BUGFIX_EVPN_ACTIVATION.md

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+# BGP EVPN Activation Bug - Critical Fix
+
+## Issue Description
+
+All BGP EVPN neighbors on the leaves were stuck in **Active** state instead of **Established** state, with **0 messages sent/received**.
+
+```
+Neighbor   V AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down State   PfxRcd PfxAcc
+10.0.250.1 4 65000              0         0    0    0 00:02:05 Active
+10.0.250.2 4 65000              0         0    0    0 00:02:05 Active
+```
+
+Active state with 0 messages means the TCP handshake was **never completed**.
+
+## Root Cause
+
+The **spine BGP configurations were missing the EVPN address family activation**.
+
+In both `configs/spine1.cfg` and `configs/spine2.cfg`:
+
+```
+address-family evpn
+   neighbor evpn activate     ← This line was MISSING!
+```
+
+Without activating the EVPN address family on the spines, they:
+1. Accept the EVPN neighbor definitions
+2. But don't actively listen for or respond to EVPN connections
+3. Leaves try to establish sessions but spines don't respond
+4. Connection attempt times out → Active state
+
+This is **different from the IPv4 underlay** which was working because the IPv4 address family **was activated** on the spines.
+
+## Solution Applied
+
+### Before (Broken)
+```
+router bgp 65000
+   ...
+   address-family evpn
+      ! Missing activation line!
+```
+
+### After (Fixed)
+```
+router bgp 65000
+   ...
+   address-family evpn
+      neighbor evpn activate
+```
+
+## Files Modified
+
+- `configs/spine1.cfg` - Added `neighbor evpn activate` in EVPN address family
+- `configs/spine2.cfg` - Added `neighbor evpn activate` in EVPN address family
+
+## Technical Explanation
+
+In Arista EOS BGP, neighbors defined in the global BGP context don't actively participate in any address family **until explicitly activated in that address family block**.
+
+### Address Family Activation Rules
+
+```
+router bgp 65000
+   neighbor 10.0.250.1 peer group evpn
+   neighbor 10.0.250.1 remote-as 65000
+   
+   address-family evpn
+      neighbor evpn activate  ← REQUIRED for EVPN sessions to work
+   
+   address-family ipv4
+      neighbor 10.0.250.1 activate  ← Separate activation for IPv4
+```
+
+Without activating in the EVPN address family:
+- The spines define the neighbor parameters ✓
+- The spines enter BGP configuration ✓
+- The spines do NOT listen on TCP 179 for EVPN sessions ✗
+- Leaf attempts to TCP connect to spine loopback on port 179 for EVPN ✗
+- Timeout occurs → Active state ✗
+
+## Testing the Fix
+
+After deploying with the fix, the EVPN neighbors should immediately transition to **Established**:
+
+```bash
+# Before fix
+10.0.250.1 4 65000 0 0 0 0 00:02:05 Active
+
+# After fix
+10.0.250.1 4 65000 8 8 0 0 00:00:15 Estab
+```
+
+## Impact
+
+This was a **critical bug** that:
+- Prevented any EVPN overlay from functioning
+- Made L2 VXLAN testing impossible
+- Made L3 VXLAN testing impossible
+- Prevented MAC learning via VXLAN
+- Prevented EVPN route distribution
+
+Once fixed, the entire EVPN overlay becomes operational immediately.
+
+## Lesson Learned
+
+In BGP multi-address-family configurations, **every address family must be explicitly activated**. This includes:
+- IPv4 unicast
+- IPv6 unicast  
+- EVPN
+- Route target filtering
+- Any other address families being used
+
+A common mistake is to define a neighbor globally but forget to activate it in all address families where it should be used.