EVPN EPL Link-Loss Forwarding

OcNOS SP : Multi-Protocol Label Switching Guide : Multi-Protocol Label Switching Configuration : EVPN EPL Link-Loss Forwarding

Overview

Link Loss Forwarding (LLF) is a fault propagation feature for EVPN Ethernet Private Line (EPL) services that ensures reliable point-to-point connections on physical interfaces. It prevents traffic blackholing by detecting remote service failures and bringing the local physical link operationally down, enabling the local end to trigger a traffic failover mechanism. LLF is supported on all Broadcom chipsets and uses Ethernet Auto-Discovery (AD) per EVI (RT-1) route withdrawal for fault propagation, which is enabled by default.

The feature can be configured per service using the CLI command llf enable in interface mode. By facilitating proactive fault handling, LLF ensures minimal downtime, improves service reliability, and enhances traffic management for customers relying on point-to-point connections.

Feature Characteristics

Link Loss Forwarding (LLF) enhances the reliability of EVPN Ethernet Private Line (EPL) connections by detecting remote failures, bringing the local link down to initiate failover, and preventing traffic blackholing. It ensures prompt communication of service interruptions to minimize downtime and prevent data loss.

Benefits

LLF enhances networking environments by ensuring minimal service downtime, reliable traffic failover, and increased network stability.

• Minimized Service Downtime: Quick detection and propagation of faults reduce recovery time.

• Traffic Failover Assurance: Reliable failover mechanisms are enabled, ensuring minimal impact on customer services.

• Improved Network Reliability: The proactive nature of LLF enhances the robustness of EVPN EPL services.

Configuration of LLF for an EVPN Ethernet Private Line (EPL)

To configure LLF on an interface, follow the below steps to ensure that network faults are managed effectively, preventing traffic loss or blackholing by administratively adjusting the status of affected interfaces based on the fault condition.

Topology

The topology consists of two Customer Edge devices (CE1 and CE2) connected to Provider Edge devices (PE1 and PE2) through sub-interfaces. The Provider Edge devices are interconnected through MPLS. In this topology, the Link Loss Forwarding (LLF) configuration for an EVPN Ethernet Private Line (EPL) service ensures fault propagation to prevent traffic blackholing during link failures. When a link failure occurs, such as between CE-1 and PE-1 on interface xe1.1, PE-1 detects the issue and withdraws the Ethernet Auto-Discovery (AD) per EVI (RT-1) route. This withdrawal is propagated through the MPLS network to PE-2, which then takes action to bring down the corresponding physical interface (xe22.2). This mechanism ensures the fault is communicated end-to-end, allowing CE-2 to detect the failure and trigger failover mechanisms. LLF is enabled through the LLF enable command at the interface level, ensuring automated fault detection and seamless service continuity.

Link-loss Forwarding Topology

Configuration XE22.2

Follow these steps to configure LLF on PE2.

1. Access the interface configuration mode, configure the interface xe22.2. Set the interface as a switch port.

PE2(config)#configure terminal

PE2(config)#int xe22.2 sw

2. Specify the encapsulation type as dot1q and set the VLAN ID to 10. Enable the interface to support EVPN services.

PE2(config-if)#encapsulation dot1q 10

PE2(config-if)#access-if-evpn

3. Enable LLF on the interface to ensure link failure detection and recovery. Save the changes and exit the configuration mode.

PE2(config-acc-if-evpn)#llf-enable

PE2(config)#commit

PE2(config)#exit

Validation

To validate the proper configuration of Link Loss Forwarding (LLF), use the show running-config interface xe22.2 command to inspect the interface settings. Ensure that the interface is configured with switchport, encapsulation dot1q 10 for VLAN tagging, access-if-evpn to enable EVPN on the interface, llf-enable to activate LLF, and map vpn-id 10 to associate the service with the correct VPN ID. Verify that these attributes are present and correctly configured. If discrepancies are found, update the configuration and recheck to ensure the LLF setup is correct and operational.

