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Module 46
CDP and LLDP
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# 📘 CCNA 200-301 - Video 46: CDP and LLDP ## Deep Study Notes --- ## 📌 Learning Objectives By the end of this video, you should understand: - What CDP (Cisco Discovery Protocol) is and how it works - What LLDP (Link Layer Discovery Protocol) is and how it works - CDP vs. LLDP comparison - CDP configuration and verification - LLDP configuration and verification - Security considerations for discovery protocols --- ## 🧠 Core Concepts ### 1. What is CDP? **Definition:** Cisco Discovery Protocol (CDP) is a Cisco-proprietary Layer 2 protocol that allows network devices to discover neighboring devices and their capabilities, regardless of network layer protocol. **Analogy:** Think of CDP like a neighbor introduction system. Each device periodically announces "Hello, I'm Router A, I'm a Cisco device, and here's what I can do." Neighbors listen and learn about each other. ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ CDP OPERATION │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ CDP Advertisement (Multicast MAC 01:00:0C:CC:CC:CC): │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ Router A Router B │ │ │ │ ┌─────────┐ ┌─────────┐ │ │ │ │ │ │ │ │ │ │ │ │ │ CDP │ "Hello! I'm Router A│ CDP │ │ │ │ │ │ Agent │ Device ID: Router A│ Agent │ │ │ │ │ │ │ Platform: 2911 │ │ │ │ │ │ │ │ Interface: Gi0/0 │ │ │ │ │ │ │ │ IP Address: 10.1.1.1│ │ │ │ │ │ │ │ Capabilities: Router"│ │ │ │ │ │ └─────────┘ ─────────────────────► └─────────┘ │ │ │ │ │ │ │ │ Router A Router B │ │ │ │ ┌─────────┐ ┌─────────┐ │ │ │ │ │ CDP │ │ CDP │ │ │ │ │ │ Agent │ ◄─────────────────────│ Agent │ │ │ │ │ │ │ "Hello! I'm Router B│ │ │ │ │ │ │ │ Device ID: Router B│ │ │ │ │ │ │ │ Platform: 3750 │ │ │ │ │ │ │ │ Interface: Gi0/0 │ │ │ │ │ │ │ │ IP Address: 10.1.1.2│ │ │ │ │ │ └─────────┘ └─────────┘ │ │ │ │ │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ CDP Information: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Device ID (hostname) │ │ │ │ • Platform (hardware model) │ │ │ │ • Local interface │ │ │ │ • Remote interface │ │ │ │ • IP address (management) │ │ │ │ • Capabilities (Router, Switch, Phone, etc.) │ │ │ │ • IOS version │ │ │ │ • VTP domain │ │ │ │ • Native VLAN │ │ │ │ • Duplex mode │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ### 2. CDP Features | Feature | Description | |---------|-------------| | **Layer** | Layer 2 (data link layer) | | **Transport** | Ethernet, Frame Relay, ATM | | **Multicast MAC** | 01:00:0C:CC:CC:CC | | **Default Timer** | 60 seconds between advertisements | | **Default Holdtime** | 180 seconds (3 × timer) | | **Protocol** | Cisco proprietary | | **Information** | Device ID, platform, IP, capabilities, interface, etc. | ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ CDP TIMERS │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ CDP Timers: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ Timer: 60 seconds │ │ │ │ │ │ │ │ │ │ CDP Advertisement │ │ │ │ ▼ │ │ │ │ ┌─────────────────────────────────────────────────────────────────┐│ │ │ │ │ Device A sends CDP advertisement ││ │ │ │ └─────────────────────────────────────────────────────────────────┘│ │ │ │ │ │ │ │ │ │ │ │ │ │ Holdtime: 180 seconds │ │ │ │ │ │ │ │ │ │ Device B holds information for 180 seconds │ │ │ │ │ If no new advertisement within 180 seconds, neighbor removed │ │ │ │ │ │ │ │ │ └─────────────────────────────────────────────────────────────────┘ │ │ │ │ │ │ │ Timer can be adjusted (range: 5-254 seconds) │ │ │ │ Holdtime should be ≥ 3 × timer │ │ │ │ │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ### 3. CDP Configuration **Enable/Disable CDP Globally:** ```cisco ! Enable CDP globally (default is enabled) Router(config)# cdp run ! Disable CDP globally Router(config)# no cdp run ``` **Enable/Disable CDP on Interface:** ```cisco ! Enable CDP on interface (default is enabled) Router(config)# interface gigabitEthernet 0/0 Router(config-if)# cdp enable ! Disable CDP on interface Router(config-if)# no cdp enable ``` **Configure CDP Timers:** ```cisco ! Set CDP timer to 30 seconds (default 60) Router(config)# cdp timer 30 ! Set CDP holdtime to 90 seconds (default 180) Router(config)# cdp holdtime 90 ! Set CDP version (version 2 is default) Router(config)# cdp version 2 ! Enable CDP logging Router(config)# cdp log ``` --- ### 4. CDP Verification Commands | Command | Purpose | |---------|---------| | `show cdp` | Display CDP global settings | | `show cdp neighbors` | Display CDP neighbors summary | | `show cdp neighbors detail` | Display detailed neighbor information | | `show cdp entry [name]` | Display specific neighbor details | | `show cdp interface` | Display CDP-enabled interfaces | | `show cdp traffic` | Display CDP traffic statistics | **Example Outputs:** ```cisco Router# show cdp Global CDP information: Sending CDP packets every 60 seconds Sending a holdtime value of 180 seconds Sending CDPv2 advertisements is enabled Router# show cdp neighbors Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone Device ID Local Intrfce Holdtme Capability Platform Port ID RouterB Gig 0/0 145 R 2911 Gig 0/0 SwitchA Gig 0/1 152 S WS-C3750 Gig 0/24 IPPhone Gig 0/2 168 P CP-7960 Port 1 Router# show cdp neighbors detail ------------------------- Device ID: RouterB Entry address(es): IP address: 10.1.1.2 Platform: Cisco 2911, Capabilities: Router Interface: GigabitEthernet0/0, Port ID (outgoing port): GigabitEthernet0/0 Holdtime: 145 sec Version : Cisco IOS Software, C2900 Software (C2900-UNIVERSALK9-M), Version 15.2(4)M5 ------------------------- Device ID: SwitchA Entry address(es): IP address: 192.168.1.2 Platform: WS-C3750-48PS, Capabilities: Switch Interface: GigabitEthernet0/1, Port ID (outgoing port): GigabitEthernet0/24 Holdtime: 152 sec Version : Cisco IOS Software, C3750 Software (C3750-IPSERVICESK9-M), Version 12.2(55)SE12 ------------------------- Device ID: IPPhone Entry address(es): IP address: 192.168.1.100 Platform: CP-7960, Capabilities: Phone Interface: GigabitEthernet0/2, Port ID (outgoing port): Port 1 Holdtime: 168 sec Version : Cisco IP Phone 7960 ``` --- ### 5. What is LLDP? **Definition:** Link Layer Discovery Protocol (LLDP) is an IEEE standard (802.1AB) Layer 2 protocol that allows network devices to advertise their identity and capabilities to neighbors, similar to CDP but vendor-neutral. **Analogy:** LLDP is like a universal introduction protocol. Unlike CDP (which only Cisco devices understand), LLDP works across all vendors, like a common language everyone speaks. ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ LLDP OPERATION │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ LLDP Advertisement (Multicast MAC 01:80:C2:00:00:0E): │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ Cisco Router HP Switch │ │ │ │ ┌─────────┐ ┌─────────┐ │ │ │ │ │ LLDP │ │ LLDP │ │ │ │ │ │ Agent │ "Hello! I'm Router│ Agent │ │ │ │ │ │ │ Chassis ID: MAC │ │ │ │ │ │ │ │ Port ID: Gi0/0 │ │ │ │ │ │ │ │ System Name: Router│ │ │ │ │ │ │ │ System Desc: Cisco│ │ │ │ │ │ │ │ Capabilities: Router"│ │ │ │ │ │ └─────────┘ ──────────────────► └─────────┘ │ │ │ │ │ │ │ │ Cisco Router HP Switch │ │ │ │ ┌─────────┐ ┌─────────┐ │ │ │ │ │ LLDP │ │ LLDP │ │ │ │ │ │ Agent │ ◄──────────────────│ Agent │ │ │ │ │ │ │ "Hello! I'm Switch│ │ │ │ │ │ │ │ Chassis ID: MAC │ │ │ │ │ │ │ │ Port ID: Gi0/24 │ │ │ │ │ │ │ │ System Name: Switch│ │ │ │ │ │ │ │ Capabilities: Switch"│ │ │ │ │ │ └─────────┘ └─────────┘ │ │ │ │ │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ LLDP Information: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Chassis ID (MAC address) │ │ │ │ • Port ID (interface name) │ │ │ │ • System Name (hostname) │ │ │ │ • System Description (hardware/software) │ │ │ │ • Management IP address │ │ │ │ • Capabilities (Router, Switch, etc.) │ │ │ │ • VLAN ID (802.1) │ │ │ │ • PoE (Power over Ethernet) │ │ │ │ • Link aggregation │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ### 6. LLDP Features | Feature | Description | |---------|-------------| | **Layer** | Layer 2 (data link layer) | | **Transport** | Ethernet | | **Multicast MAC** | 01:80:C2:00:00:0E | | **Default Timer** | 30 seconds between advertisements | | **Default Holdtime** | 120 seconds (4 × timer) | | **Protocol** | IEEE 802.1AB (vendor-neutral) | | **Information** | Chassis ID, port ID, system name, capabilities, management address | **LLDP-MED (Media Endpoint Discovery):** Extension for IP phones and other endpoints ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ LLDP-MED │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ LLDP-MED Extensions for IP Phones: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Capabilities (phone, switch) │ │ │ │ • Network Policy (VLAN ID, DSCP, etc.) │ │ │ │ • Power over Ethernet (power requirements) │ │ │ │ • Inventory (hardware/software version) │ │ │ │ • Location (emergency services) │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ LLDP-MED for IP Phone: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ Switch IP Phone │ │ │ │ ┌─────────┐ ┌─────────┐ │ │ │ │ │ LLDP │ │ LLDP-MED│ │ │ │ │ │ Agent │ "Voice VLAN: 10 │ Agent │ │ │ │ │ │ │ DSCP: 46 │ │ │ │ │ │ │ │ Power: 802.3af" │ │ │ │ │ │ └─────────┘ ─────────────────────► └─────────┘ │ │ │ │ │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ### 7. LLDP Configuration **Enable/Disable LLDP Globally:** ```cisco ! Enable LLDP globally (default is disabled) Router(config)# lldp run ! Disable LLDP globally Router(config)# no lldp run ``` **Enable/Disable LLDP on Interface:** ```cisco ! Enable LLDP on interface Router(config)# interface gigabitEthernet 0/0 Router(config-if)# lldp transmit Router(config-if)# lldp receive ! Disable LLDP on interface Router(config-if)# no lldp transmit Router(config-if)# no lldp receive ``` **Configure LLDP Timers:** ```cisco ! Set LLDP timer to 30 seconds (default 30) Router(config)# lldp timer 30 ! Set LLDP holdtime to 120 seconds (default 120) Router(config)# lldp holdtime 120 ! Set LLDP reinit delay (time before reinitialization) Router(config)# lldp reinit 2 ``` **Configure LLDP-MED:** ```cisco ! Enable LLDP-MED on interface interface GigabitEthernet0/1 lldp med-tlv-select inventory lldp med-tlv-select network-policy lldp med-tlv-select power-management ``` --- ### 8. LLDP Verification Commands | Command | Purpose | |---------|---------| | `show lldp` | Display LLDP global settings | | `show lldp neighbors` | Display LLDP neighbors summary | | `show lldp neighbors detail` | Display detailed neighbor information | | `show lldp entry [name]` | Display specific neighbor details | | `show lldp