Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SERVICE AVAILABILITY CONFIGURATION GUIDE 2010-10-08 Configuration Manual page 94

JunosE 11.3.x Service Availability Configuration Guide
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ES2 10G LMs cannot be used as downlink modules in an LNS device. These LMs cannot
be used as access modules in a LNS device that contains a Service IOA that is
HA-enabled.
Certain statistics might be lost during the period of the stateful line module switchover.
PPP and policy statistics are polled and collected every 10 minutes and sent to the
standby line module. The statistics that were last collected before the switchover
occurred are used as the baseline for statistics on the newly configured primary module.
At a maximum, statistics for around 10 minutes might be lost. This scenario normally
happens when polling is about to happen and the primary module switched over.
A historical record of information about the forwarding and drop events and forwarding
and drop rates on egress queues is not retained across a stateful line module switchover.
The queue statistics for subscriber interfaces are calculated afresh after a stateful
switchover of line modules.
Sequence number checking for data packets received on all L2TP tunnels in the router
is not maintained and supported during a stateful line module switchover. We
recommend that you set up the router to ignore sequence numbers in data packets
received on L2TP tunnels by entering the l2tp ignore-receive-data-sequencing
command on an LNS device to prevent requests from a LAC device to enable insertion
of sequence numbers into data packets.
Some performance impact might occur when a new secondary module is provisioned
or inserted, with the primary module containing maximum tunneled PPP sessions. In
this case, data synchronization consumes a portion of the backplane bandwidth, which
might have some impact on call setup rate (CSR) during this time. Under peak load
conditions, it might take about 20 minutes for the system to become HA-active for
Service IOAs.
Removal of the Service IOA from the primary ES2 4G LM without powering it down
does not trigger stateful line module switchover.
The PPP application on ES2 4G LMs with Service IOA supports line module high
availability. PPP session data is mirrored to the standby line module to attain high
availability. The PPP application replicates the PPP sessions on the standby module
and retains them across switchovers, in addition to accounting statistics. During line
module switchover, the forwarding controller (FC) in the access module of the router
that works as the LNS attempts to prevent timeouts of PPP sessions (due to the lack
of PPP echo reply messages to the active subscribers) by sending echo response
packets until the switchover is successfully completed.
Policy manager is stateful line module switchover safe. Policy manager downloads
the policy attachments from the SRP to the newly active line module after a switchover
operation is detected. Policy statistics are preserved and made available across line
module switchovers.
The QoS application accomplishes the stateful line module switchover functionality
by restoring the queues on subscriber interfaces in the newly active line module when
the previously designated primary line module fails.
During stateful line module switchover, the forwarding controller (FC) in the access
module on the router functioning as the LNS device prevents timeouts of PPP sessions
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