Dead Peer Detection (DPD) is a method used by IKE peers to determine if a peer is unresponsive. The interval parameter specifies the time in seconds between sending DPD probes to the peer. According to the official Juniper Networks documentation for the dead-peer-detection configuration statement, the default interval for sending these probes is 10 seconds. This value ensures a balance between timely detection of a dead peer and minimizing unnecessary network traffic.

A. 20 seconds: This is a valid configurable value within the allowed range (2-60 seconds), but it is not the default setting.

B. 5 seconds: This is the default value for the DPD threshold (the number of unanswered probes before a peer is declared dead), not the interval.

D. 40 seconds: This is a valid configurable value within the allowed range, but it is not the default setting.

1. Juniper Networks TechLibrary

dead-peer-detection (Security IKE): This official documentation page explicitly states the default value for the DPD interval.

URL: https://www.juniper.net/documentation/us/en/software/junos/vpn-ipsec/topics/ref/statement/security-edit-dead-peer-detection.html

Quote: Under the interval option description

it states: "Interval at which DPD requests are sent to the peer. Range: 2 through 60 seconds. Default: 10 seconds."