11-6
Cisco SCE 8000 10GBE Software Configuration Guide
OL-30621-02
Chapter 11 Redundancy and Failover
Hot Standby and Failover
Hot Standby and Failover
The failover solution requires two Cisco SCE platforms connected in a cascade manner.
•
•
•
Hardware Crash Mode, page 11-8
•
Failure in the Cascade Connection, page 11-9
•
Installing a Cascaded System, page 11-9
Hot Standby
In failover solution, one of the Cisco SCE platforms is used as the active Cisco SCE platform and the
other is used as the standby. Although traffic enters both the active and the standby Cisco SCE platforms,
all traffic processing takes place in the Cisco SCE platform which is currently the active one. The active
Cisco SCE platform processes the traffic coming on both links, its own link and the link connected to
the standby Cisco SCE platform, as follows
•
All traffic entering the active Cisco SCE platform through its traffic ports is processed in that Cisco
SCE platform and then forwarded to the line.
•
All traffic entering the standby Cisco SCE platform through its traffic ports is forwarded through the
cascade ports to the active Cisco SCE platform where it is processed, and then returned to the
standby Cisco SCE platform through the cascade ports to be forwarded to the original line from
which it came.
Since only one Cisco 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 failover, both Cisco SCE platforms hold subscriber states for all parties, and
subscriber state updates are exchanged between the active Cisco SCE platform and the standby. This
way, if the active Cisco SCE platform fails, the standby Cisco SCE platform is able to start serving the
line immediately with a minimum loss of subscriber-state.
The two Cisco SCE platforms also use the cascade channel for exchanging periodic keep-alive messages.
Failover
In failover solution, the two Cisco SCE platforms exchange keep alive messages via the cascade ports.
This keep alive mechanism enables fast detection of failures between the Cisco SCE platforms and fast
failover to the standby Cisco SCE platform when required.
If the active Cisco SCE platform fails, the standby Cisco SCE platform then assumes the role of the
active Cisco SCE platform.
The failed Cisco 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 Cisco SCE platform, and to
forward processed traffic back to the link. The previously standby Cisco SCE platform now processes
all the traffic of this other link that is forwarded to it by the previously active Cisco SCE platform in
addition to the traffic of its own link.
