EVPN Active-Standby
Overview
EVPN Multihoming is a mechanism that allows a host or customer edge (CE) device to be connected to multiple Provider Edge (PE) devices called Multihoming (MH) peers for redundancy and load balancing purposes. This provides high availability and resiliency to the network, ensuring continuous connectivity even in case of a PE device failure.
OcNOS support extends to a maximum of two MH peers.
Multihoming supports two kinds of redundancy, namely 1. All Active 2. Active-Standby.
Till now, OcNOS support All-Active (A-A) only. In OcNOS version 6.4.1, Port-Active mode is supported and in OcNOS version 6.4.2, Single-Active mode is supported in the context of Active-Standby redundancy.
Single-Active
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In this mode, traffic for a specific host or MAC address is handled by only one of the PE devices (MH peers) at a time. |
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The other PE devices remain in standby mode, ready to take over if the active PE fails. |
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The physical link state (either Physical port or LACP port) on the standby PE remains up, enabling a faster transition to the active role in the event of a failover. The CE devices use different interfaces, including LACP or physical connections, to connect to the Peer MH devices. |
Port-Active
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In this mode, traffic for a specific host or MAC address is handled by only one of the PE devices (MH peers) at a time. |
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Each MH peer connects through LACP with the same key as the CE devices (similar to A-A redundancy). |
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The physical link state (LACP port) on the standby PE is made down, effectively blocking traffic on those ports. |
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If a failover occurs, the standby PE must bring up its LACP ports to start forwarding traffic. |
IRB Active-Standby: Active-standby mode is also applicable to Integrated Routing and Bridging (IRB) for both L3VPN symmetric and asymmetric modes.
Feature Characteristics
Single-Active standby redundancy mechanisms support both ELAN and ELINE services.
Single-Active ELINE
ELINE refers to Ethernet Line services, where two PEs are cross-connected to each other over an Ethernet link.
In Single-Active ELINE, the primary objective is to achieve redundancy for hosts while also using the same link for data exchange until it fails, at which point it should switch to the secondary or standby link. Here's how it works:
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One of the PE devices (MH peers) acts as the “Active” for the Attachment Circuit (AC) associated with the host. This PE sends and receives traffic to and from the host. |
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The other PE acts as the "Standby” for the same AC and does not allow traffic to or from the host. |
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The standby PE, despite receiving BUM traffic from the Host device (which is unaware of the cross-connect), blocks this traffic at the standby PE itself, as it operates in a standby role for the AC. Conversely, the active PE allows the flow of traffic. |
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Remote Host Traffic: Traffic originating from remote hosts destined for the multihomed host is only sent to the active MH peer for the corresponding AC. This ensures that the cross connect is established only with the Active MH peer. |
Single-Active ELAN
ELAN stands for Ethernet LAN services, where a group of PEs are interconnected in a multipoint Ethernet network.
In Single-Active ELAN, similar to Single-Active ELINE, redundancy for hosts and data exchange over the primary link are priorities, but there are some specific differences for Ethernet LAN (ELAN) scenarios:
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One of the PE devices (MH peers) is designated as the "Active" for the AC associated with the host. This PE handles sending and receiving traffic to and from remote locations. |
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The other PE acts as the "Standby" role for the same AC. It receives BUM traffic from the host but blocks the traffic. Additionally, it refrains from learning MAC addresses and does not uplift Address Resolution Protocol/Neighbor Discovery (ARP/ND) packets. |
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Unicast traffic from the host will be directed to the active PE, which will then allow the traffic to be sent across the network. |
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Remote Host Unicast Traffic: Unicast traffic from remote hosts destined for the multihomed host is sent only to the active MH peer for the corresponding AC. This is because the MAC addresses of the host are learned only from the Active MH peer. |
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Remote Host BUM Traffic: BUM traffic, such as broadcast and multicast packets from the remote PE device, is replicated to both MH PEs. However, only the active PE, which is also designated as a forwarder, allows this traffic to reach the host. The standby PE, classified as a Non-Designated Forwarder, drops the egress traffic. |
Port-Active Ethernet LAN (ELAN) and Ethernet LINE (ELINE) are examples of port-active standby redundancy mechanisms.
