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Initial Public Release
The IP phone freezes, reboots, and disconnects from the VPN after an upgrade from Cisco IOS® Software Release 15.3(3)M3 to Cisco IOS Software Release 15.3(3)M4.
The problem is caused by the Cisco IOS code change, which expects a Datagram Transport Layer Security (DTLS) header from the phone. Specifically, the X-DTLS-Header-Pad-Length attribute in the CONNECT message.
The phones hit two additional bugs (see the CDETS section) and are unable to complete the process. As a result, the phones fall back to TLS which causes the indicated behavior.
The VPN client that runs in the phone firmware is not based on the AnyConnect client, but instead uses the AnyConnect protocol.
All firmware versions that support DTLS, Cisco IOS Software Releases 15.3(3)M4 and 15.4(3)M5 and later, are affected.
The IP phone freezes, reboots, and disconnects from the VPN after an upgrade from Cisco IOS Software Release 15.3(3)M3 to Cisco IOS Software Release 15.3(3)M4.
Cisco IOS version 15.4(3)M4 can be used as a workaround because it does not contain the code change to expect a DTLS header from the phone.
Cisco recommends to use Cisco IOS Software Release 15.4(3) M4 per the workaround.
To follow the bug ID link below and see detailed bug information, you must be
a registered customer and you must be logged in.
|CSCup56792 (registered customers only)
||Supporting 4 byte DTLS header: This bug is raised to track the migration of DTLS header from 1 byte to 4 bytes to improve performance.
|CSCte01414 (registered customers only)
||[DTLS] CDTP Header length shall be negotiable: This is an enhancement to AnyConnect. This is not a bug.
|CSCuy90621 (registered customers only)
||78xx/88xx do not support X-DTLS-Header-Pad-Length:
For More Information
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