Concept Guide
deliver a hitless OSPF-LACP result. However, to achieve a hitless end result, if the hitless behavior involves multiple protocols, all protocols
must be hitless. For example, if OSPF is hitless but bidirectional forwarding detection (BFD) is not, OSPF operates hitlessly and BFD aps
upon an RPM failover.
The following protocols are hitless:
• Link aggregation control protocol.
• Spanning tree protocol. Refer to Conguring Spanning Trees as Hitless.
Graceful Restart
Graceful restart (also known as non-stop forwarding) is a protocol-based mechanism that preserves the forwarding table of the restarting
router and its neighbors for a specied 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. Packet loss is non-zero, but trivial, and so is still called hitless.
Dell EMC Networking OS supports graceful restart for the following protocols:
• Border gateway
• Open shortest path rst
• Protocol independent multicast — sparse mode
• Intermediate system to intermediate system
Software Resiliency
During normal operations, Dell EMC Networking OS monitors the health of both hardware and software components in the background to
identify potential failures, even before these failures manifest.
Software Component Health Monitoring
On each of the line cards and the stack unit, there are a number of software components. Dell EMC Networking OS performs a periodic
health check on each of these components by querying the status of a ag, which the corresponding component resets within a specied
time.
If any health checks on the stack unit fail, the Dell EMC Networking OS fails over to standby stack unit. If any health checks on a line card
fail, Dell EMC Networking OS resets the card to bring it back to the correct state.
System Health Monitoring
Dell EMC Networking OS also monitors the overall health of the system.
Key parameters such as CPU utilization, free memory, and error counters (for example, CRC failures and packet loss) are measured, and
after exceeding a threshold can be used to initiate recovery mechanism.
High Availability (HA)
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