If the peer doesn't respond with the R-U-THERE-ACK the VPN Client starts retransmitting R-U-THERE messages every five seconds until Peer response timeout is reached. After that the peer is declared dead. The only parameter that can be configured on the Cisco VPN Client is Peer response timeout. You cannot disable DPD in Cisco VPN Client GUI or configuration files. DPD is always used if negotiated with a peer.
https://supportforums.cisco.com/document/32546/dead-peer-detection
DPD is disabled by default on Cisco routers. The default mode is on-demand if not specified. If the peer doesn't respond with the R-U-THERE-ACK the router starts retransmitting R-U-THERE messages every <retry-interval> seconds with a maximum of five retransmissions. After that the peer is declared dead.
https://supportforums.cisco.com/document/32546/dead-peer-detection
DPD in IPSec VPN Client 4.8 - 5.0.04.0300. It seems that Cisco VPN Client sends its R-U-THERE message to a peer if it has sent traffic to the peer, but hasn't received response back within ten seconds.
https://supportforums.cisco.com/document/32546/dead-peer-detection
As part of building an IPsec VPN gateway on a Cisco router, readers will learn how to implement ISAKMP policies using IKE to ensure secure VPN configuration. 1  Creating a full-crypto Cisco IPsec VPN gateway with 2  ... Full-crypto Cisco IPsec VPN gateway with software  ... What is the ISAKMP policy and how does it impact ...
http://searchenterprisewan.techtarget.com/feature/IPsec-VPN-router-configuration-The-ISAKMP-policy
The IPsec Dead Peer Detection Periodic Message Option feature is used to configure the router to query the liveliness of its Internet Key Exchange (IKE) peer at regular intervals. The benefit of this approach over the default approach (on-demand dead peer detection) is earlier detection of dead peers.
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dplane/configuration/12-4/sec-ipsec-data-plane-12-4-book/sec-ipsec-dead-peer.html
Using the IPsec Dead Peer Detection Periodic Message Option. With the IPsec Dead Peer Detection Periodic Message Option feature, you can configure your router so that DPD messages are forced at regular intervals. This forced approach results in earlier detection of dead peers.
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dplane/configuration/12-4/sec-ipsec-data-plane-12-4-book/sec-ipsec-dead-peer.html
ISAKMP policies that support IPsec client connections have two policy components: the ISAKMP policy and the IKE Mode Configuration policy. The client ISAKMP policy should have the lowest priority if the router is going to support peer relationships between IPsec gateways and IPsec clients.
http://searchenterprisewan.techtarget.com/feature/IPsec-VPN-router-configuration-The-ISAKMP-policy
Dead Peer Detection (DPD) is a method that allows detection of unreachable Internet Key Exchange (IKE) peers. DPD is described in the informational RFC 3706: A Traffic-Based Method of Detecting Dead Internet Key Exchange (IKE) Peers authored by G. Huang, S. Beaulieu, D. Rochefort.
https://supportforums.cisco.com/document/32546/dead-peer-detection
Setting up an IOS router to utilize IPsec starts with the configuration of the ISAKMP policy and the router's ISAKMP authentication key data. If the router will be peering with only one other router in a site-to-site topology, the ISAKMP configuration ends there. However, if the router will also be supporting client-to-site peering an additional IKE Mode Configuration is needed as well.
http://searchenterprisewan.techtarget.com/feature/IPsec-VPN-router-configuration-The-ISAKMP-policy
With ISAKMP keepalives enabled, the router sends Dead Peer Detection (DPD) messages at intervals between 10 and 3600 seconds. In the event that a response to a DPD is not received, the router then sends the DPD messages at a more aggressive rate -- between 2 and 60 seconds.
http://searchenterprisewan.techtarget.com/feature/IPsec-VPN-router-configuration-The-ISAKMP-policy
vpn router dead peer detection values
The VPN router dead peer detection values is 4.8 - 5.0.04.0300. Dead peer detection values of a VPN router is 4.8 to 5.0.04.0300.