys via ssh-keygen/ssh-copy-id, files via scp/sftp/rsync.
  5. Firewalls: ufw (Ubuntu), firewall-cmd (firewalld), or nft/iptables.
  6. Deep debug: tcpdump, nmap, openssl, ethtool.