5 · EVPN Route Types 1, 2, 3, 4, & 5 Deep Dive¶
BGP EVPN (RFC 7432 / RFC 8214 / RFC 9135) uses MP-BGP Address Family AFI 25 (L2VPN) / SAFI 70 (EVPN). The EVPN NLRI encodes five standardized Route Types.
EVPN Route Types Summary Matrix¶
| Type | Name | Primary Purpose | Key NLRI Fields | Key Extended Communities |
|---|---|---|---|---|
| Route Type 1 | Ethernet Auto-Discovery (A-D) | Fast Failover (Mass Withdraw), Aliasing, ESI Split Horizon | ESI (10B), Ethernet Tag ID, MPLS/VNI Label | ESI Label, Redundancy Mode |
| Route Type 2 | MAC / IP Advertisement | Host reachability (MAC + IP), ARP Proxy | ESI, MAC Address (6B), IP Address (4B/16B), VNI | Router MAC, Default Gateway |
| Route Type 3 | Inclusive Multicast (IMET) | VTEP Discovery & BUM Flood List | Ethernet Tag ID, Origin VTEP IP | Layer 2 VNI |
| Route Type 4 | Ethernet Segment Route | PE Discovery & Designated Forwarder (DF) Election | ESI (10B), Origin VTEP IP | ES Import Route Target |
| Route Type 5 | IP Prefix Route | Inter-Subnet VRF Routing (L3VNI), Summary / Default Routes | IP Prefix / Length, Gateway IP | Router MAC, Layer 3 VNI |
1. Route Type 2 · MAC/IP Advertisement (Host Reachability)¶
Route Type 2 is the core workhorse of BGP EVPN. When a local leaf switch discovers a host MAC or IP via ARP / DHCP / Data-Plane frame arrival, it advertises a Type 2 route into MP-BGP:
Route Type 2 NLRI Structure:
+------------------------------------------+
| Route Distinguisher (8 bytes) |
| Ethernet Segment Identifier (10 bytes) |
| Ethernet Tag ID (4 bytes) |
| MAC Address Length (1 byte) |
| MAC Address (6 bytes) |
| IP Address Length (1 byte - 0, 32, 128) |
| IP Address (0, 4, or 16 bytes) |
| MPLS/VNI Label 1 (3 bytes - L2VNI) |
| MPLS/VNI Label 2 (3 bytes - L3VNI) |
+------------------------------------------+
Key Functions¶
- Control-Plane MAC Learning: Replaces data-plane flood-and-learn over WAN/Backbone.
- ARP Suppression: Allows remote leafs to answer host ARP requests locally out of their BGP EVPN host table without flooding ARP Broadcasts across the fabric!
- MAC Mobility: Tracks host movement between VTEPs using a Sequence Number Extended Community.
2. Route Type 3 · Inclusive Multicast Ethernet Tag (IMET)¶
When a VTEP brings up a Layer 2 VNI, it immediately advertises a Type 3 route:
Route Type 3 NLRI Structure:
+------------------------------------------+
| Route Distinguisher (8 bytes) |
| Ethernet Tag ID (4 bytes) |
| Originating Router IP Length (1 byte) |
| Originating Router IP (4 bytes) |
+------------------------------------------+
- Purpose: Discovers remote VTEPs participating in the same VNI and builds the Headend Unicast Replication List for BUM traffic.
3. Route Type 5 · IP Prefix Route (Inter-Subnet Routing)¶
Type 5 routes advertise IP subnets (10.100.0.0/16) or default routes (0.0.0.0/0) attached to an L3VNI VRF, independent of MAC addresses.
graph LR
Leaf1["leaf1 (VTEP 1)<br/>Advertises Subnet 10.100.1.0/24"] ===>|Type 5 Route + L3VNI 50001| SpineRR["Spine Route Reflector"]
SpineRR ===>|Reflects Type 5| Leaf2["leaf2 (VTEP 2)<br/>Installs 10.100.1.0/24 in VRF TENANT-A"]
classDef leaf fill:#1b5e20,stroke:#81c784,color:#ffffff,stroke-width:2px,font-weight:bold;
classDef spine fill:#0d47a1,stroke:#64b5f6,color:#ffffff,stroke-width:2px,font-weight:bold;
class Leaf1,Leaf2 leaf; class SpineRR spine;4. Route Types 1 & 4 · ESI All-Active Multihoming¶
- Route Type 4 (Ethernet Segment): VTEPs connected to the same multi-homed server exchange Type 4 routes to discover each other and elect a Designated Forwarder (DF) for BUM traffic.
- Route Type 1 (Ethernet Auto-Discovery): Advertises ESI Split Horizon labels and enables Fast Failover (Mass Withdraw). If a link to a multi-homed server fails, the leaf sends a single Type 1 withdraw, instantly diverting traffic to the redundant leaf in < 50\,\text{ms}!