The IPSEC SA lifetime is a fixed configured parameter that cannot be left out. If you have configured IPSEC correct, and you always have interresting IPSEC traffic (traffic that matches your Crypto ACL) the SA will re-establish the tunnel automatically.
A smaller SA lifetime provides more security because this changes your "connection-keys" more often. But again shortes SA life time provides more overhead to manage the connection.
Be aware that you have 2 lifetime settings:
1 for IKE - Key exchange Phase 1
crypto isakmp policy xxx
Default = 24 hours (i believe)
2 for the IPSEC tunnel itselves.
crypto map xxxxx
set security-association lifetime
Default = 1 hour (i believe)
Post your config, and we might help you find your problem.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...