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Module 5
Ethernet Switching Fundamentals
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# 📘 CCNA 200-301 - Video 5: Ethernet Switching Fundamentals ## Deep Study Notes --- ## 📌 Learning Objectives By the end of this video, you should understand: - What Ethernet is and how it works - MAC addresses structure and purpose - How switches learn MAC addresses - How switches forward frames (CAM table) - Collision domains vs. broadcast domains - Switch forwarding methods - Frame switching process --- ## 🧠 Core Concepts ### 1. What is Ethernet? **Definition:** Ethernet is the most widely used Local Area Network (LAN) technology. It defines the physical and data link layer specifications for wired networks (IEEE 802.3 standards). **Analogy:** Think of Ethernet like a postal system within a city. Each house (device) has a unique address (MAC address). The postal worker (switch) learns where each house is located and delivers packages (frames) directly to the correct address without disturbing other houses. **Ethernet History:** | Year | Development | |------|-------------| | 1973 | Invented by Robert Metcalfe at Xerox PARC | | 1980 | DIX standard (Digital, Intel, Xerox) | | 1983 | IEEE 802.3 standard published | | 1995 | Fast Ethernet (100 Mbps) | | 1999 | Gigabit Ethernet (1000 Mbps) | | 2002 | 10 Gigabit Ethernet | | Today | 400 Gigabit Ethernet available | --- ### 2. MAC Addresses (Media Access Control) **Definition:** A MAC address is a unique 48-bit (6-byte) hardware address burned into the Network Interface Card (NIC) by the manufacturer. **Format:** ``` MAC Address: 00:1A:2B:3C:4D:5E └──────┬──────┘ └───┬───┘ OUI Device ID (Organizationally (Unique to Unique Identifier) each NIC) Binary Representation: 00000000 00011010 00101011 00111100 01001101 01011110 ``` **MAC Address Structure:** | Field | Size | Description | |-------|------|-------------| | **OUI** | 24 bits (3 bytes) | Assigned to manufacturer by IEEE | | **Device ID** | 24 bits (3 bytes) | Unique serial number from manufacturer | **Special MAC Address Types:** | Type | Format | Example | Purpose | |------|--------|---------|---------| | **Unicast** | First byte LSB = 0 | 00:1A:2B:3C:4D:5E | Single specific device | | **Multicast** | First byte LSB = 1 | 01:00:5E:00:00:01 | Group of devices | | **Broadcast** | All bits = 1 | FF:FF:FF:FF:FF:FF | All devices on segment | **MAC Address Flags (First Byte LSB bits):** ``` Byte 1: 00:1A:2B... │││││││└─ Individual/Group (0=Unicast, 1=Multicast) ││││││└── Globally Unique/Local Administered └┴┴┴┴┴─── OUI bits ``` **Key Facts:** - MAC addresses are **48 bits** (6 bytes / 12 hexadecimal characters) - Every NIC has a **unique** MAC address - MAC addresses are **layer 2** addresses - They operate within a **local network** (not routable) - Also called: **Burned-in Address (BIA)**, hardware address, physical address --- ### 3. Switch Fundamentals **What is a Switch?** A switch is a Layer 2 device that connects multiple devices within the same network and forwards frames based on MAC addresses. **Switch vs. Hub:** | Feature | Hub (Layer 1) | Switch (Layer 2) | |---------|---------------|------------------| | **Forwarding** | Floods to all ports | Forwards only to destination port | | **Collisions** | Single collision domain | Per-port collision domain | | **Bandwidth** | Shared | Dedicated per port | | **Intelligence** | None (repeater) | Learns MAC addresses | | **Security** | All devices see all traffic | Traffic isolated to destination | | **Performance** | Degrades with more devices | Consistent performance | **Visual Comparison:** ``` HUB (Shared Bandwidth) SWITCH (Dedicated Bandwidth) ┌─────────────────┐ ┌─────────────────────────┐ │ HUB │ │ SWITCH │ │ ┌───┐ ┌───┐ │ │ ┌───┐ ┌───┐ ┌───┐ │ │ │PC1│ │PC2│ │ │ │PC1│ │PC2│ │PC3│ │ │ └─┬─┘ └─┬─┘ │ │ └─┬─┘ └─┬─┘ └─┬─┘ │ │ │ │ │ │ │ │ │ │ │ ┌─┴─────┴─┐ │ │ ┌─┴─────┴─────┴─┐ │ │ │ All │ │ │ │ Independent │ │ │ │ Traffic │ │ │ │ Paths │ │ │ │ Collides│ │ │ └────────────────┘ │ │ └─────────┘ │ │ │ └─────────────────┘ └─────────────────────────┘ 100 Mbps shared 100 Mbps per port = 33 Mbps each when 3 active = 100 Mbps each ``` --- ### 4. CAM Table (Content Addressable Memory) **Definition:** A CAM table (also called MAC address table or bridging table) is the database that a switch uses to learn and store MAC addresses and their associated ports. **CAM Table Structure:** ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ SWITCH CAM TABLE │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ MAC Address │ Port │ VLAN │ Age (seconds) │ │ ├─────────────────────┼────────────┼────────────┼─────────────────────────┤ │ │ 00:1A:2B:3C:4D:5E │ Fa0/1 │ 1 │ 120 │ │ │ 00:1A:2B:3C:4D:5F │ Fa0/2 │ 1 │ 45 │ │ │ 00:1A:2B:3C:4D:60 │ Fa0/3 │ 1 │ 300 │ │ │ 00:1A:2B:3C:4D:61 │ Fa0/4 │ 1 │ 10 │ │ └─────────────────────┴────────────┴────────────┴─────────────────────────┘ ``` **How the Switch Learns MAC Addresses:** ``` Step 1: Frame arrives on a port ┌─────────┐ │ PC1 │ │ MAC: AA │ └────┬────┘ │ Frame: Src=AA, Dst=BB ▼ ┌─────────┐ │ SWITCH │ └─────────┘ Step 2: Switch examines Source MAC - Learns: MAC AA is on Port 1 - Adds to CAM table Step 3: Switch examines Destination MAC - If known: forward to specific port - If unknown: flood to all ports (except source) Step 4: Aging timer (default 300 seconds) - Entries removed if no traffic received - Prevents stale entries ``` --- ### 5. Frame Forwarding Process **Three Possible Actions:** ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ SWITCH FORWARDING DECISIONS │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ 1. UNKNOWN UNICAST (Destination not in CAM) │ │ ┌─────────────────────────────────────────────────────────────────┐ │ │ │ Frame arrives → Destination MAC not in table → FLOOD to all │ │ │ │ ports except source port │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ │ 2. KNOWN UNICAST (Destination in CAM) │ │ ┌─────────────────────────────────────────────────────────────────┐ │ │ │ Frame arrives → Destination MAC found → FORWARD to specific │ │ │ │ port only │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ │ 3. BROADCAST/MULTICAST │ │ ┌─────────────────────────────────────────────────────────────────┐ │ │ │ Frame arrives → Destination is broadcast (FF:FF:FF:FF:FF:FF) │ │ │ │ or multicast → FLOOD to all ports except source port │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` **Frame Forwarding Example:** ``` Scenario: PC1 (MAC AA) wants to send to PC3 (MAC CC) ┌─────┐ ┌─────┐ ┌─────┐ │ PC1 │ │ PC2 │ │ PC3 │ │ AA │ │ BB │ │ CC │ └──┬──┘ └──┬──┘ └──┬──┘ │ │ │ └──────────────┼──────────────┘ ┌─────▼─────┐ │ SWITCH │ │ CAM Table │ │ AA → Port1│ │ BB → Port2│ └───────────┘ Step 1: PC1 sends frame to PC3 (Src: AA, Dst: CC) Step 2: Switch receives on Port1 Step 3: Switch learns: AA is on Port1 (updates/refreshes) Step 4: Switch looks up CC in CAM table - CC NOT in table → UNKNOWN Step 5: Switch floods frame to Port2 and Port3 Step 6: PC2 receives (not for it) → discards Step 7: PC3 receives (for it) → processes Step 8: PC3 replies to PC1 → Switch learns CC on Port3 ``` --- ### 6. Collision Domains vs. Broadcast Domains **Collision Domain:** - Segment where two or more devices share the same medium - Collisions occur when multiple devices transmit simultaneously - Switches **break** collision domains (each port = separate domain) **Broadcast Domain:** - Segment where broadcast frames are received by all devices - Switches **do NOT break** broadcast domains (by default) - Routers **break** broadcast domains ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ COLLISION vs. BROADCAST DOMAINS │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ HUB NETWORK: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ BROADCAST DOMAIN │ │ │ │ ┌────────────────────────────────────────────────────────────────┐ │ │ │ │ │ COLLISION DOMAIN (One) │ │ │ │ │ │ │ │ │ │ │ │ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ │ │ │ │ │ │ │ PC1 │ │ PC2 │ │ PC3 │ │ HUB │ │ │ │ │ │ │ └─────┘ └─────┘ └─────┘ └─────┘ │ │ │ │ │ └────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ SWITCH NETWORK: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ BROADCAST DOMAIN │ │ │ │ │ │ │ │ ┌─────────┐ ┌─────────┐ ┌─────────┐ ┌─────────┐ │ │ │ │ │ CD 1 │ │ CD 2 │ │ CD 3 │ │ CD 4 │ │ │ │ │ │ ┌─────┐ │ │ ┌─────┐ │ │ ┌─────┐ │ │ ┌─────┐ │ │ │ │ │ │ │ PC1 │ │ │ │ PC2 │ │ │ │ PC3 │ │ │ │SWITCH│ │ │ │ │ │ └─────┘ │ │ └─────┘ │ │ └─────┘ │ │ └─────┘ │ │ │ │ │ └─────────┘ └─────────┘ └─────────┘ └─────────┘ │ │ │ │ │ │ │ │ Each port = separate collision domain │ │ │ │ All ports = same broadcast domain (by default) │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` **Key Numbers:** | Device | Collision Domains | Broadcast Domains | |--------|-------------------|-------------------| | **Hub** | 1 | 1 | | **Switch** | 1 per port | 1 (all ports) | | **Router** | 1 per interface | 1 per interface | **Formula:** - Collision domains = number of switch ports (for switch) - Broadcast domains = number of VLANs or router interfaces --- ### 7. Switch Forwarding Methods **Three Methods:** ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ SWITCH FORWARDING METHODS │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ 1. STORE-AND-FORWARD │ │ ┌─────────────────────────────────────────────────────────────────┐ │ │ │ ┌─────────┐ ┌─────────┐ ┌─────────┐ │ │ │ │ │ Receive │───►│ Store │───►│ Check │───► Forward │ │ │ │ │ Frame │ │ Entire │ │ FCS │ │ │ │ │ └─────────┘ │ Frame │ └─────────┘ │ │ │ │ └─────────┘ │ │ │ │ │ │ │ │ Pros: Lowest error rate, checks integrity │ │ │ │ Cons: Higher latency (stores whole frame) │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ │ 2. CUT-THROUGH │ │ ┌─────────────────────────────────────────────────────────────────┐ │ │ │ ┌─────────┐ ┌─────────────────────────────────────────────┐ │ │ │ │ │ Read │───►│ Forward as soon as destination MAC read │ │ │ │ │ │ MAC │ │ (first 6 bytes) │ │ │ │ │ └─────────┘ └─────────────────────────────────────────────┘ │ │ │ │ │ │ │ │ Pros: Lowest latency │ │ │ │ Cons: Forwards corrupt frames (no FCS check) │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ │ 3. FRAGMENT-FREE (Modified Cut-Through) │ │ ┌─────────────────────────────────────────────────────────────────┐ │ │ │ ┌─────────┐ ┌─────────┐ ┌─────────────────────────────┐ │ │ │ │ │ Read │───►│ Check │───►│ Forward after 64 bytes │ │ │ │ │ │ First │ │ First │ │ (avoids most collisions) │ │ │ │ │ │ 64 bytes│ │ 64 bytes│ │ │ │ │ │ │ └─────────┘ └─────────┘ └─────────────────────────────┘ │ │ │ │ │ │ │ │ Pros: Balance of speed and error detection │ │ │ │ Cons: Still forwards some corrupt frames │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` **Comparison Table:** | Method | Latency | Error Checking | Best For | |--------|---------|----------------|----------| | Store-and-Forward | High | Full (FCS) | Critical data, WAN links | | Cut-Through | Low | None | High-performance networks | | Fragment-Free | Medium | Partial (first 64B) | Mixed traffic | --- ### 8. Ethernet Frame Structure **Ethernet II Frame (Most Common):** ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ ETHERNET II FRAME (DIX) │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ Bytes: 6 6 2 46-1500 4 │ │ ┌─────────────┬─────────────┬───────┬─────────────┬─────────┐ │ │ │ Destination │ Source │ Type │ Data │ FCS │ │ │ │ MAC │ MAC │ │ │ (CRC32) │ │ │ └─────────────┴─────────────┴───────┴─────────────┴─────────┘ │ │ │ │ Minimum Frame Size: 64 bytes │ │ Maximum Frame Size: 1518 bytes (without VLAN tag) │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` **Frame Fields:** | Field | Size | Description | |-------|------|-------------| | **Preamble** | 7 bytes | Synchronization (alternating 1s and 0s) | | **SFD** | 1 byte | Start Frame Delimiter (10101011) | | **Destination MAC** | 6 bytes | Receiver's MAC address | | **Source MAC** | 6 bytes | Sender's MAC address | | **Type/Length** | 2 bytes | Protocol type (0x0800 for IP) or length | | **Data/Payload** | 46-1500 bytes | Upper layer data (minimum 46 bytes) | | **FCS** | 4 bytes | Frame Check Sequence (CRC for error detection) | **Type Field Common Values:** | Value | Protocol | |-------|----------| | 0x0800 | IPv4 | | 0x0806 | ARP | | 0x86DD | IPv6 | | 0x8100 | 802.1Q VLAN Tag | --- ### 9. Switch Port Operations **Port States:** ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ SWITCH PORT STATES (STP) │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ DISABLED │ │ │ │ │ ▼ │ │ BLOCKING ─────────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ (20 sec max age) │ │ │ ▼ │ │ │ LISTENING ────────────────────────────────────────────────────────────┤ │ │ │ │ │ │ │ (15 sec forward delay) │ │ │ ▼ │ │ │ LEARNING ─────────────────────────────────────────────────────────────┤ │ │ │ │ │ │ │ (15 sec forward delay) │ │ │ ▼ │ │ │ FORWARDING ───────────────────────────────────────────────────────────┘ │ │ │ │ Note: Without STP, ports typically go directly to FORWARDING │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` **Port Types:** | Port Type | Description | |-----------|-------------| | **Access Port** | Carries traffic for single VLAN (connects to end devices) | | **Trunk Port** | Carries traffic for multiple VLANs (connects to other switches) | --- ## 🔧 Commands ### Switch Verification Commands ```cisco ! View MAC address table (CAM table) Switch> enable Switch# show mac address-table Switch# show mac address-table dynamic Switch# show mac address-table static ! Example output: ! Mac Address Table ! ------------------------------------------- ! Vlan Mac Address Type Ports ! ---- ----------- -------- ----- ! 1 00:1a:2b:3c:4d:5e DYNAMIC Fa0/1 ! 1 00:1a:2b:3c:4d:5f DYNAMIC Fa0/2 ! 1 00:1a:2b:3c:4d:60 DYNAMIC Fa0/3 ! Clear MAC address table Switch# clear mac address-table dynamic ! View aging time Switch# show mac address-table aging-time ! Set aging time (global config) Switch(config)# mac address-table aging-time 300 ! Add static MAC entry Switch(config)# mac address-table static 00:1a:2b:3c:4d:5e vlan 1 interface fastEthernet 0/1 ! View interface status Switch# show interfaces status Switch# show interfaces fastEthernet 0/1 ! View switch port security Switch# show port-security Switch# show port-security interface fastEthernet 0/1 ``` ### Switch vs. Router Commands (Future Reference) ```cisco ! Router: views networks beyond local Router# show ip route ! Switch: views local MAC addresses Switch# show mac address-table ``` --- ## 📊 Text-Based Diagrams ### Switch Learning Process Flow ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ SWITCH MAC LEARNING FLOW │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ START │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Frame received on port X │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Extract Source MAC address │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Is Source MAC in CAM table? │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ │ ├─────────YES────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ ┌─────────────────────────────────────────────────────────────┐ │ │ │ │ │ Update age timer │ │ │ │ │ └─────────────────────────────────────────────────────────────┘ │ │ │ │ │ │ │ └─────────NO────────────────────────────────────────────────────────┘ │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Add entry: MAC address → Port X │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Extract Destination MAC address │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Is Destination MAC in CAM table? │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ │ ├─────────YES────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ ┌─────────────────────────────────────────────────────────────┐ │ │ │ │ │ Forward frame to specific port Y │ │ │ │ │ └─────────────────────────────────────────────────────────────┘ │ │ │ │ │ │ │ └─────────NO────────────────────────────────────────────────────────┘ │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Flood frame to all ports except source port │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` ### Collision vs. Broadcast Domain Visual ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ EXAMPLE: 24-PORT SWITCH + 1 ROUTER │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ ┌─────────┐ │ │ │ Router │ │ │ │ R1 │ │ │ └────┬────┘ │ │ │ │ │ ┌──────────────────────┼──────────────────────────────────────────────┐ │ │ │ │ │ │ │ │ ┌───────────────────▼───────────────────┐ │ │ │ │ │ SWITCH (L2) │ │ │ │ │ │ │ │ │ │ │ │ Port1 Port2 Port3 ... Port24 │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ ▼ ▼ ▼ ▼ │ │ │ │ │ │ ┌───┐ ┌───┐ ┌───┐ ┌───┐ │ │ │ │ │ │ │PC1│ │PC2│ │PC3│ ... │PC24│ │ │ │ │ │ │ └───┘ └───┘ └───┘ └───┘ │ │ │ │ │ │ │ │ │ │ │ │ BROADCAST DOMAINS: │ │ │ │ │ │ ┌─────────────────────────────────┐ │ │ │ │ │ │ │ All 24 ports = 1 broadcast │ │ │ │ │ │ │ │ domain (unless VLANs) │ │ │ │ │ │ │ └─────────────────────────────────┘ │ │ │ │ │ │ │ │ │ │ │ │ COLLISION DOMAINS: │ │ │ │ │ │ ┌─────────────────────────────────┐ │ │ │ │ │ │ │ 24 separate collision domains │ │ │ │ │ │ │ │ (1 per port) │ │ │ │ │ │ │ └─────────────────────────────────┘ │ │ │ │ │ └───────────────────────────────────────┘ │ │ │ │ │ │ │ └──────────────────────────────────────────────────────────────────────┘ │ │ │ │ Router adds: │ │ - Additional broadcast domain on its other interfaces │ │ - Each router interface = separate broadcast domain │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ## ✅ Exam Tips (For CCNA 200-301) | Topic | What Cisco Tests | |-------|------------------| | **MAC Address** | 48-bit, OUI, unicast vs. multicast, broadcast FF:FF:FF:FF:FF:FF | | **Switch Learning** | How switches build CAM tables | | **Flooding** | When switches flood (unknown unicast, broadcast) | | **Collision Domains** | Hubs = 1, Switches = 1 per port | | **Broadcast Domains** | Switches don't break by default, routers do | | **Frame Forwarding** | Store-and-forward vs. cut-through | ### Common Exam Scenarios: **Scenario 1:** "A switch receives a frame with a destination MAC address not in its CAM table. What does it do?" - **Answer:** Floods the frame out all ports except the receiving port **Scenario 2:** "How many collision domains are created by an 8-port switch?" - **Answer:** 8 collision domains (one per port) **Scenario 3:** "What is the purpose of the FCS field in an Ethernet frame?" - **Answer:** Error detection (CRC check) ### Mnemonics: **Ethernet Frame Fields (Preamble to FCS):** **"Please Send Data To Frank's Computer"** - **P**reamble - **S**FD - **D**estination MAC - **T**ype/Length - **F**CS (Frame Check Sequence) **Switch Forwarding Decisions:** **"Unknown = Flood, Known = Forward, Broadcast = Flood"** --- ## 📝 Summary (1-Minute Revision) ``` SWITCHING FUNDAMENTALS: MAC ADDRESS: ├── 48 bits (6 bytes) ├── Format: XX:XX:XX:XX:XX:XX ├── OUI (first 24 bits) = manufacturer ├── Unicast: individual device ├── Broadcast: FF:FF:FF:FF:FF:FF └── Multicast: first byte LSB = 1 SWITCH OPERATION: ├── Learns MAC addresses from source ├── Stores in CAM table (MAC → Port) ├── Forwards based on destination MAC ├── Unknown unicast = FLOOD ├── Broadcast = FLOOD └── Known unicast = FORWARD TO SPECIFIC PORT COLLISION DOMAINS: ├── Hub: 1 domain ├── Switch: 1 per port └── Switch breaks collision domains BROADCAST DOMAINS: ├── Switch: 1 domain (all ports) ├── Router: breaks domains └── VLAN: breaks domains FORWARDING METHODS: ├── Store-and-Forward: full check, higher latency ├── Cut-Through: low latency, no error check └── Fragment-Free: checks first 64 bytes CAM TABLE: └── show mac address-table ``` --- ## 🧪 Practice Questions **1. How many bytes are in a MAC address?