The field card

Everything on this page is something you will type or tap while standing in a venue with somebody waiting. Learn the six commands in the first table by heart. Look the rest up.

One rule before any of it. Run the command, then read what it actually says, then decide. Most wasted time in a machine room is somebody running the right command and not reading the output.

Block 1: The six commands#

On macOS ifconfig still works and Linux has largely moved to ip addr. Learn ifconfig first, because it is the one that exists on the machine you are standing at.

Block 2: What each one is actually telling you#

ipconfig /all and ifconfig#

The first thing you run, every time, before forming any opinion.

Read four lines and only four:

Windows          ipconfig /all
                 ipconfig /release   then   ipconfig /renew     ask again for DHCP
                 ipconfig /flushdns                             clear cached names

macOS            ifconfig en0
                 ipconfig getifaddr en0                         just the address
                 sudo ipconfig set en0 DHCP                     ask again for DHCP

Linux            ip addr show
                 ip route show                                  the gateway

169.254.x.x is the single most useful thing on this page. It is APIPA, the address a machine gives itself when it asked for DHCP and got silence. It means: no DHCP server, or no link, or the wrong VLAN. It never means the machine is broken.

ping#

Asks "are you there" at layer 3. Four outcomes, and each one means something different:

Useful flags: ping -t on Windows and ping on macOS run until you stop them, which is how you watch a link while somebody wiggles a cable. ping -s 1472 sends a large packet, which finds MTU problems that a small ping walks straight past.

Ping proves reachability, not correctness. A node that pings and does not output is a normal Tuesday: the address is right and something above layer 3 is wrong.

tracert and traceroute#

Shows every router between you and the target. On a flat show network the answer is usually one hop, and that is the useful part: if a trace on a show network shows several hops, somebody has routed traffic that should have been local.

Where it earns its keep is the venue network: it tells you exactly which box stops answering, so you know whose problem it is before the conversation starts.

arp -a#

Layer 2. A list of the IP addresses this machine has recently talked to and the MAC address behind each one. Two things it finds that nothing else does:

• The duplicate IP. Two devices on one address, and the ARP table flips between two MACs. Nothing else diagnoses this so quickly.
• The device with an address you did not expect, which is the touring node still set to last venue's scheme.

netstat -an#

What is listening, and what is connected. On a show machine the useful question is narrow:

Windows     netstat -ano | findstr :6454        who has the Art-Net port?
macOS       sudo lsof -i :6454
            sudo lsof -i UDP:5568               sACN

If two applications both want a port, the second one loses, silently. This is why two lighting applications on one laptop is a bad idea, and this is the command that proves it.

The rest, when you need them#

Windows     getmac                              MAC addresses only
            route print                         the routing table
            ipconfig /displaydns
            Test-NetConnection host -Port 6454  PowerShell, tests a port not just a host

macOS       networksetup -listallhardwareports  which interface is which
            netstat -rn                         routing table
            nc -vz host 6454                    tests a single port
            arp -a -d                           clear the ARP cache

Block 3: Setting an address, on everything you will meet#

When to use static. Every show device that another device has to find by address gets a static IP: consoles, nodes, media servers, processors. DHCP is for laptops, phones and anything that only needs to reach the internet. A show that depends on a DHCP server is a show with an extra thing to fail at 19:45.

Write it down before you type it. The IP schedule is a document, not a memory.

Windows 11 and 10#

Settings → Network & internet → Ethernet → IP assignment → Edit → Manual → IPv4 on. Enter the address, the mask (or the prefix length, /24), and leave the gateway blank if there is no route off this network.

Faster, and the one to learn:

ncpa.cpl                                        opens the adapter list directly

Then right click the adapter → Properties → Internet Protocol Version 4 → Properties.

The Windows trap that costs the most time. Windows labels each network Public or Private, and the firewall behaves completely differently between them. On Public it blocks most inbound traffic, which means your media server can reach the console and the console cannot reach it. A network you have just plugged into is Public by default.

Settings → Network & internet → Ethernet → Network profile type → Private. Do this before diagnosing anything else, because the symptom is "it works one way", and that symptom sends people looking at the switch for an hour.

macOS#

System Settings → Network → the interface → Details → TCP/IP → Configure IPv4: Manually.

macOS has one feature worth knowing: Locations. Network → the three dots menu → Locations → Edit Locations. Make one called SHOW with your static addresses and one called HOME with DHCP, and switch between them in two clicks rather than retyping.

networksetup -listallnetworkservices
networksetup -setmanual "Ethernet" 192.168.1.20 255.255.255.0
networksetup -setdhcp "Ethernet"

macOS will also happily hold several addresses on one interface, which is how you talk to a device on 2.x.x.x and one on 192.168.x.x without re-patching. Add a second configuration under the same interface.

iOS and iPadOS#

Settings → Wi-Fi → the ⓘ next to the network → Configure IP → Manual.

You get IP address, subnet mask, router. There is no static option for cellular, and there is no Ethernet screen unless a USB adapter is attached, in which case it appears as its own entry under Settings → Ethernet.

What this is for. A focus tablet, a remote for a desk, a monitoring page. Note that iOS will drop a Wi-Fi network with no internet access unless you tell it not to, and that "no internet" is the normal state of a show network.

Android#

Settings → Network & internet → Internet → the gear next to the network → Advanced → IP settings → Static.

The wording moves between manufacturers. Samsung puts it under the network name after a long press. The fields are the same everywhere: IP address, gateway, prefix length (type 24, not 255.255.255.0), DNS.

The Android trap. Many builds require a gateway and a DNS entry even when there is no route off the network. Put the switch's address, or the device's own address, in both. It does not have to be reachable, it has to be filled in.

Block 4: What to type when#

Every line in that table is somewhere in the diagnostic ladder from Class 3. The commands do not replace the ladder, they are how you climb one rung of it and get an answer instead of an impression.