11-8
Cisco SCE 8000 10GBE Software Configuration Guide
OL-30621-02
Chapter 11 Redundancy and Failover
Hot Standby and Failover
–
Effect on the Cisco SCE platform functionality—Since the active Cisco SCE platform only sees
the traffic of a single link, split-flow effects might occur. The link connected to the failed Cisco
SCE platform gets no service.
Hardware Crash Mode
There are three hardware components that operate together to produce the desired behavior upon failure
of the Cisco SCE 8000 platform:
•
external optical bypass: In a cascade setup, if the traffic links are connected to external optical
bypass modules, the optical bypass may be either activated or deactivated by the hardware during a
failure.
The external optical bypasses protect against a second Cisco SCE 8000 platform failure. In the case
of a second failure, if a bypass module is connected to the last Cisco SCE 8000 to fail, it will be
enabled. This preserves one of the network links, assuming the
on-failure
configuration is is
bypass
. If the
on-failure
configuration is
external-bypass
, the external optical bypass is activated even
during a single failure by the failed Cisco SCE platform.
•
internal electrical bypass: The Cisco SCE 8000 contains internal electrical bypasses connecting SPA
modules 0 and 2 and modules 1 and 3. These bypasses transmit the traffic to and from the cascade
connections between the platforms.
•
SPA modules: Under some conditions (such as if the
on-failure
configuration is
cutoff
), the SPA
modules are disabled when failure occurs.
The collective behavior of these three components is known as the hardware crash mode and is
dependent on the configuration of the
on-failure
parameter of the
connection-mode
command, as well
as whether the platform is the active or standby platform.
In the standby platform, hardware crash mode behavior is as follows for:
For
on-failure bypass
:
•
The external optical bypass, if installed, is deactivated (traffic is sent to the platform).
•
The electrical bypass is enabled (cascade ports transmit traffic to the active platform for processing)
•
The SPA modules are enabled (all ports and links are functioning)
This means that whether the standby platform is operational or has failed, it transmits traffic to the active
platform for processing via the electrical bypasses.
For
on-failure cutoff
:
•
The external optical bypass, if installed, is deactivated (traffic is sent to the platform).
•
The electrical bypass is disabled.
•
The SPA modules are powered off.
This means that if the standby platform fails, the link connected to it Cisco SCE is severed.
For
on-failure external-bypass
:
•
The external optical bypass is activated (traffic is bypassed).
•
The electrical bypass is enabled between ports 0 and 1. (This is a special configuration, done just in
case the optical bypass device does not function, which has a very low probability.)
•
The SPA modules are enabled (all ports and links are functioning)
This means that when the standby Cisco SCE platform is failed, the external optical bypass is used to
ensure link continuity at the expense of not servicing the traffic on that link.
