Huawei Quidway NetEngine80E Configuration Manual page 528

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
BFD for IS-IS
The NE80E/40E supports BFD for IS-IS to detect IS-IS neighbor relationships. BFD can fast
detect the faults on links between IS-IS neighbors and reports them to IS-IS. Fast convergence
of IS-IS is then implemented.
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Issue 02 (2014-09-30)
An IS-IS network running normally is stable. The network seldom changes frequently, and
an IS-IS device does not calculate routes frequently. Therefore, you can set a short interval
(in milliseconds) for triggering the route calculation for the first time. If the network
topology changes frequently, the value of the intelligent timer increases with the calculation
times, and the interval for route calculation becomes longer. This prevents excessive CPU
resource consumption.
The LSP generation intelligent timer is similar to the SPF intelligent timer. In IS-IS, when
the LSP generation timer expires, the system regenerates its own LSP according to the
current topology. In the original implementation mechanism, a timer with a fixed value is
used, which, however, cannot meet the requirements on fast convergence and low CPU
usage. Therefore, the LSP generation timer is designed as an intelligent timer so that it can
respond quickly to some emergent events (such as interface alternation between Up and
Down) to speed up network convergence. In addition, when the network changes
frequently, the value of the intelligent timer becomes greater automatically to prevent
excessive CPU resource consumption.
NOTE
Determine whether to configure intelligent timers based on actual network situations and
specifications of deployed routers.
NOTE
BFD detects only one-hop links between IS-IS neighbors. This is because IS-IS establishes only one-hop
neighbors.
Static BFD
To configure static BFD, use command lines to configure single-hop BFD parameters, such
as local and remote discriminators. Then configure the device to send BFD session setup
requests.
A static BFD session can only be established and released manually. A configuration error
will lead to a BFD failure. For example, if the configured local discriminator or remote
discriminator is incorrect, a BFD session will not work properly.
The NE80E/40E supports static IPv4 BFD for IS-IS.
Dynamic BFD
Dynamic BFD refers to the dynamic establishment of BFD sessions using routing protocols.
When a new IS-IS neighbor relationship is set up, BFD is notified of the parameters of the
neighbor and the detection parameters (including source and destination IP addresses).
Then a BFD session will be established based on the received parameters of the neighbor.
Dynamic BFD is more flexible than static BFD.
Connection status between an IS-IS device and its neighbors can be monitored by
exchanging Hello packets at intervals. The sending interval is usually set to 10s, and a
neighbor is declared Down after at least three intervals (during which no response Hello
packet is received from the neighbor). It takes IS-IS some seconds to sense a Down
neighbor, resulting in loss of a large amount of high-speed data.
Dynamic BFD can provide link failure detection with light load and high speed (at the
millisecond level). Dynamic BFD does not take the place of the Hello mechanism of IS-
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