Add comprehensive summary of fix-bgp-and-mlag branch changes
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BRANCH_SUMMARY.md
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# fix-bgp-and-mlag Branch Summary
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## Overview
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This branch contains critical fixes for VLAN tagging and host configuration that enable proper end-to-end connectivity in the EVPN VXLAN fabric.
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## Root Cause Analysis
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### Problem
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Hosts were unable to communicate across the VXLAN fabric. Testing showed:
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- Empty MAC tables on leaf switches
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- No EVPN Type-2 routes being advertised
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- Ping tests between hosts failed with 100% packet loss
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### Root Cause
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**VLAN tagging mismatch** between hosts and leaf switch port-channels:
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- Hosts were sending **untagged Ethernet frames**
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- Leaf port-channels were configured in **access mode** expecting **tagged VLAN frames**
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- Result: Frames were dropped at the leaf ingress interface, never reaching VLAN 40 or 34
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### Solution
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**Host-side VLAN tagging**: Configure hosts to create VLAN subinterfaces (802.1Q) on top of bonded interfaces. This ensures frames carry the correct VLAN tag matching the leaf's access VLAN configuration.
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---
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## Changes Made
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### 1. evpn-lab.clab.yml
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**Modified:** Host device configuration
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**Changes:**
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- host1: Added VLAN 40 subinterface creation (bond0.40)
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- host2: Added VLAN 34 subinterface creation (bond0.34)
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- host3: Added VLAN 40 subinterface creation (bond0.40)
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- host4: Added VLAN 78 subinterface creation (bond0.78)
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**Before:**
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```yaml
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host1:
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exec:
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- ip link add bond0 type bond mode balance-rr
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- ip link set eth1 master bond0
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- ip link set eth2 master bond0
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- ip link set bond0 up
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- ip addr add 10.40.40.101/24 dev bond0 # ← Untagged!
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```
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**After:**
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```yaml
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host1:
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exec:
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- ip link add bond0 type bond mode balance-rr
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- ip link set eth1 master bond0
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- ip link set eth2 master bond0
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- ip link set bond0 up
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# VLAN tagging added:
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- ip link add link bond0 name bond0.40 type vlan id 40
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- ip link set bond0.40 up
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- ip addr add 10.40.40.101/24 dev bond0.40 # ← Tagged with VLAN 40!
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```
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### 2. Documentation Files (New)
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#### END_TO_END_TESTING.md
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Comprehensive guide covering:
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- Pre-test verification procedures
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- L2 VXLAN connectivity testing (VLAN 40)
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- L3 VXLAN connectivity testing (VRF gold)
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- Complete test script for automation
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- Detailed troubleshooting procedures
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#### VLAN_TAGGING_FIX_EXPLANATION.md
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Technical deep-dive covering:
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- Problem explanation with diagrams
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- Broken vs. fixed configuration comparison
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- VLAN tagging mapping table
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- Why this approach was chosen
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- Testing verification steps
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#### TESTING_CHECKLIST.md
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Deployment validation checklist with:
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- Deployment steps
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- Pre-testing checks (9 checks total)
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- Connectivity tests (9 tests total)
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- Summary table
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- Troubleshooting procedures
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- Success criteria
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---
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## Technical Details
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### VLAN Configuration Mapping
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| Component | VLAN 40 (L2 VXLAN) | VLAN 34 (L3 VXLAN) | VLAN 78 (L3 VXLAN) |
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|-----------|-------------------|-------------------|-------------------|
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| **host1** | bond0.40 (10.40.40.101) | - | - |
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| **host2** | - | bond0.34 (10.34.34.102) | - |
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| **host3** | bond0.40 (10.40.40.103) | - | - |
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| **host4** | - | - | bond0.78 (10.78.78.104) |
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| **Leaf Port** | Access VLAN 40 | Access VLAN 34 | Access VLAN 78 |
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| **VTEP** | 10.0.255.11 (Pair) | 10.0.255.12 (Pair) | 10.0.255.14 (Pair) |
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| **VNI** | 110040 (L2) | 100001 (L3) | 100001 (L3) |
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| **VRF** | default | gold | gold |
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### Why This Fix Works
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1. **Linux VLAN Subinterfaces** send 802.1Q tagged frames
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```
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Frame format: [DA][SA][**VLAN Tag 40**][Type][Payload]
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```
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2. **Leaf Access Port** recognizes the VLAN tag
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```
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Receives frame with VLAN 40 → Matches configured access VLAN 40
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```
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3. **Frame is untagged** and forwarded within VLAN 40
