Exhaust a subnet and prove existing hosts are unaffected

applied · 70 min · Objective 6.4

Task

Address exhaustion has an unmistakable signature: everything running is fine and nothing new can start. Produce it deliberately on a small network, then work through the arithmetic of why subnets fill faster than people expect.

Steps

  1. Create a local network with a very small range -- a /29 or /28. Calculate the usable addresses AFTER the reserved ones and record the arithmetic in lab/net/exhaust.md.
  2. Start containers until creation fails. Record how many you got, compare it against your calculation, and record the exact error.
  3. While in the exhausted state, confirm the EXISTING containers are completely healthy: they serve traffic, they reach each other, nothing about them is degraded. Record this evidence explicitly.
  4. Add a second interface to one existing container and record whether that consumes an address too -- because addresses are consumed per interface, not per workload.
  5. Attempt to expand the network's range in place, record whether the tool allows it, and write what the cloud equivalent means for the range-sizing decision made back in objective 1.3.

Verify

grep -Ec '[0-9]+ usable|[0-9]+ address' lab/net/exhaust.md
grep -Eci 'existing .*(healthy|fine|unaffected)' lab/net/exhaust.md
grep -Eci 'interface' lab/net/exhaust.md
grep -Eci 'expand|resize|cannot' lab/net/exhaust.md

All four non-zero. The evidence that existing workloads are healthy is the signature: any fault where running things are fine and new things cannot start should send you straight to address capacity.

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