Cisco DPC User Manual page 64

How Do I Configure My DOCSIS Residential Gateway?
Field
Phase 2 authentication Allows you to select an authentication type for another level of
Phase 2 SA lifetime
64
Description
security. Select one of the following three authentication types:
MD5
SHA
Null (none)
You may choose any authentication type as long as the other end of
the VPN tunnel uses the same method
Note: SHA is recommended because it is more secure.
Allows you to enter the number of seconds for an individual rotating
key to last until a re-key negotiation between each endpoint occurs.
Smaller lifetimes are generally more secure since it would give a
hacker a smaller amount of time to try to crack the key. However, key
negotiation does take up bandwidth, so network throughput is
sacrificed with small lifetimes. The default setting for Phase 2 is 3,600
seconds.
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