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Cisco Bug: CSCuq17045 - AnyConnect blocking DHCPv6 replies causes loss of IPv6 address

Last Modified

Nov 27, 2020

Products (1)

  • Cisco AnyConnect Secure Mobility Client

Known Affected Releases

3.1(4072) 4.0(61)

Description (partial)

AnyConnect reconnects periodically causing VPN traffic drops.
Reconnect might take a couple of seconds or only one second.

Windows 7 loses IPv6 address after AnyConnect VPN is connected because DHCPv6 renew / rebind replies are not getting to DHCPv6-Client Windows process.
The packets are seen with Wireshark on Windows 7 interface, but DHCPv6-Client doesn't get them.

Errors are seen in Windows event log: "DHCPv6-Client, error 1003, Your computer was not able to renew its address from the network".

Windows 7 having IPv4 and IPv6 address on its interface.
IPv6 address assigned using DHCPv6 server, with short renew time.

Preferred lifetime: 30s
Valid lifetime: 60s
T1: 15s
T2: 45s

AnyConnect connecting to the VPN gateway using either IPv4 address or IPV6 address.
For IPv6 reconnects are more frequent.
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