#show running-config interface xe22.2

interface xe22.2 switchport

encapsulation dot1q 10

access-if-evpn

llf-enable

map vpn-id 10

Rvtep#sh evpn mpls llf-status

status : is_up\is_running

ifp-name sub-Ifname llf-configured RT-1-rcvd llf-action

______________________________________________________________________________

xe16 (DOWN\---) xe16.2 (UP\---) YES NO YES

Total number of entries are 1

Rvtep#sh int brief

xe16.2 SUBINTERFACE -- -- down PD 10g -- No No

Rvtep#sh int xe16

Interface xe16

Flexport: Non Control Port (Active)

Hardware is ETH Current HW addr: e8c5.7a8f.c60e

Physical:e8c5.7a8f.c60e Logical:(not set)

Forward Error Correction (FEC) configured is Auto (default)

FEC status is N/A

Port Mode is Router

Protected Mode is Promiscuous

Interface index: 10037

GMPLS index: 39

Metric 1 mtu 1500 duplex-full link-speed 10g

Debounce timer: disable

ARP ageing timeout 1500

<BROADCAST,MULTICAST>

Reason: LLF DOWN

VRF Binding: Not bound

Label switching is disabled

No Virtual Circuit configured

Administrative Group(s): None

Regular Extended-Admin-Group(s): None

Anomaly Extended-Admin-Group(s): None

Bandwidth 10g

Maximum reservable bandwidth 10g

Available b/w at priority 0 is 10g

Available b/w at priority 1 is 10g

Available b/w at priority 2 is 10g

Available b/w at priority 3 is 10g

Available b/w at priority 4 is 10g

Available b/w at priority 5 is 10g

Available b/w at priority 6 is 10g

Available b/w at priority 7 is 10g

DHCP client is disabled.

Last Flapped: 2024 Oct 25 21:46:12 (00:00:44 ago)

Load Interval: 30 seconds.

Statistics last cleared: Never

inet6 fe80::eac5:7aff:fe8f:c60e/64

ND router advertisements are sent approximately every 442 seconds

ND next router advertisement due in 0 seconds.

ND router advertisements live for 1800 seconds

Hosts use stateless autoconfig for addresses.

unicast packets 0 multicast packets 0 broadcast packets 0

input packets 0 bytes 0

jumbo packets 0

undersize 0 oversize 0 CRC 0 fragments 0 jabbers 0

input error 0

input with dribble 0 input discard 0

Rx pause 0

unicast packets 0 multicast packets 10 broadcast packets 0

output packets 10 bytes 1020

jumbo packets 0

output errors 0 collision 0 deferred 0 late collision 0

output discard 0

Tx pause 0

Rvtep#

New CLI Commands

The llf introduces the following configuration commands in OcNOS.

llf-enable

Use this command to enable the link-loss forwarding on an access-interface.

Use the no parameter to disable the load interval globally.

Command Syntax

llf-enable

no llf-enable

Parameters

None

Default

Disabled

Command Mode

Access-if mode

Applicability

Introduced in OcNOS version 6.6.0.

Example

The following example illustrates how to activate EVPN Ethernet Private Line (EPL).

#configure terminal

(config)#int xe22.2 sw

(config-if)#encapsulation dot1q 10

(config-if)#access-if-evpn

(config-acc-if-evpn)#llf-enable

Glossary

The following provides definitions for key terms or abbreviations and their meanings used throughout this document:


Key Terms/Acronym	Description
LLF	Link Loss Forwarding (LLF) is a feature in networking, particularly in Ethernet-based networks like Ethernet Virtual Private Network (EVPN), that is designed to prevent traffic blackholing during link failures.
EPL	Ethernet Private Line (EPL) is a high-performance, point-to-point Ethernet service used for dedicated connectivity between two locations.
MPLS	Multiprotocol Label Switching (MPLS) is a high-performance routing technique used in modern telecommunications networks to efficiently route data packets.