BGP EVPN route types - Type-1 per ESI & Per EVI

⚙️ EVPN Background

In BGP EVPN, several route types are used:

Route Type	Name	Purpose
Type 1	Ethernet Auto-Discovery (EAD)	Used for ESI advertisement & mass-withdrawal
Type 2	MAC/IP Advertisement	Advertise MAC and IP reachability
Type 3	Inclusive Multicast Ethernet Tag (IMET)	Used for BUM traffic flooding trees
Type 4	Ethernet Segment (ES) Route	Used for DF election
Type 5	IP Prefix Route	For inter-subnet / L3 EVPN routes

Now within Type 1 (EAD), there are two “flavors”:

Per-ESI Route
Per-EVI Route

🧩 What is “EVI”?

EVI (Ethernet VPN Instance) → represents one broadcast domain, usually a VLAN or VNI.

So:

One ESI = shared Ethernet Segment (multi-homed link to a host or server).
One EVI = one VLAN/VNI associated with that ESI.

🧭 Type-1 Route Variants

Variant	Field	Scope	Purpose
Per-ESI Route	Ethernet Tag = 0	Global for the whole ESI	Tells everyone “I’m part of this ESI.” Used for multi-homing discovery & mass withdrawal.
Per-EVI Route	Ethernet Tag ≠ 0 (VLAN/VNI ID)	Per VLAN or EVI	Tells everyone “this ESI is active for this specific VLAN.” Used for DF election, MAC flush, etc.

📘 Example

Let’s take an EVPN multihoming setup:


       +--------- Spine (RR) ---------+
       |                              |
   +---+---+                      +---+---+
   | Leaf1 |                      | Leaf2 |
   +---+---+                      +---+---+
       |                              |
   ========= Shared Link ========= (ESI=10)
                to HostA

HostA is connected to both Leaf1 and Leaf2 (multi-homed).
We have two VLANs:

VLAN 10 → EVI 10 (VNI 10100)
VLAN 20 → EVI 20 (VNI 10200)

🔹 Step 1 – Per-ESI Route (Ethernet Tag = 0)

Both Leaf1 and Leaf2 advertise:


Route-Type 1: Per-ESI (Ethernet Tag = 0)
ESI = 10
Label = <per-ESI label>

➡️ Purpose:

To tell remote PEs: “Leaf1 and Leaf2 share the same ESI 10.”
Used for mass withdrawal when ESI fails.

🔹 Step 2 – Per-EVI Routes (Ethernet Tag = VLAN 10, 20)

For each VLAN on that ESI, both PEs also advertise:


Route-Type 1: Per-EVI
ESI = 10
Ethernet Tag = 10   ← VLAN 10
Label = <per-EVI label>

Route-Type 1: Per-EVI
ESI = 10
Ethernet Tag = 20   ← VLAN 20
Label = <per-EVI label>

➡️ Purpose:

Indicates that this ESI participates in this VLAN (EVI).
Used by remote PEs to:
- Associate MAC/IP routes correctly.
- Handle DF election on a per-VLAN basis.

🧠 When they’re used

Function	Per-ESI	Per-EVI
Discover multi-homed PEs	✅	✅
Mass withdrawal (ESI failure)	✅	❌
DF election per VLAN	❌	✅
MAC/IP association	✅	✅
VLAN-specific redundancy	❌	✅

🧩 Example in words

“Leaf1 and Leaf2 advertise a per-ESI route for ESI 10 saying:
We are both part of the same multi-homed segment.

Then, for each VLAN on that segment, they advertise per-EVI routes saying:
For VLAN 10, I’m active on ESI 10. For VLAN 20, same.

If the link goes down on Leaf1, it withdraws the per-ESI route → triggers mass withdrawal.
But DF election or VLAN-specific activity is controlled using the per-EVI routes.”

✅ Quick Summary Table

Route Type 1 Variant	Ethernet Tag	Triggered When	Used For
Per-ESI	0	ESI up/down	Discovery + Mass Withdrawal
Per-EVI	VLAN/VNI ID	VLAN participation	DF Election + VLAN-specific info

Would you like me to show a real BGP EVPN route-table example (from FRR or Arista) that shows both Per-ESI and Per-EVI entries side by side?

