IP Security - Virtual Private Network
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
Alcatel-Lucent
IP
SEC PROTOCOLS
The IPsec protocol suite consists of two protocols:
• “Authentication Header (AH)”
• “Encapsulating Security Payload (ESP)”
A
UTHENTICATION HEADER (AH)
An Authentication Header (AH) for an IP permits communicating parties to verify
that data was not modified in transit and that it was genuinely transmitted from the
apparent source.
This protocol provides a means to verify the authenticity/integrity of the content
and origin of a packet. A packet can be authenticated by the checksum calculated
via hash-based message authentication code (HMAC) using a secret key and
either MD-5 or SHA-1 hash functions.
• Message Digest version 5 (MD5) - An algorithm that produces a 128-bit hash
(also called a digital signature or message digest) from a message of arbitrary
length and a 16-byte key. The resulting hash is used, like a fingerprint of the
input, to verify content and source authenticity and integrity.
• Secure Hash Algorithm-1 (SHA-1) - An algorithm that produces a 160-bit hash
from a message of arbitrary length and a 20-byte key. It is generally regarded as
more secure than MD5 because of the larger hashes it produces.
E
NCAPSULATING SECURITY PAYLOAD (ESP)
An Encapsulation Security Payload (ESP) format for IP is applied to encrypt the
data. This provides for enhanced security of the data packet and protects it
against eavesdropping during transit.
The ESP protocol provides a means to ensure privacy (encryption), source
authentication, and content integrity (authentication). In tunnel mode it
encapsulates the entire IP packet (header and payload), and then appends a new
IP header to the now encrypted packet. This new IP header contains the
destination address needed to route the protected data through the network.
Note: The OmniAccess 5740 USG supports the ESP protocol, which also provides AH
functionality.
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