High availability technologies, Fault detection technologies – H3C Technologies H3C S12500 Series Switches User Manual
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MTTR = fault detection time + hardware replacement time + system initialization time + link recovery time
+ routing time + forwarding recovery time. A smaller value of each item means a smaller MTTR and a
higher availability.
High availability technologies
As previously mentioned, increasing MTBF or decreasing MTTR can enhance the availability of a
network. The high availability technologies described in this section meet the level 3 high availability
requirements in the aspect of 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. DLDP and Ethernet OAM
are data link layer fault detection technologies; BFD is a generic fault detection technology that can be
used at any layer; 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
Technology 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.
DLDP
The Device link detection protocol (DLDP) deals with unidirectional
links that might occur in a network. On detecting a unidirectional link,
DLDP, as configured, can shut down the related port automatically or
prompt users to take actions to avoid network problems.
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.
BFD
Bidirectional forwarding detection (BFD) provides a single mechanism
to quickly detect and monitor the connectivity of links or IP forwarding
in networks. To improve network performance, devices must quickly
detect communication failures to restore communication through
backup paths as soon as possible.
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.
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.