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Information About Redundancy and Fail-Over
Failure Detection
The SCE platform has several types of mechanisms for detecting failures:
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Link Failure Reflection
The SCE platforms are transparent at Layers 2 and 3. The SCE platform operates in promiscuous mode,
and the network elements on both sides of the SCE platform, are using the MAC address of the other
network element when forwarding traffic.
To assist the network elements on both sides of the SCE platform to identify the link failures as quickly
as possible, the SCE platform supports a functionality of reflecting to the other side of the SCE platforms
events of link failure. When the link on one side of the SCE platform fails, the corresponding link on the
other side is forced down, to reflect the failure. Link failure reflection is done on the traffic ports. When
operating in deployments of single SCE platform with two data links, link failure is reflected between
the two ports of each link.
When working with two cascaded SCE platforms, link failure is reflected in two cases:
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Link failure reflection is supported both when the SCE platform is operational and when it is in
failure/boot status.
Link reflection, like fail-over, is dependent on the bypass mechanism of the SCE platform
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
10-4
Internal failure detection — The SCE platform monitors for hardware and software conditions such
as overheating and fatal software errors.
Inter-device failure detection — The SCE platform sends periodic keep-alive messages via the
cascade ports
SCE platform-Subscriber Manager (SM) communication failure detection — A failure to
communicate with the SM may be regarded as a cause for fail over. However, this communication
failure is not necessarily a problem in the SCE platform. If the connection to the SM of the active
SCE platform has failed, while the connection to the SM of the standby SCE platform is alive, a fail
over process will be initiated to allow the SCE platform proper exchange of information between
the SCE platforms and the SM.
Link failure — The system monitors all three types of links for failures:
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Traffic port link failure — Traffic cannot flow through the SCE platform.
Cascade port link failure — Traffic cannot flow between the SCE platforms through the cascade
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ports.
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Management port link failure — This is not a failure that interrupts traffic on the link in and of
itself. However, when SM is used, management port link failure will cause an SM connection
failure and this, in turn, will be declared as a failure of the SCE platform.
This type of failure, in most cases, does not require reboot of the SCE platform. When the
connection with the SM is re-established the SCE platform is again ready for hot standby. If both
SCE platforms lose their connections with the SM, it is assumed that it is the SM which has failed,
thus, no action will be taken in the SCE platform.
Reflection between the traffic ports of each SCE platform.
If there is a failure in the cascade port link, the two SCE platforms can no longer support proper
processing of the two links, since the traffic flowing on the standby SCE platform's link must be
forwarded to the active SCE platform for processing. In this case the link failure is reflected from
the cascade ports to the traffic ports of the standby SCE platform, in order to force the network to
switch all the traffic only through the link of the active SCE platform.
Chapter 10
Redundancy and Fail-Over
OL-7827-12
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