interface` | Display LLDP-enabled interfaces | | `show lldp traffic` | Display LLDP traffic statistics | | `show lldp local` | Display local LLDP information | **Example Outputs:** ```cisco Router# show lldp Global LLDP Information: Status: ACTIVE LLDP advertisements are sent every 30 seconds LLDP hold time advertised is 120 seconds LLDP interface reinitialization delay is 2 seconds Router# show lldp neighbors Capability codes: (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other Device ID Local Intf Hold-time Capability Port ID 00:1a:2b:3c:4d:5e Gi0/0 110 B Gi0/24 00:1a:2b:3c:4d:5f Gi0/1 115 T Port 1 00:1a:2b:3c:4d:60 Gi0/2 120 R Gi0/0 Router# show lldp neighbors detail ------------------------------------------------ Local Intf: Gi0/0 Chassis id: 00:1a:2b:3c:4d:5e Port id: Gi0/24 Port Description: GigabitEthernet0/24 System Name: SwitchA System Description: Cisco IOS Software, C3750 Software (C3750-IPSERVICESK9-M), Version 12.2(55)SE12 Time remaining: 110 seconds System Capabilities: B, T Enabled Capabilities: B Management Addresses: IP: 192.168.1.2 Auto Negotiation - supported, enabled Physical media capabilities: 1000baseT(FD) 100baseTX(FD) 100baseTX(HD) 10baseT(FD) 10baseT(HD) Media Attachment Unit type: 16 Vlan ID: 1 ------------------------------------------------ Local Intf: Gi0/1 Chassis id: 00:1a:2b:3c:4d:5f Port id: Port 1 Port Description: Port 1 System Name: IPPhone System Description: Cisco IP Phone 7960 Time remaining: 115 seconds System Capabilities: T Enabled Capabilities: T Management Addresses: IP: 192.168.1.100 Power via MDI - Supported Power pairs: Signal Power class: 3 Media Policy: Network Policy for Application: Voice VLAN ID: 10 DSCP Value: 46 Priority Value: 5 ``` --- ### 9. CDP vs. LLDP Comparison | Feature | CDP | LLDP | |---------|-----|------| | **Standard** | Cisco proprietary | IEEE 802.1AB (vendor-neutral) | | **Multicast MAC** | 01:00:0C:CC:CC:CC | 01:80:C2:00:00:0E | | **Default Timer** | 60 seconds | 30 seconds | | **Default Holdtime** | 180 seconds | 120 seconds | | **Enabled by Default** | Yes | No | | **Information** | Device ID, platform, IP, IOS | Chassis ID, port ID, system name, description | | **Voice Support** | CDP (Cisco phones) | LLDP-MED (multi-vendor) | | **Security** | Can be disabled | Can be disabled | | **Use Case** | Cisco-only networks | Multi-vendor networks | ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ CDP vs. LLDP COMPARISON │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ CDP (Cisco): │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Pros: │ │ │ │ • Enabled by default on Cisco devices │ │ │ │ • More detailed Cisco-specific information │ │ │ │ • Better integration with Cisco features (Voice VLAN, etc.) │ │ │ │ • Works with Cisco phones out-of-box │ │ │ │ │ │ │ │ Cons: │ │ │ │ • Only works with Cisco devices │ │ │ │ • Security risk (information disclosure) │ │ │ │ • Not standardized │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ LLDP (IEEE): │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Pros: │ │ │ │ • Vendor-neutral (works with all devices) │ │ │ │ • Standardized (IEEE 802.1AB) │ │ │ │ • LLDP-MED for IP phones (multi-vendor) │ │ │ │ • More secure (disabled by default) │ │ │ │ │ │ │ │ Cons: │ │ │ │ • Disabled by default on Cisco devices │ │ │ │ • Less detailed information than CDP │ │ │ │ • May not support all Cisco-specific features │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ### 10. CDP and LLDP Security **Security Considerations:** ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ CDP/LLDP SECURITY │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ RISKS: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Information disclosure (device types, IP addresses, IOS versions) │ │ │ │ • Attackers can map network topology │ │ │ │ • Potential for DoS attacks via flooding │ │ │ │ • CDP/LLDP can be used for network reconnaissance │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ BEST PRACTICES: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Disable CDP/LLDP on interfaces facing untrusted networks │ │ │ │ • Disable CDP/LLDP on customer-facing ports (service provider) │ │ │ │ • Use CDP/LLDP only where needed (for discovery, phones) │ │ │ │ • Consider using LLDP instead of CDP for multi-vendor networks │ │ │ │ • Regularly audit CDP/LLDP configuration │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ SECURITY CONFIGURATION: │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ ! Disable CDP on WAN interfaces │ │ │ │ interface Serial0/0/0 │ │ │ │ no cdp enable │ │ │ │ │ │ │ │ ! Disable CDP on customer-facing interfaces │ │ │ │ interface GigabitEthernet0/1 │ │ │ │ no cdp enable │ │ │ │ │ │ │ │ ! Disable LLDP globally (if not needed) │ │ │ │ no lldp run │ │ │ │ │ │ │ │ ! Disable LLDP on untrusted interfaces │ │ │ │ interface GigabitEthernet0/2 │ │ │ │ no lldp transmit │ │ │ │ no lldp receive │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ### 11. Use Cases for CDP/LLDP ``` ┌─────────────────────────────────────────────────────────────────────────────┐ │ CDP/LLDP USE CASES │ ├─────────────────────────────────────────────────────────────────────────────┤ │ │ │ USE CASE 1: Network Discovery │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Map network topology │ │ │ │ • Identify neighboring devices │ │ │ │ • Verify physical connections │ │ │ │ • Troubleshoot connectivity issues │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ USE CASE 2: Voice Deployment (IP Phones) │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Auto-detect IP phones (CDP or LLDP-MED) │ │ │ │ • Dynamically assign voice VLAN │ │ │ │ • Apply QoS policies │ │ │ │ • Provide PoE information │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ USE CASE 3: Network Management │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Automatically discover devices in NMS │ │ │ │ • Update network topology maps │ │ │ │ • Track device inventory │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ │ USE CASE 4: Troubleshooting │ │ ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ • Verify neighbor connectivity │ │ │ │ • Identify mismatched configurations │ │ │ │ • Find connected devices │ │ │ │ • Determine device types and capabilities │ │ │ └─────────────────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────────────────────────────────────────────────────────────┘ ``` --- ## 🔧 Complete Configuration Examples ### Lab 1: CDP Configuration ```cisco ! Enable CDP globally cdp run ! Configure CDP timers cdp timer 60 cdp holdtime 180 ! Configure interface-specific CDP interface GigabitEthernet0/0 cdp enable interface GigabitEthernet0/1 no cdp enable ! Disable on untrusted interface ! Verify show cdp show cdp neighbors show cdp interface ``` --- ### Lab 2: LLDP Configuration ```cisco ! Enable LLDP globally lldp run ! Configure LLDP timers lldp timer 30 lldp holdtime 120 ! Configure interface-specific LLDP interface GigabitEthernet0/0 lldp transmit lldp receive interface GigabitEthernet0/1 no lldp transmit no lldp receive ! Verify show lldp show lldp neighbors show lldp interface ``` --- ### Lab 3: LLDP-MED for IP Phones ```cisco ! Enable LLDP globally lldp run ! Configure LLDP-MED on interface interface GigabitEthernet0/2 switchport mode access switchport voice vlan 10 switchport access vlan 20 lldp transmit lldp receive lldp med-tlv-select network-policy lldp med-tlv-select power-management lldp med-tlv-select inventory ! Verify show lldp neighbors detail show lldp interface gigabitEthernet 0/2 ``` --- ### Lab 4: Security Hardening - Disable Discovery Protocols on Untrusted Ports ```cisco ! Global disable CDP no cdp run ! Or disable only on untrusted ports interface GigabitEthernet0/0 no cdp enable ! Global disable LLDP no lldp run ! Or disable on untrusted ports interface GigabitEthernet0/1 no lldp transmit no lldp receive ! Keep CDP/LLDP only where needed interface GigabitEthernet0/24 ! Uplink to core cdp enable lldp transmit lldp receive ``` --- ## ✅ Exam Tips (For CCNA 200-301) | Topic | What Cisco Tests | |-------|------------------| | **CDP** | Cisco proprietary, enabled by default, multicast MAC 01:00:0C:CC:CC:CC | | **LLDP** | IEEE standard, disabled by default, multicast MAC 01:80:C2:00:00:0E | | **CDP Timers** | 60 sec (timer), 180 sec (holdtime) | | **LLDP Timers** | 30 sec (timer), 120 sec (holdtime) | | **CDP Show Commands** | `show cdp neighbors`, `show cdp neighbors detail` | | **LLDP Show Commands** | `show lldp neighbors`, `show lldp neighbors detail` | | **LLDP-MED** | Extension for IP phones and endpoints | ### Common Exam Scenarios: **Scenario 1:** "A network administrator needs to discover neighboring Cisco devices. Which protocol should be used?" - **Answer:** CDP (Cisco Discovery Protocol) **Scenario 2:** "A network has both Cisco and HP switches. Which discovery protocol should be used for interoperability?" - **Answer:** LLDP (Link Layer Discovery Protocol) **Scenario 3:** "What is the default CDP holdtime?" - **Answer:** 180 seconds ### Mnemonics: **CDP/LLDP Multicast MACs:** **"Cisco CDP: 01:00:0C:CC:CC:CC"** **"LLDP: 01:80:C2:00:00:0E"** **CDP Timers:** **"60 and 180"** - Timer: 60 seconds - Holdtime: 180 seconds **LLDP Timers:** **"30 and 120"** - Timer: 30 seconds - Holdtime: 120 seconds --- ## 📝 Summary (1-Minute Revision) ``` CDP (Cisco Discovery Protocol): FEATURES: ├── Cisco proprietary ├── Enabled by default ├── Multicast MAC: 01:00:0C:CC:CC:CC ├── Timer: 60 sec, Holdtime: 180 sec └── Information: Device ID, platform, IP, IOS, interface COMMANDS: ├── cdp run / no cdp run (global) ├── cdp enable / no cdp enable (interface) ├── cdp timer [seconds] ├── cdp holdtime [seconds] └── show cdp neighbors LLDP (Link Layer Discovery Protocol): FEATURES: ├── IEEE 802.1AB (vendor-neutral) ├── Disabled by default ├── Multicast MAC: 01:80:C2:00:00:0E ├── Timer: 30 sec, Holdtime: 120 sec └── Information: Chassis ID, port ID, system name, capabilities COMMANDS: ├── lldp run / no lldp run (global) ├── lldp transmit / lldp receive (interface) ├── lldp timer [seconds] ├── lldp holdtime [seconds] └── show lldp neighbors LLDP-MED: ├── Extension for IP phones ├── Voice VLAN, DSCP, PoE information └── Used for multi-vendor voice deployments SECURITY: ├── Disable on untrusted interfaces ├── Disable on customer-facing ports └── Use only where needed VERIFICATION: ├── show cdp neighbors ├── show cdp neighbors detail ├── show lldp neighbors └── show lldp neighbors detail ``` --- ## 🧪 Practice Questions **1. Which multicast MAC address does CDP use?** - A) 01:00:0C:CC:CC:CC - B) 01:80:C2:00:00:0E - C) 01:00:5E:00:00:01 - D) FF:FF:FF:FF:FF:FF <details> <summary>Answer</summary> <b>A) 01:00:0C:CC:CC:CC</b> - CDP uses multicast MAC address 01:00:0C:CC:CC:CC. </details> **2. What is the default CDP timer value?