Link aggregation

2.2 Given a scenario, configure switching technologies and features

Interface Configuration

📘CompTIA Network+ (N10-009)

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Definition:
Link aggregation is a networking technique where multiple physical network connections (ports) are combined into a single logical link. This increases bandwidth and provides redundancy. Think of it as making multiple connections act as one “super-connection” between devices like switches, servers, or routers.

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Why Use Link Aggregation?

1. Higher Bandwidth:
   • A single Ethernet link might be 1 Gbps. Combining four links can give you 4 Gbps of total throughput.
   • Useful when a server or switch needs more bandwidth than a single port can provide.
2. Redundancy / Fault Tolerance:
   • If one physical link fails, traffic can continue over the remaining links.
   • This prevents network downtime and keeps services running.
3. Load Balancing:
   • Network traffic can be spread across all links in the aggregated group.
   • Reduces congestion and improves performance.

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Key Terms You Must Know for the Exam

1. LAG (Link Aggregation Group):
   • A set of physical links bundled together as one logical connection.
   • Example: Ports 1, 2, and 3 on a switch could be grouped into LAG 1.
2. EtherChannel (Cisco terminology):
   • Cisco’s proprietary name for link aggregation.
   • Functions similarly to LAG and is commonly tested in Cisco-related questions.
3. Static vs Dynamic Aggregation:
   • Static:
     • Manually configure the links to be aggregated.
     • All links must match speed, duplex, and VLAN configuration.
   • Dynamic:
     • Uses a protocol to automatically negotiate aggregation between devices.
     • Common protocols: LACP (Link Aggregation Control Protocol)
       • Part of the IEEE 802.3ad standard.
       • Ensures both ends of the link agree on which links to aggregate.
4. LACP (Link Aggregation Control Protocol):
   • Standard protocol used to dynamically create and manage link aggregation.
   • Works across devices from different vendors (multi-vendor support).
   • Provides automatic failover if a link fails.

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How Link Aggregation Works

1. Multiple ports (e.g., 4 ports on a switch) are grouped.
2. The group behaves as a single logical link.
3. Data is spread across the links (load balancing).
4. If one link fails, traffic continues over the remaining links without interruption.

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Requirements for Link Aggregation

• Same speed and duplex: All links in the group must have the same configuration (e.g., all 1 Gbps, full-duplex).
• Same VLANs: All ports in the group must carry the same VLANs.
• Supported hardware/software: Switches, servers, and NICs must support aggregation and LACP if using dynamic mode.

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Exam Tips

1. Know the purpose of link aggregation: bandwidth, redundancy, load balancing.
2. Remember the difference between static and dynamic aggregation.
3. Know LACP is the standard protocol (IEEE 802.3ad) for dynamic link aggregation.
4. Be familiar with Cisco’s term EtherChannel, which works the same way as LAG.
5. Understand real-world IT usage: used between servers and switches, switch to switch, or high-traffic devices.

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Simple Diagram Concept

 Server
 ┌───────────┐
 │ NIC Port1 │════╗
 │ NIC Port2 │════╣
 │ NIC Port3 │════╣   Logical Link (LAG/EtherChannel)
 │ NIC Port4 │════╝
 └───────────┘
       │
       │
      Switch
 ┌─────────────┐
 │ Port1-4 LAG │
 └─────────────┘

• Multiple physical NIC ports on a server connect to multiple switch ports.
• Together, they form one high-speed logical link.

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Quick Summary for Exam

Feature	Description
Link Aggregation	Combines multiple physical links into a single logical link.
Purpose	Increase bandwidth, redundancy, and load balancing.
Static Aggregation	Manually configured; no negotiation protocol.
Dynamic Aggregation	Uses LACP to automatically form a group; IEEE 802.3ad standard.
Cisco Term	EtherChannel
Requirements	Same speed, duplex, VLANs; supported devices.

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✅ Key Takeaway:
Link aggregation is essential in IT environments where high traffic, redundancy, and reliable network performance are required. On the exam, focus on the purpose, configuration types (static/dynamic), and common protocols like LACP.

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