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Configuration Guide - Reliability

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

This document describes the configurations of Reliability, including BFD Configuration, VRRP Configuration, DLDP Configuration, Smart Link and Monitor Link Configuration, EFM Configuration, and CFM Configuration.
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BFD for Perlink

BFD for Perlink

Two devices are directly connected through an Eth-Trunk in a VLAN. If BFD for IP is bound to the VLANIF interface to detect the Eth-Trunk, BFD selects a link of a member interface of the Eth-Trunk as the detection path. If this link is faulty and other links are normal, the BFD session becomes Down. In this case, BFD may incorrectly report faults.

To solve this problem, BFD for Perlink is used to detect an Eth-Trunk. After BFD for Perlink is bound to a VLANIF interface, a management session is created. In addition, a dynamic unicast BFD sub-session is created for each member interface of the Eth-Trunk. The management session does not perform negotiation and detection. Instead, it is used to manage the sub-session status and report the sub-session status to the upper-layer applications. BFD sub-sessions perform negotiation and detection, and report their status to the management session. The management session becomes Down only when all sub-sessions go Down.

The device supports BFD for Perlink based on the BFD echo function. The following describes the working process of BFD for Perlink on the network shown in Figure 2-11.

Figure 2-11 Networking of BFD for Perlink

A Transparent Interconnection of Lots of Links (TRILL) network is deployed between RB1 and RB2. GW1 is directly connected to RB1, and an inter-card Eth-Trunk is deployed between GW1 and RB1; GW2 is directly connected to RB2, and an inter-card Eth-Trunk is deployed between GW2 and RB2. Inter-card Eth-Trunks on GW1 and GW2 join the same VLAN. BFD is required to detect faults on the link between GW1 and GW2. After BFD for Perlink is configured on GW1:
  1. On GW1, a BFD sub-session is created for each Eth-Trunk member link, and a BFD echo packet is constructed and sent out from a specified member interface. The BFD echo packet uses the IP address of the local VLANIF interface as the destination IP address, GW2's MAC address as the destination MAC address, and dynamically created local and remote discriminators.
  2. RB1 receives the BFD packet from the member interface and forwards it through the TRILL network.
  3. After receiving the BFD packet, RB2 selects a member link to forward it according to the hash algorithm.
  4. After receiving the BFD packet, GW2 finds that the destination IP address of the BFD packet is the IP address of the VLANIF interface on GW1. GW2 immediately loops back the BFD packet in the forwarding plane.
  5. After receiving the loopback packet, RB2 forwards it through the TRILL network.
  6. After the loopback packet returns RB1, RB1 also selects a member link according to the hash algorithm and sends it to GW1.

In the forwarding process, if member link 1 between GW1 and RB1 becomes faulty, sub-session 1 becomes Down, but sub-session 2 is still Up. Therefore, the management session is still Up, and BFD does not report faults incorrectly.

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Updated: 2019-05-08

Document ID: EDOC1100004359

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