Produce an APIPA address on purpose and read what it tells you

short · 35 min · Objective 2.2

Task

Induce the self-assigned address state deliberately, so that the next time it appears you recognise it as a diagnosis rather than as an unfamiliar number -- and record what it rules in and out.

Steps

  1. On a machine set to obtain an address automatically, disconnect it from any network that offers DHCP -- switch the virtual adapter to an isolated network, or unplug the cable.
  2. Release and renew, wait, then capture the configuration to lab/apipa/state.txt.
  3. Record in lab/apipa/reads.csv with header observation,proves,rules_out at least four things the address proves and at least two it does not.
  4. Record the IPv6 addresses present in lab/apipa/v6.txt and note which are link-local, identifying them by their prefix.
  5. Reconnect, renew, and record the recovered configuration in lab/apipa/recovered.txt.

Verify

grep -Ec '169\.254' lab/apipa/state.txt
awk -F, 'NR>1 && NF>=3 {n++} END {print n" observation(s)"}' lab/apipa/reads.csv
grep -Eic 'fe80' lab/apipa/v6.txt
grep -c . lab/apipa/recovered.txt

An address in the 169.254 range captured, four or more observations recorded, a link-local IPv6 address identified, and a recovered configuration. If the recovered file shows the same 169.254 address, the machine is still isolated -- which is itself the diagnosis this lab is teaching.

Notes

The two-machines-can-see-each-other case is worth trying if you have two virtual machines on the same isolated network: both take APIPA addresses, both can reach each other, and neither can reach anything else.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.