Table of Contents
Advertisement
Hot Standby and Fail-over
Since only one SCE platform processes all traffic at any given time, split flows, which are caused by
asymmetrical routing, that exist in the two data links are handled correctly.
To support subscriber-state fail-over, both SCE platforms hold subscriber states for all parties, and
subscriber state updates are exchanged between the active SCE platform and the standby. This way, if
the active SCE platform fails, the standby SCE platform is able to start serving the line immediately with
a minimum loss of subscriber-state.
The two SCE platforms also use the cascade channel for exchanging periodic keep-alive messages.
Fail-over
In fail over solution, the two SCE platforms exchange keep alive messages via the cascade ports. This
keep alive mechanism enables fast detection of failures between the SCE platforms and fast fail over to
the standby SCE platform when required.
If the active SCE platform fails, the standby SCE platform then assumes the role of the active SCE
platform.
The failed SCE platform uses its electrical bypass mechanism, which is a hardware entity that is separate
from the main board and processors, to forward traffic to the other SCE platform, and to forward
processed traffic back to the link. The previously standby SCE platform now processes all the traffic of
this other link that is forwarded to it by the previously active SCE platform in addition to the traffic of
its own link.
When the failed SCE platform recovers, it will remain in standby, while the previously standby SCE
platform remains active. Switching the SCE platforms back to their original roles may be performed
manually, if required, after the failed SCE platform has either recovered or been replaced.
If the failure is in the standby SCE platform, it will continue to forward traffic to the active SCE platform
and back to its link, while the active SCE platform continues to provide its normal processing
functionality to the traffic of the two links.
Note
For information regarding the synchronization of subscriber information between cascaded SCE
platforms and the effect of fail-over on the subscriber databases, see
Information in a Cascade System, page
There are two user-configurable options that are relevant in a situation when an SCE platform fails:
•
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
10-6
Bypass — Maintain the link in bypass mode (continue sending traffic to the other SCE platform,
and then continue forwarding the processed traffic back to the link). The incoming traffic in the
failed SCE platform is forwarded to the working SCE platform, where it is processed and then sent
back to the original SCE platform and back to the link.
Effect on the network link — negligible.
–
Effect on the SCE platform functionality — The effect on the SCE platform functionality is
–
dependent on the failed SCE platform.
If the failure is in the standby SCE platform — the active SCE platform continues providing its
–
normal functionality, processing the traffic of the two links.
If the failure is in the active SCE platform — the standby SCE platform takes over processing
–
the traffic, and becomes the active SCE platform.
9-6.
Chapter 10
Redundancy and Fail-Over
Synchronizing Subscriber
OL-7827-12
Advertisement
Table of Contents
