Avaya Configuring Integrated IP Security Bedienungsanleitung PDF herunterladen (Seite 33)

Getting Started with IPsec

304111-A Rev 00

2-9

Security Protocols

IPsec uses the following encryption services:

• Data Encryption Standard (DES)

• Message Digest 5 (MD5)

ESP uses the cipher block chaining (CBC) mode of the DES encryption

algorithm. CBC is considered the most secure mode of DES. A 56-bit or 40-bit

number that you generate, known as a key, controls encryption and decryption.

Key management is manual.

DES is available in two encryption strengths:

• 56-bit DES keys (recommended)

• 40-bit DES keys

Both sides of an SA must use the same encryption strength. Normally, you should

use the stronger 56-bit DES key. However, if you are communicating with a

security gateway that is limited to a 40-bit DES key, you must use the 40-bit key.

When ESP protection is used in tunnel mode, an “outer” IP header specifies the

IPsec processing destination, and an “inner” IP header specifies the (apparently)

ultimate destination for the packet. The security protocol header appears after the

outer IP header and before the inner one. Only the tunneled packet is protected,

not the outer header.

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Avaya Configuring Integrated IP Security Bedienungsanleitung Seite 33