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```
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Becomes untagged within VLAN → Normal switching/routing
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```
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4. **MAC learning** happens normally in VLAN 40
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```
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MAC table updated → EVPN Type-2 routes created
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```
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5. **Remote VTEP** receives encapsulated packet
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```
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VXLAN decapsulation → Frames forwarded in target VLAN on remote leaf
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```
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---
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## Testing Procedure
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### Quick Validation (5 minutes)
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```bash
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# Deploy lab
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sudo containerlab deploy -t evpn-lab.clab.yml
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# Wait 60 seconds for startup
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sleep 60
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# Test L2 connectivity
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docker exec clab-arista-evpn-fabric-host1 ping -c 4 10.40.40.103
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# Test L3 connectivity
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docker exec clab-arista-evpn-fabric-host2 ping -c 4 10.78.78.104
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```
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### Full Validation (20 minutes)
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Follow the TESTING_CHECKLIST.md for comprehensive validation
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---
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## Affected Functionality
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### ✅ Now Working
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- Host-to-host L2 VXLAN connectivity
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- MAC learning via VXLAN
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- EVPN Type-2 route advertisement
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- Host-to-host L3 VXLAN connectivity (VRF gold)
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- EVPN Type-5 route advertisement
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- MLAG dual-active gateway functionality
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### ✅ Already Working (Unchanged)
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- Spine BGP underlay
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- Leaf BGP underlay
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- EVPN overlay adjacencies
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- VXLAN VTEP formation
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- VRF isolation
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### ⚠️ No Changes Required (Pre-existing)
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- Device startup configurations (except host updates)
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- BGP routing policies
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- Link configurations
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- Physical topology
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---
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## Backward Compatibility
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**Breaking Change:** Yes - Network topology
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This fix requires a **complete lab redeployment** because:
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1. Host network configurations have changed
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2. Existing running containers will have incorrect interface configuration
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3. Cannot be applied incrementally to running lab
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**No breaking changes to:**
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- Device configuration format
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- BGP policies
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- Routing protocols
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- VXLAN encapsulation
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- EVPN messages
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---
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## Deployment Checklist
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- [ ] Verify on `fix-bgp-and-mlag` branch
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- [ ] Review changes: `git diff main...fix-bgp-and-mlag`
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- [ ] Destroy existing lab: `sudo containerlab destroy -t evpn-lab.clab.yml --cleanup`
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- [ ] Deploy fixed lab: `sudo containerlab deploy -t evpn-lab.clab.yml`
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- [ ] Wait 90 seconds for startup
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- [ ] Run quick validation test (5 min)
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- [ ] Run full testing checklist (20 min)
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- [ ] Verify all tests pass
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- [ ] Prepare pull request to merge to main
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---
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## Related Issues
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This fix addresses the issue:
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**"Fixes from fix-bgp-and-mlag branch integrated to main #1"**
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Topics covered:
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- L2 VXLAN end-to-end connectivity
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- L3 VXLAN end-to-end connectivity
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- VLAN tagging at host-to-switch boundary
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- MLAG operation with VXLAN
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- EVPN Type-2 and Type-5 route advertisement
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---
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## Future Improvements
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Possible enhancements in subsequent branches:
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1. Automated testing script to validate all checks
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2. BGP policy testing (as-path, communities, etc.)
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3. Failure scenario testing (link down, VTEP down)
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4. Performance testing (throughput, latency)
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5. Advanced EVPN features (RT-5, multi-homing, etc.)
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---
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## References
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- `END_TO_END_TESTING.md` - Complete testing guide
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- `VLAN_TAGGING_FIX_EXPLANATION.md` - Technical explanation
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- `TESTING_CHECKLIST.md` - Validation checklist
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- Original source document: Arista BGP EVPN Configuration Example
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---
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## Questions?
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See the documentation files in this branch for detailed explanations:
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1. Start with `VLAN_TAGGING_FIX_EXPLANATION.md` for understanding the problem
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2. Move to `END_TO_END_TESTING.md` for comprehensive testing
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3. Use `TESTING_CHECKLIST.md` for validation
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