Cisco Systems SCE 2000 4/8xFE manual Link Continuity, Bypass Mechanism

Chapter 3 Topology

Topology Considerations

Link Continuity

The bypass mechanism of the SCE 2000 allows traffic to continue to flow, if desired, even if the device itself is not functioning.

Note that when the SCE 2000 is connected to the network through an external switch, a failure of the SCE 2000 does not affect the traffic flow, as the traffic continues to flow through the external switch.

Bypass Mechanism

The SCE 2000 includes a Network Interface Card with a bypass mechanism that is enabled upon SCE 2000 failure. In addition, when connected in-line it can also be enabled in normal operation to simultaneously bypass traffic flow to the other side and direct it internally for analysis. In this case it maintains "receive-only"-like monitoring functions, when control functionality is not required.

The bypass card supports the following four modes:

•Bypass — The bypass mechanism preserves the network link, but traffic is not processed for monitoring or for control.

•Forwarding — This is the normal operational mode, in which the SCE 2000 processes the traffic for monitoring and control purposes.

•Sniffing — The bypass mechanism preserves the network link, while in parallel allowing the SCE 2000 to process the traffic for monitoring only.

•Cutoff — There is no forwarding of traffic, and the physical link is forced down (cutoff functionality at layer 1).

Maintaining the Network Links vs Maintaining SCE 2000 Platform Functionality

When a single SCE 2000 is deployed, the user may decide that in case of a failure, maintaining the network link is more important than providing the SCE 2000 functionality. In this scenario, when the SCE 2000 detects a failure that requires a reboot process for recovering, it immediately switches to Bypass mode, allowing all traffic to bypass the SCE 2000. The SCE 2000 stays in Bypass mode maintaining the network link, albeit without SCE 2000 processing, until the SCE 2000 fully recovers from the failure and is ready to resume normal functioning.

Alternatively, the user may decide that the SCE 2000 functionality is sufficiently crucial to require severing the link if the SCE 2000 platform fails. In this case, when the SCE 2000 detects a failure that requires a reboot process for recovering, it immediately switches to Cutoff mode, stopping all traffic flow. The SCE 2000 stays in Cutoff mode, halting all traffic, until it fully recovers from the failure and is ready to resume normal functioning. In Cutoff the physical interface is blocked, enabling the network device connected to the SCE 2000 to sense that the link is down.

Cisco SCE 2000 4/8xFE Installation and Configuration Guide

OL-7826-05 3-3