Reference Guide

High Availability | 413
-- Line cards --
Slot Status NxtBoot ReqTyp CurTyp Version Ports
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0 online online E48VB E48VB 7-5-1-71 48
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Hitless Behavior
Hitless Behavior is supported only on platforms: c e
Hitless behavior is supported on the S4810 with FTOS 8.3.12.0 and later, the S4820T with FTOS 8.3.19.0
and later, or the E-Series ExaScale
e
x
with FTOS 8.2.1.0. and later.
Hitless is a protocol-based system behavior that makes an RPM failover on the local system transparent to
remote systems. The system synchronizes protocol information on the standby and primary RPMs such
that, the event of an RPM failover, there is no need to notify remote systems of a local state change.
Hitless behavior is defined in the context of an RPM failover only and does not include line card, SFM,
and power module failures.
• On the E-Series: Failovers triggered by software exception, hardware exception, forced failover via the
CLI, and manual removal of the primary RPM are all hitless.
• On the C-Series, S4810, and S4820T: Only failovers via the CLI are hitless. The system is not hitless
in any other scenario.
Hitless protocols are compatible with other hitless and graceful restart protocols. For example, if hitless
OSPF is configured over hitless LACP LAGs, both features work seamlessly to deliver a hitless
OSPF-LACP result. However, if hitless behavior involves multiple protocols, all must be hitless in order to
achieve a hitless end result. For example, if OSPF is hitless but BFD is not, OSPF operates hitlessly and
BFD flaps upon an RPM failover.
The following protocols are hitless:
• Link Aggregation Control Protocol. Refer to Configure LACP as Hitless.
• Spanning Tree Protocol. Refer to Configuring Spanning Trees as Hitless.
• On the E-Series only, Bi-directional Forwarding Detection (line card ports). Refer to Bidirectional
Forwarding Detection (BFD).
S4820T