showstack

What is my address?

IPv4 address, subnet mask, default gateway. A 169.254 address means DHCP failed and the machine named itself.

IPv4 address	Who this machine is.	169.254.x.x means nobody answered the DHCP request.
Subnet mask	How much of that address is the network.	A mask that disagrees with the other device is the fault.
Default gateway	Where anything non-local is sent.	Blank is normal on a show network, and fine.
Physical address	The MAC — the hardware identity.	This is the number the switch actually learns.

Four lines, and only four. Everything else in that output is noise while you are standing up.

Can I reach that device?

Replies with a time. "Destination host unreachable" is your machine giving up locally; a timeout means it left and nothing came back — different faults.

Replies, times low and steady	It is there and the path is healthy.
Replies, times all over the place	The path is congested.	That is jitter, measured. Write the number down.
Request timed out	It did not answer.	It may still be there and firewalled. Not proof of absence.
Destination host unreachable	Your own machine does not know how to get there.	Check your mask before you touch anything else.

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.

Where does the traffic actually go?

Each hop with its time. A hop that suddenly jumps by tens of milliseconds is the one to ask about. Stars mean that hop declined to answer, not that it is broken.

One hop	Normal on a flat show network.
Several hops	Something that should be local is being routed.	Somebody has put a router in the path. That is the finding.
Stars, then it continues	That hop declined to answer.	Not a fault. Plenty of devices refuse to reply and forward perfectly.
Stars, and it stops	That is where it dies.	Now you know whose problem it is before the conversation starts.

What is on this network?

Every address this machine has spoken to recently, with its MAC. The first three MAC pairs identify the manufacturer, which is often enough to name an unlabelled box.

Two IPs, one MAC	One device answering to two addresses.
One IP, changing MAC	Two devices claiming the same address.	The classic: intermittent, both affected, either works alone.
Nothing at all	You have not talked to anything yet.	The table only lists what this machine has recently spoken to.

This is layer 2, and it finds the duplicate-address fault that nothing at layer 3 can name.

Which way out is it using?

The default route. Two default routes — a wired show network and wifi — is the classic reason traffic vanishes into the wrong interface.

What is listening on this machine?

Local address and port. 0.0.0.0 means every interface; 127.0.0.1 means loopback only, so nothing else can reach it however good the cable is.

Is that port open on the far end?

Succeeded or refused. Refused means something answered and said no; a timeout means nothing answered at all, which usually means a firewall rather than a closed port.

What multicast groups has this machine joined?

sACN groups look like 239.255.x.x. If a receiver has not joined the group, no amount of correct sending will reach it.

Is the name resolving?

The address it resolved to. On a show network with no DNS this is expected to fail — use the address.

How much can this link carry?

Bitrate and retransmits. Retransmits on a supposedly quiet gigabit link mean a duplex mismatch or a failing cable, and they will ruin audio long before they ruin a file copy.

What is actually on the wire?

The packets themselves. Filter to the port you care about first — an unfiltered capture on a show network is unreadable within seconds.