Ethernet

What this topic solves

IEEE 802.3 framing, MAC addressing, FCS, MTU, duplex, autonegotiation, copper, fiber and PHY behavior.

Follow state and packet path

Relate encapsulation, addressing, state and packet path. Separate data, control and management planes before troubleshooting.

Input → classification/state → decision → table → next-hop/output → counters

Design before configuration

• Define the failure domain and expected convergence behavior.
• Document addressing, identifiers, timers, MTU and policy boundaries.
• Prefer explicit, observable state over assumptions.
• Plan rollback and out-of-band access before risky changes.

Commands and verification

Command syntax varies by platform and software release. The examples below come from the existing portal content and must be validated against the target platform documentation before production use.

Preamble | SFD | Destination MAC | Source MAC | Type/Length | Payload | FCS
   7 B      1 B        6 B              6 B          2 B       ...     4 B

Aplicação
  ↓
TCP/UDP
  ↓
IP packet  ← MTU precisa acomodar este pacote no enlace
  ↓
Ethernet + tags/encapsulamentos
  ↓
PHY

Evidence-driven workflow

1. Define source, destination, time window and exact symptom.
2. Establish the expected healthy state and compare it with the observed state.
3. Inspect counters, tables, logs and packet captures before resets.
4. Test one hypothesis at a time and prefer reversible changes.
5. Repeat the original test after correction and check side effects.

IEEE 802.3

Use the current standard/RFC and the documentation for the exact software release being operated. Vendor syntax is an implementation detail; protocol behavior should be understood independently.

Prove the behavior in a controlled topology

Build the smallest topology that reproduces the mechanism, capture control and data traffic, introduce one deliberate failure and diagnose it before applying the fix.

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