Cisco Cisco IOS Software Release 12.0(22)S
Frame Relay Fast Restart
Feature Overview
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Cisco IOS Release 12.0(22)S
Accelerating the LMI Cycle
To address the possibility that the line protocol is down upon switchover to the standby RP, the Frame
Relay Fast Restart feature introduces an accelerated Local Management Interface (LMI) cycle. The
accelerated LMI cycle is designed to bring the line protocol up quickly, in turn making PVCs available
sooner.
Relay Fast Restart feature introduces an accelerated Local Management Interface (LMI) cycle. The
accelerated LMI cycle is designed to bring the line protocol up quickly, in turn making PVCs available
sooner.
Before the introduction of Frame Relay Fast Restart, LMI polling cycles occurred every 10 seconds, and
on the sixth cycle a full LMI status request was sent. This pattern resulted in the sending of a full LMI
status request every 60 seconds. With the accelerated LMI cycle, a full status request is sent to the switch
immediately after switchover to the standby RP. The next polling cycle begins within 1 second following
receipt of the full status from the switch rather than waiting the default 10 seconds. A full status request
is also sent at the last polling cycle. The accelerated LMI cycle ends after a fixed number of polling
cycles, which can be configured to meet the requirements of the switch.
on the sixth cycle a full LMI status request was sent. This pattern resulted in the sending of a full LMI
status request every 60 seconds. With the accelerated LMI cycle, a full status request is sent to the switch
immediately after switchover to the standby RP. The next polling cycle begins within 1 second following
receipt of the full status from the switch rather than waiting the default 10 seconds. A full status request
is also sent at the last polling cycle. The accelerated LMI cycle ends after a fixed number of polling
cycles, which can be configured to meet the requirements of the switch.
The accelerated LMI cycle causes the line protocol to come up and PVCs to be reported active in 1 or 2
seconds instead of the 30 to 40 seconds that it would have taken before the introduction of this feature.
seconds instead of the 30 to 40 seconds that it would have taken before the introduction of this feature.
Note
It may take an additional 10 seconds before the remote router sees that the PVCs are up.
Note
The accelerated DTE LMI cycle is nonstandard and may cause problems for some DCE LMI
implementations. When the DTE device is directly connected to a Cisco DCE device that is
terminating PVCs, the DCE device must be running a Cisco IOS software release based on Cisco IOS
Release 12.0(18)ST, 12.0(17.6)S, 12.1(9.1), or 12.2(2.2) or later.
implementations. When the DTE device is directly connected to a Cisco DCE device that is
terminating PVCs, the DCE device must be running a Cisco IOS software release based on Cisco IOS
Release 12.0(18)ST, 12.0(17.6)S, 12.1(9.1), or 12.2(2.2) or later.
Accelerating Inverse ARP
Inverse Address Resolution Protocol (ARP) requests, where applicable, will be sent out as soon as a PVC
becomes active. Before the introduction of the Frame Relay Fast Restart feature, when an Inverse ARP
request was unsuccessful, the request was resent every 60 seconds. This new feature accelerates the
Inverse ARP timer so that if a request comes back unsuccessful, a second request is sent in 10 seconds.
Subsequent requests are sent every 60 seconds.
becomes active. Before the introduction of the Frame Relay Fast Restart feature, when an Inverse ARP
request was unsuccessful, the request was resent every 60 seconds. This new feature accelerates the
Inverse ARP timer so that if a request comes back unsuccessful, a second request is sent in 10 seconds.
Subsequent requests are sent every 60 seconds.
Benefits
The Frame Relay Fast Restart feature increases network availability by reducing the recovery time from
hardware and software failures on Cisco routers in Frame Relay networks. This feature enables PVCs to
be available for use within 10 to 15 seconds of switchover to a standby Route Processor; in contrast,
before the introduction of this feature, it could take from 30 to 90 seconds.
hardware and software failures on Cisco routers in Frame Relay networks. This feature enables PVCs to
be available for use within 10 to 15 seconds of switchover to a standby Route Processor; in contrast,
before the introduction of this feature, it could take from 30 to 90 seconds.
Restrictions
The Frame Relay Fast Restart feature supports only the following interfaces and connections:
•
Serial interfaces
•
DTE LMI type
•
PVCs (switched and terminated)