2
High availability technologies
Increasing MTBF or decreasing MTTR can enhance the availability of a network. The high availability
technologies described in this section meet the level 2 and level 3 high availability requirements by
decreasing MTTR.
High availability technologies can be classified as fault detection technologies or protection switchover
technologies.
Fault detection technologies
Fault detection technologies enable detection and diagnosis of network faults. CFD, DLDP, and Ethernet
OAM are data link layer fault detection technologies. NQA is used for diagnosis and evaluation of
network quality. Monitor Link and Track work along with other high availability technologies to detect
faults through a collaboration mechanism.
Table 2 Fault detection technologies
Technolo
Introduction Reference
CFD
Connectivity Fault Detection (CFD), which conforms to IEEE
802.1ag Connectivity Fault Management (CFM) and ITU-T
Y.1731, is an end-to-end per-VLAN link layer Operations,
Administration and Maintenance (OAM) mechanism used for
link connectivity detection, fault verification, and fault
location.
"Configuring CFD" in High
Availability Configuration
Guide
DLDP
The Device link detection protocol (DLDP) deals with
unidirectional links that may occur in a network. Upon
detecting a unidirectional link, DLDP, as configured, can shut
down the related port automatically or prompt users to take
actions to avoid network problems.
"Configuring DLDP" in
High Availability
Configuration Guide
Ethernet OAM
As a tool monitoring Layer 2 link status, Ethernet OAM is
mainly used to address common link-related issues on the "last
mile". You can monitor the status of the point-to-point link
between two directly connected devices by enabling Ethernet
OAM on them.
"Configuring Ethernet
OAM" in High Availability
Configuration Guide
NQA
Network Quality Analyzer (NQA) analyzes network
performance, services and service quality through sending test
packets, and provides you with network performance and
service quality parameters such as jitter, TCP connection
delay, FTP connection delay and file transfer rate.
"Configuring NQA" in
Network Management
and Monitoring
Configuration Guide
Monitor Link
Monitor Link works together with Layer 2 topology protocols to
adapt the up/down state of a downlink port to the state of an
uplink port. This feature enables fast link switchover on a
downstream device in response to the uplink state change on
its upstream device.
"Configuring Monitor Link"
in High Availability
Configuration Guide
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