Evpn Single-Homing Access Evpn Gateway; Evpn Multi-Homing Active-Active - Cisco ASR 9000 Series Configuration Manuallines

EVPN Single-Homing Access EVPN Gateway

The above figure illustrates a scenario where EVPN IRB is deployed using three EVPN PE routers that provide
single-homing or multi-homing Active-Active access. The PE routers exchange EVPN and IP VPN BGP
address-families information. In Cisco ASR 9000 Series Aggregation Services Router, the centralized EVPN
gateway with both EVPN and VPN address-families are enabled, so EVPN route stitching and re-origination
does not occur. The single IP VPN gateway provides access to other IP VPNs or the Internet. The IP VPN
gateway exchanges VPNv4 or VPNv6 address families with the EVPN PE routers but EVPN address family
is not available.
In the above figure, the host sends an IP packet whose frame contain its MAC and IP address. The frame of
the packet also includes the destination MAC address of the BVI interface of the local PE device and the IP
address of the destination host. When the host is required to send packets for routing to other subnets and IP
VPN or the Internet, the host uses the MAC address of the local BVI interface as destination MAC address.
The IRB interface receives the packet in whose frame the interface's MAC address is set as the destination.
The IRB interface routes the packet to the destination after looking up the VRF table. The PE device chooses
an intra-subnet route registered earlier in the VRF table. The MAC address that matches the destination IP,
in the earlier route, becomes the new MAC address which replaces the existing MAC address in the packet.
The packet reaches the destination remote PE device, to which the destination host is connected, which does
an inter-subnet looks up in the VRF table for the MAC address of the destination host. Then, through the IRB
interface, the remote PE device forwards the packet to the destination host.
EVPN Single-Homing Access EVPN Gateway
The EVPN provider edge (PE) devices learn the MAC address and IP address from the ARP traffic that they
receives from the customer edge (CE) devices. The PEs create the MAC+IP routes. The PEs advertise the
MAC+IP routes to MPLS core. They inject the host IP routes to IP-VPN gateway. All the PE nodes add the
host routes in the IP-VRF table. The EVPN PE nodes add MAC route to the MAC-VRF table. The IP-VPN
PE advertise the subnet routes to the provider edge devices who add the subnet routes to IP-VRF table. On
the PE devices, IRB IP addresses and MAC addresses are not advertised through BGP. The IRB IP addresses
or MAC addresses are used to send ARP requests towards the datacenter CEs.

EVPN Multi-Homing Active-Active

EVPN Multi-homing access gateway enables redundant network connectivity by allowing a CE device to
connect to more than one PE devices. Disruptions to the network connectivity are prevented by allowing a
CE device to be connected to a PE device or several PE devices through multi-homing. Ethernet segment is
the bunch of Ethernet links through which a CE device is connected to more than one PE devices. The
Multi-chassis Link Aggregation Group (MC-LAG) bundle operates as an Ethernet segment. In Release 6.2.1,
only MC bundles crossing two chassis are supported.
In EVPN IRB, both EVPN and IP VPN (both VPNv4 and VPNv6) address families are enabled between ASR
9000 Data Center Interconnect (DCI) gateways. When Layer 2 (L2) stretch is not available in multiple
datacenters (DC), routing is established through VPNv4 or VPNv6 routes. When Layer 2 stretch is available,
host routing is applied where IP-MAC routes are learnt by ARP/IPv6 ND and are distributed to EVPN/BGP.
In remote peer gateway, these IP-MAC EVPN routes are imported into IP VPN routing table from EVPN
route-type 2 routes with secondary label and Layer 3 VRF route-target.
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
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Configure EVPN IRB