Explains EVPN fundamentals by defining Ethernet Segments, EVPN instances, route types, and operational modes essential to Ethernet VPNs.
Here are the key concepts related to EVPN fundamentals, including Ethernet Segments, EVPN instances, and associated mechanisms for traffic management and redundancy:
-
Ethernet segment (ES)—is a set of Ethernet links that connects a multihomed device or network to two or more PEs, and uses Ethernet segment route (route type 4) for designated forwarder (DF) election for BUM traffic.
-
Ethernet segment identifiers (ESI)—are unique non-zero identifiers that are assigned to Ethernet segments, and represent each Ethernet segment uniquely across the network.
-
EVPN instances (EVI)—is a virtual network identifier (VNI) on a PE router that acts like a VPN Routing and Forwarding (VRF), uses Route Targets (RTs) for import and export policies, maps traffic from ports or VLANs to a Bridge Domain (BD), and forwards it to the MPLS core.
-
Ethernet auto discovery routes per ES (EAD-ES)—is also referred to as route type 1 that is used to converge traffic faster during access failure scenarios, and has an Ethernet Tag of 0xFFFFFFFF.
-
Ethernet auto discovery routes per EVI (EAD-EVI)— is also referred to as route type 1 that is used for aliasing and load balancing when traffic only hashes to one of the switches, and cannot have an Ethernet tag value of 0xFFFFFFFF to differentiate it from the EAD-ES route.
-
Aliasing—is a process that is used for load balancing traffic to all connected switches for a given Ethernet segment using the route type 1 EAD-EVI route, and is performed irrespective of the switch where the hosts are actually learned.
-
Mass withdrawal—is a process that is used for fast convergence during access failure scenarios using the route type 1 EAD-ES route.
-
DF election—is a process that is used to prevent forwarding loops, and allows only a single router to decapsulate and forward traffic for a given Ethernet Segment.
-
VPN membership—is the process where PEs exchange EVPN routes at startup to discover remote PE members of an EVI, which enables building flood lists for multicast ingress replication and exchanging BUM and unicast labels for MAC address learning.
-
Ethernet segment reachability—is a process where, in multihoming scenarios, the PE auto-discovers remote PE and the corresponding redundancy mode (all-active or single-active), which allows PEs to withdraw the routes used at this stage in case of segment failures in order to trigger fast convergence by signaling a MAC mass withdrawal on remote PEs.
-
Redundancy group membership—is a process where PEs connected to the same Ethernet segment (multihoming) automatically discover each other and elect a Designated Forwarder (DF) that is responsible for forwarding Broadcast, Unknown unicast, and Multicast (BUM) traffic for a given EVI.
EVPN route types
EVPN supports EVPN route types that define several route types that serve different purposes in delivering Layer 2 and Layer 3 services over an IP-MPLS network. Each route type carries specific information.
| Route Type |
Description |
Usage |
|---|---|---|
| Route Type 1: Ethernet Auto-Discovery (AD) Route |
The Ethernet Auto-Discovery (AD) routes are advertised on per EVI and per ESI basis. These routes are sent per ES. They carry the list of EVIs that belong to the ES. The ESI field is set to zero when a CE is single-homed. This route type is used for mass withdrawal of MAC addresses and aliasing for load balancing. |
Few routes are sent per ES, carries the list of EVIs that belong to ES. |
Route Type 2: MAC-IP Advertisement Route |
These routes are per-VLAN routes, so only PEs that are part of a VNI require these routes. The host's IP and MAC addresses are advertised to the peers within NRLI. The control plane learning of MAC addresses reduces unknown unicast flooding. |
Advertises MAC address reachability and IP-MAC binding. |
| Route Type 3: Inclusive Multicast Ethernet Tag Route |
This route establishes the connection for broadcast, unknown unicast, and multicast (BUM) traffic from a source PE to a remote PE. This route is advertised on per VLAN and per ESI basis. |
Discovers multicast tunnel end point. |
| Route Type 4: Ethernet Segment Route |
Ethernet segment routes enable to connect a CE device to two or PE devices. ES route enables the discovery of connected PE devices that are connected to the same Ethernet Segment. |
Discovers redundancy group and DF election. |
| Route Type 5: IP Prefix Route |
The IP prefixes are advertised independently of the MAC-advertised routes. With EVPN IRB, host route /32 is advertised using RT-2 and subnet /24 is advertised using RT-5. |
Advertises IP prefixes. |
With EVPN IRB, host route /32 are advertised using RT-2 and subnet /24 are advertised using RT-5.
EVPN modes
EVPN modes address modern network needs like scalability, multi-tenancy, redundancy, and workload mobility, providing a unified solution for Layer 2 and Layer 3 services. These modes provide an efficient solution for Layer 2 and Layer 3 services, ensuring operational simplicity, high performance, and flexibility for data centers, service providers, and cloud environments.
These EVPN modes are supported:
-
Single-homing—enables you to connect a customer edge (CE) device to one provider edge (PE) device.
-
Multihoming—enables you to connect a customer edge (CE) device to more than one provider edge (PE) device. Multihoming ensures redundant connectivity, so that there is no traffic disruption when there is a network failure. These multihoming modes are supported:
-
All-active
-
Single-active
-
Single-flow active
-
Port-active
-