Graceful Restart; Software Resiliency - Dell Force10 C150 Configuration Manual

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: 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. See
• Spanning Tree Protocol. See
• On the E-Series only, Bi-directional Forwarding Detection (line card ports). See
Forwarding Detection on page

Graceful Restart

Graceful Restart
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. On E-Series, when you configure graceful restart, the system drops
no packets during an RPM failover for protocol-relevant destinations in the forwarding table, and is
therefore called "hitless". On the C-Series and S-Series, packet loss is non-zero, but trivial, and so is still
called hitless.
FTOS supports graceful restart for the following protocols:
• Border Gateway Protocol. See
• Open Shortest Path First.
• Protocol Independent Multicast—Sparse Mode.
• Intermediate System to Intermediate System.
System," on page

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.
390 | High Availability
Configuring Spanning Trees as Hitless on page
169.
is supported on platform:
Enable graceful restart on page
Graceful Restart on page
507.
Configure LACP as Hitless on page
e c s
241.
700.
PIM-SM Graceful Restart on page
Chapter 23, "Intermediate System to Intermediate
549.
1064.
Bidirectional
764.