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| Chapter 12 IPSec VPN |
| Table 74 Security > IPSec VPN > IPSec Setting > IKE (continued) | |
| LABEL | DESCRIPTION |
| Integrity | Select SHA1 or MD5 from the |
| Algorithm | Digest 5) and SHA1 (Secure Hash Algorithm) are hash algorithms used |
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| to authenticate packet data. The SHA1 algorithm is generally |
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| considered stronger than MD5, but is slower. Select MD5 for minimal |
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| security and |
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| Select Diffie- | You must choose a key group for key exchange in SA setup. 768bit |
| Hellman Group | refers to |
| for Key | refers to |
| Exchange | Other options include 1536, 2048, and 3072 bit |
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| Key Life Time | Define the length of time before an IKE or IPSec SA automatically |
| (Seconds) | renegotiates in this field. It may range from 60 to 3,000,000 seconds |
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| (almost 35 days). |
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| A short SA Life Time increases security by forcing the two VPN |
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| gateways to update the encryption and authentication keys. However, |
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| every time the VPN tunnel renegotiates, all users accessing remote |
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| resources are temporarily disconnected. |
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| Apply/Save | Click Apply/Save to save your changes back to the |
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| and return to the IPSec screen. |
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12.3.2 Manual Key Setup
Manual key management is useful if you have problems with Auto(IKE) key management.
12.3.2.1 Security Parameter Index (SPI)
An SPI is used to distinguish different SAs terminating at the same destination and using the same IPSec protocol. This data allows for the multiplexing of SAs to a single gateway. The SPI (Security Parameter Index) along with a destination IP address uniquely identify a particular Security Association (SA). The SPI is transmitted from the remote VPN gateway to the local VPN gateway. The local VPN gateway then uses the network, encryption and key values that the administrator associated with the SPI to establish the tunnel.
Current ZyXEL implementation assumes identical outgoing and incoming SPIs.
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