** - A) 30 seconds - B) 60 seconds - C) 90 seconds - D) 120 seconds <details> <summary>Answer</summary> <b>B) 60 seconds</b> - CDP advertisements are sent every 60 seconds by default. </details> **3. Which command displays detailed CDP neighbor information?** - A) `show cdp` - B) `show cdp neighbors` - C) `show cdp neighbors detail` - D) `show cdp entry` <details> <summary>Answer</summary> <b>C) `show cdp neighbors detail`</b> - Displays detailed information about CDP neighbors. </details> **4. Is CDP enabled or disabled by default on Cisco devices?** - A) Disabled - B) Enabled - C) Depends on the model - D) Depends on the IOS version <details> <summary>Answer</summary> <b>B) Enabled</b> - CDP is enabled by default on Cisco devices. </details> **5. Which protocol is vendor-neutral and defined by IEEE 802.1AB?** - A) CDP - B) LLDP - C) VTP - D) STP <details> <summary>Answer</summary> <b>B) LLDP</b> - Link Layer Discovery Protocol is defined by IEEE 802.1AB. </details> **6. What is the default LLDP timer value?** - A) 30 seconds - B) 60 seconds - C) 90 seconds - D) 120 seconds <details> <summary>Answer</summary> <b>A) 30 seconds</b> - LLDP advertisements are sent every 30 seconds by default. </details> **7. Which command enables LLDP globally?** - A) `lldp enable` - B) `lldp run` - C) `cdp run` - D) `lldp start` <details> <summary>Answer</summary> <b>B) `lldp run`</b> - This command enables LLDP globally on Cisco devices. </details> **8. What does LLDP-MED provide that standard LLDP does not?** - A) Device ID - B) Port ID - C) Voice VLAN and PoE information - D) System name <details> <summary>Answer</summary> <b>C) Voice VLAN and PoE information</b> - LLDP-MED adds extensions for IP phones and endpoints. </details> **9. Which command displays LLDP neighbors?** - A) `show lldp` - B) `show lldp neighbors` - C) `show lldp info` - D) `show lldp entries` <details> <summary>Answer</summary> <b>B) `show lldp neighbors`</b> - Displays summary of LLDP neighbors. </details> **10. What is a security risk of leaving CDP enabled on untrusted interfaces?** - A) Denial of service - B) Information disclosure (network topology) - C) Authentication bypass - D) Encryption failure <details> <summary>Answer</summary> <b>B) Information disclosure (network topology)</b> - CDP reveals device information that attackers can use for reconnaissance. </details> **11. Which command disables CDP on an interface?** - A) `no cdp run` - B) `no cdp enable` - C) `cdp disable` - D) `no cdp` <details> <summary>Answer</summary> <b>B) `no cdp enable`</b> - Disables CDP on a specific interface. </details> **12. What is the default CDP holdtime?** - A) 60 seconds - B) 120 seconds - C) 180 seconds - D) 240 seconds <details> <summary>Answer</summary> <b>C) 180 seconds</b> - CDP holdtime is 180 seconds (3 × timer). </details> --- ## 📌 Next Steps After completing Video 46, you should be ready for: - **Video 47:** NTP and SNMP (Advanced) - **Video 48:** NetFlow and IPFIX **Lab Practice:** 1. Configure CDP on a router and switch 2. Verify neighbors with `show cdp neighbors` 3. Configure LLDP on a router 4. Verify LLDP neighbors with `show lldp neighbors` 5. Disable CDP on untrusted interfaces 6. Configure LLDP-MED for IP phones 7. Compare CDP and LLDP information --- **Ready for Video 47?** Share the link or say "next" and I'll continue with NTP and SNMP (Advanced). I'll continue with **Video 47: NTP and SNMP (Advanced)** based on the standard CCNA 200-301 curriculum. ---