Chapter 3 Topology
Topology Considerations
SCE 2000 4xGBE Installation and Configuration Guide
OL-7824-02
3-3
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 optical splitter, a failure of
the
SCE 2000
does not affect the traffic flow, as the traffic continues to flow through the optical
splitter.
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.
