Asymmetric Routing Topology; Asymmetric Routing And Other Service Control Capabilities - Cisco SCE8000 Installation And Configuration Manual

Chapter 3 Cisco SCE8000 Topology and Topology-Related Parameters
In a single Cisco SCE8000 topology, the value of this parameter is determined by whether or not the link
can be completely cut when the Cisco SCE8000 fails, or whether traffic flow should continue across the
link in spite of platform failure. In the latter case, the External-bypass mode is the recommended
setting, and is therefore the default value for the on-failure mode parameter.
In a dual cascaded Cisco SCE8000 topology, the default on-failure mode is Bypass, since it preserves
full traffic processing functionality on both links in most single box failures (as long as the SPA interface
card is functioning properly).
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Asymmetric Routing Topology

In some Service Control deployments, asymmetrical routing occurs between potential service control
insertion points. Asymmetrical routing can cause a situation in which the two directions of a
bi-directional flow pass through different SCE platforms, resulting in each SCE platform seeing only
one direction of the flow (either the inbound traffic or the outbound traffic).
This problem is typically solved by connecting the two SCE platforms in cascade mode (or through an
MGSCP cluster), thereby making sure that both directions of a flow run through the same SCE platform.
However, this is sometimes not feasible, due to the fact that the SCE platforms sharing the split flow are
geographically remote (especially common upon peering insertion). In this type of scenario, the
asymmetric routing solution enables the SCE platform to handle such traffic, allowing SCA BB to
classify traffic based on a single direction and to apply basic reporting and global control features to
uni-directional traffic.

Asymmetric Routing and Other Service Control Capabilities

Asymmetric routing can be combined with most other Service Control capabilities, however there are
some exceptions.
Service Control capabilities that cannot be used in an asymmetric routing topology include the
following:
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Cutoff mode is suggested for the following:
Non-redundant inline topology if value-added services (such as security) are crucial and are
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more important than maintaining connectivity.
Bypass mode is suggested for the following:
Non-redundant inline topology if connectivity is of high importance.
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In redundant inline setups, if cutoff or traffic loss on a single link for a period of up to ten
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minutes (during a rare event of a SPA interface card failure) can be tolerated.
External-bypass mode is suggested for the following:
Non-redundant inline topology if connectivity is crucial.
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Redundant inline setups, if connectivity is crucial. Note that when this mode is used, the link
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connected to the failed box is not serviced, and the other link operates with asymmetric routing
functionality.
Subscriber redirect
Subscriber notification
Any kind of subscriber integration. (Use subscriber-less mode or anonymous subscriber mode
instead)
Cisco SCE8000 Installation and Configuration Guide, Rel 3.1.7
Asymmetric Routing Topology
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