** - A) 4 bytes - B) 6 bytes - C) 8 bytes - D) 12 bytes <details> <summary>Answer</summary> <b>B) 6 bytes (48 bits)</b> - MAC addresses are 48-bit addresses expressed as 12 hexadecimal characters. </details> **2. What does a switch do when it receives a frame with a destination MAC address not in its CAM table?** - A) Drops the frame - B) Sends the frame back to the source - C) Floods the frame out all ports except the receiving port - D) Sends an ARP request <details> <summary>Answer</summary> <b>C) Floods the frame out all ports except the receiving port</b> - This is called flooding and allows the switch to learn the location of the destination device. </details> **3. How many collision domains are created by a 24-port switch?** - A) 1 - B) 12 - C) 24 - D) 48 <details> <summary>Answer</summary> <b>C) 24</b> - Each switch port creates its own collision domain. </details> **4. Which switching method stores the entire frame and verifies the FCS before forwarding?** - A) Cut-through - B) Fragment-free - C) Store-and-forward - D) Fast-forward <details> <summary>Answer</summary> <b>C) Store-and-forward</b> - This method stores the entire frame, verifies integrity with FCS, then forwards. </details> **5. What is the broadcast MAC address?** - A) 00:00:00:00:00:00 - B) FF:FF:FF:FF:FF:FF - C) 01:00:5E:00:00:01 - D) 11:11:11:11:11:11 <details> <summary>Answer</summary> <b>B) FF:FF:FF:FF:FF:FF</b> - All bits set to 1 indicates a broadcast frame. </details> **6. Which device breaks broadcast domains by default?** - A) Hub - B) Switch - C) Router - D) Bridge <details> <summary>Answer</summary> <b>C) Router</b> - Routers do not forward broadcasts, thus breaking broadcast domains. Switches forward broadcasts within a VLAN. </details> **7. What information does a switch use to build its CAM table?** - A) Destination IP address - B) Source IP address - C) Destination MAC address - D) Source MAC address <details> <summary>Answer</summary> <b>D) Source MAC address</b> - Switches learn by examining the source MAC address of incoming frames. </details> **8. What is the minimum size of an Ethernet frame (excluding preamble)?** - A) 46 bytes - B) 64 bytes - C) 1500 bytes - D) 1518 bytes <details> <summary>Answer</summary> <b>B) 64 bytes</b> - The minimum Ethernet frame size is 64 bytes (including destination, source, type, data, FCS). Minimum payload is 46 bytes. </details> **9. A switch receives a frame with destination MAC address of 01:00:5E:00:00:01. How does it forward this frame?** - A) To a single specific port - B) To all ports (flood) - C) Only to ports with devices subscribed to that multicast group - D) Discards the frame <details> <summary>Answer</summary> <b>C) Only to ports with devices subscribed to that multicast group</b> - With IGMP snooping enabled, switches forward multicast only to interested ports. </details> **10. What command displays the MAC address table on a Cisco switch?** - A) `show mac-address` - B) `show mac address-table` - C) `show cam table` - D) `show arp` <details> <summary>Answer</summary> <b>B) `show mac address-table`</b> - This is the correct command to view the CAM table on modern Cisco switches. </details> --- ## 📌 Next Steps After completing Video 5, you should be ready for: - **Video 6:** VLANs and Trunking - **Video 7:** Spanning Tree Protocol (STP) **Lab Practice:** Build a network with multiple switches and observe: 1. How switches learn MAC addresses 2. Flooding behavior with unknown unicast 3. Broadcast propagation 4. Using `show mac address-table` to verify learning --- **Ready for Video 6?** Share the link or say "next" and I'll continue with VLANs and Trunking. I'll create comprehensive deep notes for **Video 6: VLANs and Trunking** based on the standard CCNA 200-301 curriculum. ---