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When IPSec is run over a PPPoE-enabled interface on a router with Cisco IOS version 12.2, "The decapsulation of the packets fail with the following error:00:05:05: IPSEC(decapsulate): error in decapsulation crypto_ipsec_sa_exists error message is received



Thid cocuments describes an issue faced by a user.


What is PPPoE?

PPPoE is used to establish a PPP connection over an Ethernet protocol. DSL Internet connections are created with the help of PPPoE. Generally, DSL modem connect to computers with the help of an Ethernet connection. Therefore, PPPoE enables user to connect to an Internet service provider (ISP) through a DSL modem.


The benefits of using a PPPoE configuration is that:

  • Easy to set up.
  • Supports multiple computers on a local area network (LAN).


The disadvantage of using PPPoE is that it requires an additional overhead or extra data to be sent over the Internet connection.


Core issue

This problem is due to the presence of Cisco bug ID CSCdy76920.



In order to resolve this issue, download and upgrade to Cisco IOS Software Release 12.3(17) or the latest release available.

Version history
Revision #:
2 of 2
Last update:
‎08-23-2017 08:19 PM
Updated by:
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