OSPF fast hello packets

OSPF fast hello packets are hello packets that

  • are sent at intervals of less than 1 second,

  • are achieved by using the OSPF dead-interval command with a dead interval set to 1 second, and

  • use a hello-multiplier value set to the number of hello packets sent during that 1 second.

Fast hello packet behavior

When fast hello packets are configured on the interface, these behaviors occur:

  • The hello interval advertised in the hello packets that are sent out this interface is set to 0.

  • The hello interval in the hello packets received over this interface is ignored.

The dead interval must be consistent on a segment, whether it is set to 1 second (for fast hello packets) or set to any other value. The hello multiplier need not be the same for the entire segment as long as at least one hello packet is sent within the dead interval.

To understand fast hello packets, you should already understand the relationship between OSPF hello packets and the dead interval. See OSPF hello interval and dead interval.