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Unexpected L2TP Failover of Established Tunnels During Unified ISSU
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Copyright © 2010, Juniper Networks, Inc.
IS-IS support for unified ISSU does not depend on this configuration. If you do not issue
the overload advertise-high-metric issu command, the unified in-service software
upgrade can still proceed to successful completion without disrupting IS-IS functionality.
Application Support for Unified ISSU on page 115
L2TP never declares itself as unified ISSU unsafe. However, unified ISSU forces an L2TP
failover for all established tunnels. Successful recovery of a tunnel and its sessions
following the unified in-service software upgrade requires a successful L2TP failover
resynchronization, either by the L2TP silent failover method or the L2TP failover protocol.
When the L2TP silent failover method is configured on ERX1440 router, use the l2tp
retransmission command to set the retransmission retry count to 8 for the remote peers.
A value of more than 7 helps ensure that the remote peers keep retransmitting control
messages for the duration of the unified ISSU warm restart and the tunnels are not
disconnected.
See Specifying the Number of Retransmission Attempts.
When the unified ISSU operation attempts to verify the upgrade prerequisites, a warning
message is generated if any tunnels are present for which failover resynchronization is
disabled.
You can use the show l2tp tunnel failover-resync disable command to identify the
tunnels referred to by the warning message. The command enables filtering based upon
the effective failover resynchronization mechanism:
host1#show l2tp tunnel failover-resync disable
L2TP tunnel 2/1 is Up with 1 active session
1 L2TP tunnel found
If a successful failover resynchronization cannot be performed for a tunnel following the
upgrade, then the tunnel and all of its sessions are subject to disconnection.
L2TP automatically detects a peer L2TP disconnect after the unified in-service software
upgrade is completed by detecting a control channel failure.
When peer LNSs are not configured with PPP keepalives or inactivity timeouts, you must
configure an inactivity timeout for L2TP on the LAC. This timeout enables the router to
detect a PPP disconnect when signaling has been dropped during the unified ISSU
forwarding interruption. In the absence of this configuration, the connection at the LAC
and LNS is left as logged in for an extended period of time following the upgrade.
Application Support for Unified ISSU on page 115
Chapter 5: Configuring a Unified In-Service Software Upgrade
131
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