TMS zl Management and Configuration Guide ST.1.1.100430

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Virtual Private Networks
Configure an IPsec Site-to-Site VPN with IKE
13. Optionally, select the Enable PFS (Perfect Forward Secrecy) for keys check
box, which forces the tunnel endpoints to generate new keys for the IPsec
SA. In the list that is displayed, select one of the following:
• Group 1 (768)
• Group 2 (1024)
• Group 5 (1536)
The group determines the length of the prime number used during the
exchange. The larger the number, the more secure the key generated by
the exchange.
14. For SA Lifetime in seconds, type a value between 300 (5 minutes) and 86400
(24 hours). Or type 0 if you do not want to specify a lifetime in seconds
(in this case, you must specify a lifetime in kilobytes).
This setting determines how long the IPsec SA remains open. When the
lifetime of the SA reaches 80 percent of the total lifetime, the TMS zl
Module checks whether the SA has experienced any activity. If it has, the
module negotiates a new SA and then deletes the old SA. If the SA is
inactive, the module waits for the complete lifetime to expire. Then, if the
SA is still inactive, the module deletes the SA.
The default value is 28800 (8 hours).
15. For SA Lifetime in Kilobytes, type a value between 2560 and 4194304. Or
leave the default 0 if you do not want to specify a lifetime in kilobytes (in
this case, you must specify a lifetime in seconds).
This setting determines when an SA expires based on the amount of data
passed over it, rather than by time. (The more traffic sent over a connec-
tion, the better chance a hacker has at cracking a key.)
The TMS zl Module checks an IPsec SA for inactivity when the SA has
transmitted and received 80 percent of the allowed bandwidth in kilo-
bytes. If the SA is active, the module renegotiates it, deleting the old SA
when the new one is established. The module deletes an inactive SA if it
is still inactive when the total lifetime in kilobytes is reached.
Note If you specify the SA lifetime both in seconds and in kilobytes, the SA is
evaluated when the first limit is reached.
16. Click Next.