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Configuration Guide - Reliability

CloudEngine 12800 and 12800E V200R002C50

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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Association Between VRRP and BFD to Implement a Rapid Active/Standby Switchover

Association Between VRRP and BFD to Implement a Rapid Active/Standby Switchover

A VRRP group sends and receives VRRP Advertisement packets to determine the master and backup states, thereby implementing redundancy. When a VRRP group is faulty, the backup with the highest priority detects the fault and switches to the master after the Master_Down_Interval timer expires. The switchover period is at least 3s. During this switchover period, service traffic is still sent to the original master, causing loss of user traffic. Association between VRRP and BFD prevents traffic loss. After a BFD session is configured between the master and the backup, and the BFD session is bound to the VRRP group, the BFD session detects connectivity of the VRRP group. When detecting a fault, the BFD session instructs the VRRP group to perform an active/standby switchover. This mechanism implements switchover in milliseconds and reduces traffic loss.

Table 3-3 describes the association between the VRRP group and BFD session.

Table 3-3 VRRP and BFD association modes

Association Mode

BFD Session Type

Usage Scenario

VRRP Status Change

Association between a VRRP group and a common BFD session

Static BFD session or static BFD session with automatically negotiated discriminators

A backup monitors the status of the master in a VRRP group. A common BFD session monitors the link between the master and backup.

If the BFD session detects a fault and goes Down, the BFD module notifies the VRRP group of the status change. When receiving the notification, the VRRP group changes VRRP priorities of devices and determines whether to perform an active/standby switchover.

Association between a VRRP group and a link/peer BFD session

Static BFD session or static BFD session with automatically negotiated discriminators

The master and backup monitor the link/peer BFD session. A link BFD session is established between the master and backup. A peer BFD session is established between a downstream switch and each VRRP device. The BFD module helps the VRRP group detect faults on a link between a VRRP-enabled device and the downstream switch.

If the link/peer BFD session detects a fault and goes Down, the BFD module notifies the VRRP group of the status change. After receiving the notification, the VRRP group rapidly performs an active/standby switchover.

Association between a VRRP group and a VRID-based dynamic BFD session

VRID-based dynamic BFD session

A backup monitors the status of the master in a VRRP group. A VRID-based dynamic BFD session is used to monitor the link between the master and backup.

If the VRID-based dynamic BFD session goes Down, the BFD module notifies the VRRP group of the fault. After receiving the notification, the VRRP group immediately performs an active/standby switchover without changing the VRRP priorities.

Figure 3-10 Association between a VRRP group and a common BFD session

In Figure 3-10, a VRRP group is configured between SwitchA and SwitchB, which are the master and backup, respectively. User traffic is forwarded through SwitchA. Delayed preemption is configured on SwitchA and immediate preemption is configured on SwitchB. BFD sessions are configured on SwitchA and SwitchB and association between VRRP and BFD is configured on SwitchB.

When a fault occurs in the VRRP group, BFD rapidly detects the fault and instructs SwitchB to increase the priority. In this case, SwitchB has a higher priority than SwitchA and therefore becomes the master and forwards user traffic. In this way, a rapid active/standby switchover is implemented.

Figure 3-11 Association between a VRRP group and a link/peer BFD session

In Figure 3-11, a VRRP group is configured between SwitchA and SwitchB, which are the master and backup, respectively. User traffic is forwarded through SwitchA. Delayed preemption is configured on SwitchA and immediate preemption is configured on SwitchB. A peer BFD session is established between SwitchA and SwitchB. Link1 BFD session is established between the switch and SwitchA. Link2 BFD session is established between the switch and SwitchB. Association between VRRP and BFD is configured on SwitchB.

When a fault occurs in the VRRP group, Link1 BFD session and the peer BFD session go Down. Link2 BFD session is Up. SwitchA's VRRP status directly becomes Initialize. SwitchB's VRRP status directly becomes the master and therefore forwards user traffic. In this way, a rapid active/standby switchover is implemented.

Figure 3-12 Association between a VRRP group and a VRID-based dynamic BFD session

In Figure 3-12, a VRRP group is configured between SwitchA and SwitchB, which are the master and backup, respectively. User traffic is forwarded through SwitchA. Delayed preemption is configured on SwitchA and immediate preemption is configured on SwitchB. A VRRP group is configured on SwitchA and SwitchB to monitor the VRID-based dynamic BFD session.

If BFD detects a fault, the VRID-based dynamic BFD session goes Down. After receiving the session Down event, SwitchB immediately switches to the master and sends gratuitous ARP packets to update MAC address entries on the switch.

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Updated: 2019-03-21

Document ID: EDOC1000166606

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