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Configuration Guide - Reliability

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

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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Typically, Intermediate System to Intermediate System (IS-IS) sends Hello packets at an interval of 10s. The holdtime of neighbors is three times the interval at which Hello packets are sent. If the switch does not receive a Hello packet from its neighbor within the holdtime, the switch deletes the neighbor relationship. This means that the switch detects neighbor faults after several seconds, which leads to significant packet loss on a high-speed network.

In BFD for IS-IS, BFD session establishment is triggered dynamically by IS-IS and is not configured manually. When detecting a fault, the BFD session notifies IS-IS through the RM. IS-IS will then:
  • Process the neighbor Down event.
  • Quickly update the link state PDU (LSP).
  • Perform partial route calculation (PRC).

This speeds up IS-IS route convergence. BFD does not replace the Hello mechanism of IS-IS, but instead works with IS-IS to quickly detect link faults and to immediately notify IS-IS of route recalculation, guiding packet forwarding. Table 2-2 lists IS-IS convergence time.

Table 2-2 IS-IS convergence time

BFD Session

Link Fault Detection Mechanism

Convergence Time

Not bound

Hello mechanism

Measured in seconds


BFD session in Down state

Measured in milliseconds


Figure 2-7 BFD for IS-IS

In Figure 2-7, IS-IS is enabled on all the devices and an association between BFD and IS-IS is enabled on SwitchA and SwitchB. When the link between SwitchA and SwitchB fails, BFD can quickly detect the fault and report the fault to IS-IS. IS-IS then disconnects the neighbors of this interface, which triggers topology calculation. IS-IS updates LSPs so that the neighbors, for example, Switch B's neighbor SwitchC, can receive the updated LSPs from SwitchB. This implements fast convergence when running IS-IS.

Updated: 2019-04-03

Document ID: EDOC1100075366

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