Today, our networks have different protocols serving different purposes, which makes daily operations more complex than they need to be. This hinders the ability to deliver end-to-end services with speed and agility. As you deploy multiple geographically disparate data centers, they're looking for scalable and simplified network solutions to extend virtualization and cluster domains between multiple data centers.

Ethernet VPN (EVPN) is the next-generation L2VPN technology, and it provides layer 2 and 3 VPN services in a scalable and simplified manner. The evolution of EVPN started due to the need for a scalable solution to bridge various layer 2 domains and overcome the limitations faced by VPLS, such as scalability, multihoming, and per-flow load balancing.

EVPN provides secure and private connectivity of multiple sites within an organization spread across different geographical locations. EVPN operates in contrast to the existing VPLS by enabling control-plane-based MAC learning. In EVPN, PEs participating in the EVPN instances learn customer MAC routes in the control plane using the MP-BGP protocol. EVPN brings various benefits addressing the VPLS shortcomings, including multi-homing support with per-flow load balancing. EVPN uses MAC addresses as routable addresses and distributes them to all participating PEs through the MP-BGP EVPN control plane.

To know more about EVPN, visit https://e-vpn.io.

EVPN supports E-LAN, E-LINE, E-TREE services, and provides data-plane and control-plane separation, and much more.

EVPN allows the use of different encapsulation mechanisms in the data plane while maintaining the same control plane. In addition, EVPN offers many advantages over existing technologies, including more efficient load-balancing of VPN traffic.

To implement EVPN features, you need to understand the following concepts:

• Ethernet Segment (ES): An Ethernet segment is a set of Ethernet links that connects a multihomed device. If a multi-homed device or network is connected to two or more PEs through a set of Ethernet links, then that set of links is referred to as an Ethernet segment. The Ethernet segment route is also referred to as Route Type 4. This route is used for designated forwarder (DF) election for BUM traffic.

• Ethernet Segment Identifier (ESI): Ethernet segments are assigned a unique non-zero identifier, which is called an Ethernet Segment Identifier (ESI). ESI represents each Ethernet segment uniquely across the network.

• EVI: The EVPN instance (EVI) is represented by the virtual network identifier (VNI). An EVI represents a VPN on a PE router. It serves the same role of an IP VPN Routing and Forwarding (VRF), and EVIs are assigned import/export Route Targets (RTs). Depending on the service multiplexing behaviors at the User to Network Interface (UNI), all traffic on a port (all-to-one bundling), or traffic on a VLAN (one-to-one mapping), or traffic on a list/range of VLANs (selective bundling) can be mapped to a Bridge Domain (BD). This BD is then associated to an EVI for forwarding towards the MPLS core.

• EAD/ES: Ethernet Auto Discovery Route per ES is also referred to as Route Type 1. This route is used to converge the traffic faster during access failure scenarios. This route has Ethernet Tag of 0xFFFFFFFF.

• EAD/EVI: Ethernet Auto Discovery Route per EVI is also referred to as Route Type 1. This route is used for aliasing and load balancing when the traffic only hashes to one of the switches. This route cannot have Ethernet tag value of 0xFFFFFFFF to differentiate it from the EAD/ES route.

• Aliasing: It is used for load balancing the traffic to all the connected switches for a given Ethernet segment using the Route Type 1 EAD/EVI route. This is done irrespective of the switch where the hosts are actually learned.

• Mass Withdrawal: It is used for fast convergence during the access failure scenarios using the Route Type 1 EAD/ES route.

• DF Election: It is used to prevent forwarding of the loops. Only a single router is allowed to decapsulate and forward the traffic for a given Ethernet Segment.

At startup, PEs exchange EVPN routes in order to advertise the following:

• VPN membership: The PE discovers all remote PE members of a given EVI. In the case of a multicast ingress replication model, this information is used to build the PEs flood list associated with an EVI. BUM labels and unicast labels are exchanged when MAC addresses are learned.

• Ethernet segment reachability: In multihoming scenarios, the PE auto-discovers remote PE and the corresponding redundancy mode (all-active or single-active). In case of segment failures, PEs withdraw the routes used at this stage in order to trigger fast convergence by signaling a MAC mass withdrawal on remote PEs.

• Redundancy Group membership: 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 can operate in single-homing or dual-homing mode. Consider single-homing scenario, when EVPN is enabled on PE, Route Type 3 is advertised where each PE discovers all other member PEs for a given EVPN instance. When an unknown unicast (or BUM) MAC is received on the PE, it is advertised as EVPN Route Type 2 to other PEs. MAC routes are advertised to the other PEs using EVPN Route Type 2. In multihoming scenarios, Route Types 1, 3, and 4 are advertised to discover other PEs and their redundancy modes (single-active or all-active). Use of Route Type 1 is to auto-discover other PE which hosts the same CE. The other use of this route type is to fast route unicast traffic away from a broken link between CE and PE. Route Type 4 is used for electing designated forwarder. For instance, consider the topology when customer traffic arrives at the PE, EVPN MAC advertisement routes distribute reachability information over the core for each customer MAC address learned on local Ethernet segments. Each EVPN MAC route announces the customer MAC address and the Ethernet segment associated with the port where the MAC was learned from and its associated MPLS label. This EVPN MPLS label is used later by remote PEs when sending traffic destined to the advertised MAC address.

The EVPN network layer reachability information (NLRI) provides different route types.

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.

Note	With EVPN IRB, host route /32 are advertised using RT-2 and subnet /24 are advertised using RT-5.

The following EVPN modes are supported:

• Single-homing - Enables you to connect a customer edge (CE) device to one provider edge (PE) device.

The following table shows various EVPN timers:

Note

The timers are available in EVPN global configuration mode and in EVPN interface sub-configuration mode. Startup-cost-in is available in EVPN global configuration mode only. Timers are triggered in sequence (if applicable). Cost-out in EVPN global configuration mode brings down AC link(s) to prepare node for reload or software upgrade.

^* indicates all required software components are loaded.

^** indicates link status is up.

^*** you can change the recovery timer on Single-Homed AC if you do not expect any STP protocol convergence on connected CE.