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Cisco Bug: CSCuo93772 - VPN Connection Fails with Error "MTU too small"

Last Modified

Jul 03, 2018

Products (1)

  • Cisco AnyConnect Secure Mobility Client

Known Affected Releases

3.1(5160)

Description (partial)

Symptom:
When trying to connect from a machine with a physical interface MTU of 1366 or lower, AnyConnect sometimes fails with the error message "The client's MTU configuration sent from the secure gateway is too small.  A value of at least 1280 is required in order to tunnel IPv6 traffic.  Please contact your network administrator."

Conditions:
Seen using AnyConnect 3.1.05160 and ASA version 9.1(5), with physical interface MTU between 1357 and 1368.

Related Community Discussions

SSL VPN Anyconnect client MTU issue
Hi All,   I am facing an issue while i connect to a few of my remote sites through SSL VPN Anyconnect. (other locations don't show this error) The error comes up within 2 mins after i am connected. Attached is the snapshot.   Note:- Few locations have ASA and a rest Cisco 2811 routers.   Error:-   The clients MTU configuration sent from the secure gateway is too small. A value of at least 1280 is required in order to tunnel IPv6 traffic. Please contact your network administrator.
Latest activity: Jul 06, 2017
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