8.11.3 Notes on using graceful restart

• Do not change the configuration during a graceful restart. If the configuration is changed during graceful restart, the graceful restart may fail.

• During graceful restart, the graceful restart auxiliary functionality does not operate.

• If a failure occurs on a neighboring router during graceful restart, graceful restart may fail.

• Even if the graceful restart procedure is successful, communication might stop if the neighboring switch cannot retain the routing information learned from the Switch.

• When the master switch is switched due to a failure, the neighboring switch may detect disconnection before the master switch is switched and relearning by graceful restart is started. Make sure that the disconnection detection time for each protocol is longer than the time required to switch the master switch. The following table summarizes the minimum time to detect disconnection by protocol when operating with the default values.

  • OSPF and OSPFv3:25 seconds

  • BGP4 and BGP4+:100 seconds

• The time required to switch the master switch depends on the number of interfaces. The following table shows the approximate time required for switching the master switch.

  Table 8-13: Estimated time required for switching the master switch

  Number of interfaces#	Time required for switching the master switch (seconds)
  100	20
  250	30
  512	40
  1024	60

  #: When IPv4 addresses and IPv6 addresses are set for the same interface.

  This guideline is for cases where other Layer 3 functions, such as NTP, multicast routing protocols, are not running simultaneously. If these functions operate at the same time, the time required to switch the master switch may become longer.

  Also, the time required to switch the master switch may become longer immediately after the configuration is updated or immediately after the switch is restarted by software update or restore.

• When the master switch is switched, the new master switch remains in the switching status until the graceful restart is completed (the switch status is indicated by Switchover in the operation command show switch).