Provides platform, feature, timer, and interoperability limitations that apply to BFD sessions, including echo mode, bundle behavior, and profile constraints.
Demand mode is not supported in Cisco IOS XR software.
Echo mode and echo-related features are restricted on specific interface types.
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Echo latency detection and echo validation are not supported on bundle interfaces.
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Echo mode is not supported on BFD over bundle interfaces and on bundle VLANS, which is BFD over logical bundle (BLB).
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BFD over unnumbered interfaces is not supported on Cisco 8000 Series routers, regardless of whether echo mode is enabled or disabled.
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Enabling Unicast Reverse Path Forwarding (uRPF) on a physical main and sub interface can cause BFD session flaps because BFD Echo mode (enabled by default) cannot coexist with uRPF on the same interface.
Resource and scaling limitations apply to BFD session configurations.
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When BFD echo mode is enabled for IPv4, the maximum supported number of BFDv4 single-hop sessions is reduced by 50%. This limitation does not apply to BFDv6 or BFDv4 multi-hop sessions.
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On centralized platforms, when the maximum number of timer profiles (8) is reached, RPFO BFD offload sessions cannot be initiated.
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The maximum Tx interval supported is 1 second. Any higher configured value is automatically adjusted to 1 second.
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A maximum of eight unique interval profiles (Desired minimum Tx interval, Required minimum Rx interval, Detection Time Multiplier) are supported across all BFD sessions.
Protocol and feature compatibility constraints must be observed.
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Virtual Router Redundancy Protocol (VRRP) and Hot Standby Router Protocol (HSRP) are not supported as BFD clients.
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If a UMPP ACL denies with logging enabled, packets are not dropped and the BFD session can establish; if it denies without logging, packets are dropped, preventing BFD session establishment.
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If peer routers have mismatched BFD configurations, with one router configured with bundle coexistence bob-blb logical command and the other not, the BFD session may behave unexpectedly.
The bundle coexistence bob-blb logical command is specific to Cisco IOS XR. Configure this command identically on all peer nodes for consistent BFD behavior.