Perfect 👌 — let’s walk through a realistic EVPN route table example (like what you’d see on Arista EOS, FRR, or Juniper EVPN) and highlight where per-ESI and per-EVI routes appear.

🧭 Lab Setup (for reference)


        +----------- Spine (RR) -----------+
        |                                 |
     +--+--+                           +--+--+
     |Leaf1|                           |Leaf2|
     +--+--+                           +--+--+
        |                                 |
        +--------- Shared Link -----------+
                  (ESI = 10)
                      |
                   +------+
                   |HostA |
                   +------+
       VLAN 10 → EVI 10 (VNI 10100)
       VLAN 20 → EVI 20 (VNI 10200)

📘 1. Per-ESI Route (Ethernet Tag = 0)

Advertised once per ESI by each PE that’s part of the multihomed segment.
Used for ES discovery and mass withdrawal.

Example output (simplified)


Leaf1# show bgp l2vpn evpn route-type 1
Route Distinguisher: 10.10.10.1:1
  EVPN type-1 (Ethernet A-D per ESI)
  ESI: 0000:0000:0000:0000:000010
  Ethernet Tag ID: 0
  MPLS Label1: 1000
  Next Hop: 10.10.10.1
  Extended communities:
    - ESI Label: 1000
    - ES-Import RT: 0000:0000:0000:0000:000010

Same route from Leaf2:


Route Distinguisher: 10.10.10.2:1
  EVPN type-1 (Ethernet A-D per ESI)
  ESI: 0000:0000:0000:0000:000010
  Ethernet Tag ID: 0
  MPLS Label1: 2000
  Next Hop: 10.10.10.2

➡️ Interpretation:

Ethernet Tag = 0 → Per-ESI route
Both Leaf1 and Leaf2 advertise it.
Used for:
- ESI discovery (they share same ESI)
- Mass withdrawal when one link fails.

📘 2. Per-EVI Route (Ethernet Tag = VLAN/VNI ID)

Advertised once per VLAN (EVI) participating on that ESI.
Used for DF election and VLAN-specific redundancy.

Example output (VLAN 10)


Route Distinguisher: 10.10.10.1:10
  EVPN type-1 (Ethernet A-D per EVI)
  ESI: 0000:0000:0000:0000:000010
  Ethernet Tag ID: 10          ← VLAN 10
  MPLS Label1: 1010
  Next Hop: 10.10.10.1
  Extended communities:
    - ESI Label: 1010
    - ES-Import RT: 0000:0000:0000:0000:000010

Example output (VLAN 20)


Route Distinguisher: 10.10.10.1:20
  EVPN type-1 (Ethernet A-D per EVI)
  ESI: 0000:0000:0000:0000:000010
  Ethernet Tag ID: 20          ← VLAN 20
  MPLS Label1: 1020
  Next Hop: 10.10.10.1

➡️ Interpretation:

Ethernet Tag = VLAN ID (non-zero) → Per-EVI route
Used for:
- DF election (deciding which leaf forwards BUM traffic for VLAN 10/20)
- VLAN-specific failover.

🧠 Putting it all together

Route Variant	Ethernet Tag	Advertised by	Used for	Withdrawn when
Per-ESI	0	Once per ESI	Discovery, Mass Withdrawal	ESI link failure
Per-EVI	VLAN ID	Once per VLAN per ESI	DF Election, VLAN redundancy	VLAN removed or PE shutdown

⚡ After a Link Failure (Leaf1 → HostA down)

On Leaf1:

Withdraws Per-ESI route → remote PEs flush all MACs learned via Leaf1.
Leaf2’s Per-EVI routes remain active → Leaf2 becomes DF and forwards traffic.

✅ Summary

Concept	Example Value	Key Use
Per-ESI Route	Ethernet Tag = 0	“I’m part of this multihomed ESI” → mass withdrawal
Per-EVI Route	Ethernet Tag = VLAN/VNI	“This VLAN participates on this ESI” → DF election per VLAN

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