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PPP Encryption Control Protocol (ECP) and Encryption Algorithms
(Page 2 of 4)
ECP Operation: Compression Setup
Like CCP, ECP is analogous to the
Control Protocols (NCPs) that negotiate
parameters specific to a network layer protocol sent on the link, but
deals with how devices encrypt data rather than how they transport layer
three traffic. This also means that like the NCPs, ECP is a "lite" version
of LCP and works in the same basic way. Once an ECP link is negotiated,
encrypted frames can be sent between devices. When no longer needed,
the ECP link can be terminated.
ECP uses the same subset of seven
LCP message types that the NCPs use, and adds two more. The use of these
messages for each of the life stages of an ECP link is as
- Link Configuration: Like the NCPs (and
also like CCP of course), encryption configuration is done once ECP
reaches the Network-Layer Protocol phase. The process of setting
up encryption and negotiating parameters is accomplished using Configure-Request,
Configure-Ack, Configure-Nak and Configure-Reject
messages just as
described in the LCP topic, except the
configuration options are particular to ECP.
- Link Maintenance: Code-Reject messages
can be sent to indicate invalid code values in ECP frames. The two new
message types are Reset-Request and Reset-Ack, which are
used to reset the encryption (the ECP link) in the event of a detected
failure in decryption.
- Link Termination: An ECP link can be terminated
using Terminate-Request and Terminate-Ack. Again, remember
that like the NCP links, the ECP link is set up within an LCP link,
so closing it doesn't terminate the LCP link.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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