Reference Guide

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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 (see Link Aggregation Control Protocol (LACP))
• Spanning Tree Protocol (see Configuring Spanning Trees as Hitless)
• Bi-directional Forwarding Detection (see Bidirectional Forwarding Detection (BFD))
Graceful Restart
Graceful Restart is supported on a stacked S5000 switch. Graceful restart (also called non-stop forwarding)
is a protocol-based mechanism that preserves the forwarding table of the restarting router and its neighbors
for a specified period to minimize the loss of packets. A graceful-restart router does not immediately
assume that a neighbor is permanently down and so does not trigger a topology change.
FTOS supports graceful restart for the following protocols:
• Border Gateway Protocol.
• Open Shortest Path First.
• Protocol Independent Multicast—Sparse Mode.
• Intermediate System to Intermediate System.
Software Resiliency
During normal operations FTOS monitors the health of both hardware and software components in the
background to identify potential failures, even before these failures manifest.
System Health Monitoring
FTOS also monitors the overall health of the system. Key parameters like CPU utilization, free memory,
and error counters (CRC failures, packet loss, etc.) are measured, and upon exceeding a threshold can be
used to initiate recovery mechanism.
Failure and Event Logging
Dell Networking systems provide multiple options for logging failures and events.