Port-Active ELINE
Port-Active ELINE enables redundancy and optimized data exchange by designating an active port for traffic handling in multihomed network setups. Here's how it works:
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Active AC Link: Among the Multihomed (MH) peers, a designated PE is assigned as "Active" for the AC associated with the host. This PE manages bidirectional traffic to and from the host. In a port-active configuration, all hosts associated with the ESI link remain in the same state, as the Active and Standby status is determined per ESI link. |
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Standby AC Link: The AC link attached to the host, designated as "Standby," remains operationally down. It serves as a backup link for failover scenarios. |
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MH Host traffic: BUM and unicast traffic from the host are always directed towards the Active PE because the link towards the Active PE is operational UP. Conversely, the link towards the Standby PE from the host devices is operational DOWN. |
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Remote Host Traffic: Traffic originating from remote hosts and destined for the multihomed host is directed exclusively to the Active MH node that serves the corresponding AC. This ensures efficient traffic routing and intelligent cross-connection establishment. |
Port-Active ELAN
Port-Active ELAN enhances redundancy and efficient data exchange by designating an active port for traffic management in multihomed Ethernet LAN environments. Here's how it works:
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Active AC Link: Within the MH peers, one PE is identified as the "Active" entity for the AC. It manages traffic to and from remote locations efficiently. |
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Standby AC Link: Similar to Port-Active ELINE, the standby AC link attached to the host remains operationally down to ensure effective standby redundancy. |
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MH Host Traffic: In a port-active scenario, the standby link does not receive any traffic from the host. Only the active link manages incoming traffic from the host. The Active PE also learns and advertises host information to remote locations, including MAC addresses and ARP/ND details. |
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Remote Host Unicast Traffic: Unicast traffic from remote sources is directed exclusively to the Active MH PE that has advertised the host address, optimizing traffic flow. |
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Remote Host BUM Traffic: BUM traffic is replicated across all MH nodes. However, egress traffic for BUM packets occurs only from the Active PE. The standby PE drops the traffic since the AC links are operational DOWN. |
Benefits
The benefits of Single-Active and Port-Active include enhanced redundancy and fault tolerance for hosts and customer edge devices, efficient data exchange, minimized downtime, and improved network resiliency in multihomed Ethernet Line and Ethernet LAN environments. These mechanisms ensure uninterrupted connectivity and optimized traffic management, contributing to higher availability and improved user experience.
Prerequisites
Here are the prerequisites for configuring EVPN Multihoming:
Ensure EVPN Configuration: Make sure that the EVPN is configured already in the network as it is a requirement for EVPN Multihoming.
Configure Attachment Circuits (AC): Ensure that each CE device is appropriately linked to the PE devices through Attachment Circuits. These circuits must be configured correctly.
Set Up LACP Configuration: To use Link Aggregation Control Protocol (LACP) for multihoming, configure LACP appropriately on the relevant interfaces.
EVPN MPLS Global Configuration: To enable EVPN MPLS features, need to configure global settings, such as enabling EVPN MPLS, defining global VTEP IP addresses, enabling hardware profile filtering for multihoming, and activating EVPN MPLS multihoming functionality. These settings are essential for EVPN and MPLS operation.
Access Port Configuration: Depending on the network's redundancy plan (single-active or port-active), configure access ports, including parameters for load balancing, service carving preferences, and EVPN settings. These configurations are crucial for network access and connectivity in an EVPN environment.
These prerequisites ensure that the network is ready for the implementation of EVPN Multihoming, providing redundancy and load balancing for CE devices.
Configuration
Here are sample configurations for EVPN MPLS Active-Standby MultiHoming Configuration and EVPN SR Active-Standby Multi-Homing Configuration, including topology, configuration procedures, and corresponding validations.
For more information on the EVPN MPLS configurations, see the and EVPN MPLS IRB Configuration chapters in the Multi-Protocol Label Switching Guide.