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Understanding VXLAN BGP EVPN Packet Flows

Mar 6, 2025

Cisco Live Lecture Notes

Date: Unknown
Speaker: Lucas Cradiger
Topic: Day in the Life of a Packet in VXLAN BGP EVPN Fabric

Introduction

  • Final day of Cisco Live.
  • Session split: single fabric in the morning, multi-site setup later.
  • Session level: Intermediate to Advanced.
  • Interactive Q&A via WebEx Teams.
  • Lecture focus: Detailed packet walks through VXLAN BGP EVPN fabric.
  • Key concepts: routing, bridging, silent host discovery, BUM (Broadcast, Unknown-Unicast, Multicast) traffic.

Key Topics

VXLAN and EVPN Overview

  • VXLAN: Encapsulation method, data plane.
  • EVPN: Control plane using BGP, manages routing, bridging, and BUM handling.
  • Data Plane vs. Control Plane: Control plane defines actions for the data plane.

Network Device Structure

  • Overview of network devices (spines, leaves) and their roles in packet forwarding.
  • VTEP (VXLAN Tunnel Endpoint): Enables network virtualization.
  • Tables:
    • Mac Table: For Layer 2 info learning.
    • ARP Table: Maps MAC to IP.
    • RIP and FIB tables: Software and hardware routing tables.

Packet Walkthroughs

  • Routing and Bridging Process: Detailed step-by-step of encapsulation, routing, and bridging of packets.
  • Control Plane Operations: How advertisements and route type learning occur via BGP.
  • Forwarding Table Construction: How tables are used for routing and bridging decisions.

Detailed Packet Scenarios

  1. Host to External Network: Understanding route type 5 and learning process via advertisements.
  2. External Network to Host: Reverse of the above process.
  3. Host to Host Routing: Use of routing tables and route types for internal communication.
  4. Host to Host Bridging: Focus on MAC addresses, no change in source/destination MAC.
  5. BUM Traffic Handling:
    • Ingress Replication: Head-end replicates packets to all relevant VTEPs.
    • Multicast Replication: Utilizes PIM for packet distribution.

Silent Host Discovery

  • Challenge: Finding dormant hosts that have not communicated recently.
  • Solution: Glean process using ARP requests to wake up hosts and initiate communication.
  • Advantage: Prevents unknown unicast flooding by maintaining active host tables.

Conclusion

  • Recap of various packet walks and scenarios.
  • Emphasis on the importance of understanding packet flows for network operation.
  • Encouragement for feedback and further questions.

Additional Resources

  • Mention of further sessions and materials available for deeper dives into topics discussed.

Full transcript