EVPN Features in EVPNs using EVPN LAGs
This section introduces some commonly-used features in EVPNs that are using EVPN LAGs.
EVPN aliasing is the ability of a remote device to load balance Layer 2 unicast traffic across an Ethernet segment towards an endpoint device. See the Aliasing section of the EVPN Multihoming Overview topic for additional information on aliasing.
Servers and BladeCenter switches connected to an EVPN LAG with multiple links may send ARP requests to one of the leaf devices. The leaf devices respond by advertising the MAC address to the rest of the EVPN topology using the overlay iBGP peerings. The other leaf devices in the EVPN network use the default EVPN aliasing (EVPN Route type 1 per EVI) functionality to learn the EVPN Type 2 MAC routes from other leaf devices. All of the leaf devices are connected to the same ESI, however, for forwarding purposes.
EVPN LAG Multihomed Proxy Advertisement
A leaf device in a network running EVPN responds to a server’s ARP request with a MAC and IP EVPN Type 2 route.
Starting in Junos OS Release 18.4, multiple leaf devices that have links in the same EVPN LAG have the capability of also advertising MAC and IP EVPN Type 2 routes to the server that sent the ARP request. This capability is possible using the proxy M-bit in EVPN Type 2 routes. This capability is especially beneficial in failure scenarios. If a switch is multihomed to two leaf devices and the link to one of those devices fails, a Type 2 message can be sent toward the server that initially sent the ARP request and traffic can be sent across the network over the active links.
High Availability in EVPN LAGs
EVPN LAGs include many built-in high availability capabilities.
EVPN LAG link level fast convergence is delivered using the EVPN IBGP route type I massive withdrawal message. Node level fast convergence is handled using the BFD for IBGP in the overlay network. Node-level Layer 2 EVPN LAG redundancy is available in an EVPN-VXLAN fabric using built-in EVPN loop prevention mechanisms like split horizon and designated forwarding. Spanning tree protocol (STP) does not need to run in an EVPN-VXLAN fabric. See Designated Forwarding Election and Split Horizon in the EVPN Multihoming Overview topic for additional information on these features.
The core isolation feature quickly brings down the local EVPN-LAG when all IBGP EVPN overlay peerings are lost. This feature diverts traffic to other paths when a link is down. See When to Use the Core Isolation Feature for additional information on core isolation.
EVPN LAG Interfaces Advanced Capabilities
EVPN LAG multihoming has a series of advanced feature capabilities when compared to other LAG multihoming technologies such as Virtual Chassis or Multichassis link aggregation (MC-LAG). The advanced features include Proxy ARP and ARP suppression, IGMP proxy, MAC mobility, MAC history, and duplicate MAC detection.
ARP suppression in an ERB architecture helps reduce Ethernet broadcast traffic flooding across the Layer 2 fabric, thereby freeing up server resources across the fabric. ARP requests, therefore, are not flooded to other leaf devices when the ARP table is already populated with the address from other signaling events, most notably EVPN route sharing. See EVPN Proxy ARP and ARP Suppression, and NDP and NDP Suppression for additional information on Proxy ARP and ARP suppression.
IGMP proxy helps reduce IGMP membership report flooding in a data center by translating the IGMP messages into EVPN type 6 routes to send to all of the leaf devices in the data center. See Overview of IGMP Snooping in an EVPN-VXLAN Environment for additional information on IGMP Proxy. MAC mobility history allows EVPN LAGs to track how often a MAC address moves between ESIs. MAC mobility history allows network administrators to create security actions based on MAC address movements while also simplifying MAC address-related administration in an EVPN. See Overview of MAC Mobility for additional information on this feature.