Huawei Quidway S3700 Series Configuration Manual page 296

Quidway S3700 Series Ethernet Switches
Configuration Guide - Reliability
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When the two ends of a BFD session create discriminators in different modes:
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Single-Hop BFD
Single-hop BFD detects connectivity of the forwarding link between two directly connected
devices.
Between the two systems detected by the single-hop BFD session, only one BFD session can be
set up on a specified interface enabled with a specified data protocol. Therefore, each BFD
session is bound to an interface. On the S3700, BFD sessions are bound to Layer 2 interfaces.
Multi-Hop BFD
Multi-hop BFD detects IP connectivity of paths between two non-directly-connected devices.
These paths may span multiple hops or overlap. Multi-hop BFD is often used to detect reachable
routes between two devices.
The S3700 provides multi-hop BFD for static routes. Generally, static routes do not have the
detection mechanism. When a network fails, the administrator needs to check the static routes
manually. You can use multi-hop BFD to check the status of static routes. The RM module
determines whether a static route is available according to the status of the BFD session.
BFD for Static Routes
Static routes do not have a detection mechanism. When the network fails, the administrator needs
to check the static routes manually.
Through BFD for static routes, the BFD session can be used to detect the status of IPv4 static
routes on a public network. The RM module determines whether the static route is available
according to the BFD session status.
Issue 01 (2011-10-26)
The local discriminator is allocated automatically.
The remote discriminator is learned by the local end.
If the discriminators on the local end are specified manually, the discriminators on the
remote end must also be specified manually.
If you configure a static BFD session with automatically negotiated discriminators on the
local end, you can configure a static BFD session with automatically negotiated
discriminators or configure a dynamic BFD session on the peer end.
If a static BFD session with automatically negotiated discriminators and a dynamic BFD
session are configured at the local end, the following principles are applicable:
– If the dynamic BFD session and static BFD session with automatically negotiated
discriminators share the same configurations (the source address, destination address,
outbound interface, and VPN index), the two BFD sessions coexist.
– If the dynamic BFD session named DYN_local discriminator is configured earlier than
the static BFD session with automatically negotiated discriminators, the name of the
dynamic BFD session is changed to the name of the static BFD session.
– The two BFD sessions use the smaller values of BFD parameters.
NOTE
For details on how to configure BFD for static routes, see Configuring BFD for IPv4 Static Routes on a
Public Network in the Quidway S3700 Series Ethernet Switches Configuration Guide - IP Routing.
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6 BFD Configuration
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