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Overview of IPsec

304111-B Rev 00

1-5

IPsec Tunnel Mode

When there is a security gateway at each end of a communication, the security

associations between the gateways are said to be in tunnel mode. The tunnel

metaphor refers to data being visible only at the beginning and end points of the

communication. The IP packets protected by IPsec have regular, “visible” IP

headers, but the packet contents are encrypted, and thus hidden. All BayRS IPsec

communications occur in tunnel mode. Tunnel mode is especially effective for

isolating and protecting enterprise traffic traveling across a public data network, as

shown in Figure 1-1.

Elements of IPsec

IPsec has three important constructs:

• Security gateways

• Security policies

• Security associations (SAs)

In the IPsec context, hosts communicate across an untrusted network through

security gateways (routers configured for IPsec interfaces). Security policies

determine how the IPsec interfaces handle data packets for the hosts on both ends

of a connection. Security associations apply IPsec services to data packets

traveling between the security gateways.

Figure 1-2

shows the logical relationship between security policies and security

associations.

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