The Wire, 1969
Everything since the first ARPANET link in 1969 is plumbing: addresses, names, routes, ports. This era hands you a Linux host and has you read and repair every layer of it from the command line, from ip a to a packet capture.
Networking track · 31 missions · boss mission, written exam and certificate · free, no signup. Everything below runs in the browser terminal on the SERVBG home page.
What you will do
- show this machine's hostname
hostnameARPANET's first host-to-host message, Oct 29 1969: UCLA typed "LOGIN" to SRI. It crashed after "LO." The network was born mid-crash.
- view network interfaces and their assigned IP
ip aIP address vs MAC address: IP (RFC 791, 1981) is logical and routable; MAC is burned into the NIC at the factory (Xerox PARC Ethernet, 1973). One finds the network, the other finds the wire.
- the old-school way to view interfaces (deprecated)
ifconfigifconfig came from 1980s BSD net-tools. Linux distros defaulted to the newer iproute2 (ip) suite through the 2010s — ifconfig lives on mostly in muscle memory.
- check the static hostname-to-IP map
cat /etc/hosts/etc/hosts predates DNS. Every early ARPANET site once shared a single master HOSTS.TXT file, hand-updated by SRI's Network Information Center and redistributed by FTP.
- see which DNS resolvers this host asks
cat /etc/resolv.confresolv.conf lists nameservers in order. The resolver tries the first, and falls back to the next only after a timeout — a chain of trust, one hop at a time.
- query DNS for the A record
dig servbg.lanPaul Mockapetris designed DNS in 1983 (RFC 882/883) to replace the unscalable single HOSTS.TXT file with a distributed, cached, delegated hierarchy.
- resolve a hostname the older way
nslookup fileserver.servbg.lannslookup predates dig (which shipped with BIND in the 1990s). dig is preferred today, but nslookup is still everywhere, especially on Windows.
- find where email for this domain should be delivered
dig -t MX servbg.lanMX records carry a priority number — lower wins. Multiple MX records give a domain automatic mail-server failover.
- find the authoritative nameservers for a domain
dig -t NS servbg.lanNS records are delegation pointers: root servers point to a TLD, the TLD points to your zone's nameservers. Every DNS lookup walks that chain.
- view the local IP-to-MAC address cache
arp -aARP (RFC 826, 1982) is how IP meets Ethernet: knowing a neighbor's IP is useless until you learn the MAC address to actually address a frame to.
- test reachability to the default gateway
ping 192.168.1.1Mike Muuss wrote ping in 1983, named after sonar. It rides on ICMP Echo Request/Reply (RFC 792) — the network's simplest "are you there?"
- ping an external address and read the loss statistics
ping 8.8.8.8Packet loss is normal on real links — congestion, wireless noise, rate limiting. ping's summary line (packets transmitted/received/% loss) is the first number every network tech checks.
- see what a dead host looks like on the wire
ping 192.168.1.99No ARP reply comes back, so the kernel itself answers "Destination Host Unreachable" — the network layer can't send a frame without a MAC address to put on it.
- see every router hop between you and a destination
traceroute 8.8.8.8Van Jacobson's traceroute (1987) is a clever abuse of TTL: send packets with TTL 1, 2, 3... each expiring router replies "time exceeded," unmasking the whole path one hop at a time.
- read a hop that times out (`* * *`) without panicking
traceroute 192.168.1.20`* * *` means no reply within the timeout — often a device or firewall silently dropping ICMP, not necessarily a broken path. The hops after it still tell the story.
- capture and read raw packets on the wire
tcpdump -i eth0tcpdump (1988, Van Jacobson and Steve McCanne at Lawrence Berkeley Lab) plus libpcap became the direct ancestor of Wireshark.
- list listening TCP and UDP sockets and ports
ss -tulnA port is a 16-bit number defined alongside TCP itself (RFC 793, 1981) — it lets one IP address serve many independent conversations at once. ss reads straight from the kernel and replaced netstat around 2003.
- filter the socket list to UDP only
ss -uTCP (RFC 793, 1981) is reliable and ordered, with a handshake and retransmits. UDP (RFC 768, 1980) is connectionless and best-effort — DNS, DHCP, and live video trade reliability for speed.
- view the routing table with the older tool
netstat -rnThe -n flag matters: it skips reverse-DNS on every address, which is why "numeric" output loads instantly on a struggling network.
- view the routing table with the modern tool
ip rThe default route (0.0.0.0/0) is the internet's fallback rule: "if nothing more specific matches, send it here." Everything off your local subnet leaves through it.
- fetch only the HTTP response headers
curl -I http://fileserver.servbg.lanDaniel Stenberg released curl in 1998. -I sends a HEAD request — the server never sends a body, so you can probe a server cheaply.
- watch the handshake that assigned this host its IP
dhcp renewDHCP (RFC 2131, 1997) is DORA: Discover, Offer, Request, Ack. It replaced the older BOOTP and is why a laptop "just works" on any network it joins.
- check the maximum frame size this link can carry
mtu eth01500 bytes traces back to the 1980 DIX Ethernet II spec. Jumbo frames exist, but 1500 stuck as the internet's lowest common denominator — exceed it and routers must fragment or drop.
- see private addresses translated to a shared public one
natstatNAT (RFC 1631, 1994) was meant as a stopgap. It let IPv4's 4.3 billion addresses outlive the dot-com boom by letting a whole LAN share one public IP.
- state the netmask for a /26 network
255.255.255.192Before CIDR (1993), addressing was rigid class A/B/C blocks. VLSM let one organization carve networks to the exact size needed — no more, no less.
- compute the network address that contains host 192.168.1.130/26
192.168.1.128A /26 gives 4 subnets per /24: .0, .64, .128, .192 — each with 64 addresses, 62 usable. 192.168.1.130 falls in the third block.
- compute the broadcast address for 192.168.1.128/26
192.168.1.191Network address and broadcast address are always the first and last of a block — neither is assignable to a host.
- load the broken-network diagnostic scenario
scenario startGood troubleshooting is a layered method: physical link, then IP config, then routing, then DNS — check each layer before guessing at the next.
- read the routing table to spot the fault
ip rA default route pointing at an address nobody answers for is one of the most common "no internet" tickets in real IT, and one of the fastest to fix once you see it.
- confirm the currently configured gateway is unreachable
ping 192.168.1.254Ping the gateway first, always — it is the cheapest, fastest way to rule an entire class of "no internet" problems in or out.
- Boss missionfix the default route to point at the real gateway
ip route replace default via 192.168.1.1RFC 791 (1981) gave every packet a source and destination address; RFC 793 (1981) gave TCP the handshake that turns those packets into a conversation. Everything in this era sits on that fifty-year-old foundation.
Certificate
This track is certifiable. Clear the boss mission in the terminal, then run EXAM NETWORKING for the written paper: 20 server-graded questions drawn from our own bank, pass mark 14 of 20. The certificate is issued once both are done, and it carries a verification code.
Independently developed; not affiliated with, endorsed by, or sponsored by CompTIA. Content is aligned to CompTIA’s publicly published exam objectives for Network+ (N10-009).