Port redundancy for
MIO cards provides an added level of redundancy that minimizes the impact of
network failures that occur external to the system. Examples include switch or
router port failures, disconnected or cut cables, or other external faults that
cause a link down error.
To ensure that
system card and port-level redundancy mechanisms function properly, disable the
Spanning Tree protocol on devices connected directly to any system port.
Failure to turn off the Spanning Tree protocol may result in failures in the
redundancy mechanisms or service outage.
By default, the
system provides port-level redundancy when a failure occurs, or you issue the
port switch to
command. In this mode, the ports on active and standby MIO/UMIO/MIO2 cards have the same MAC address, but since only one
of these ports may be active at any one time there are no conflicts. This
eliminates the need to transfer MAC addresses and send gratuitous ARPs in port
failover situations. Instead, for Ethernet ports, three Ethernet broadcast
packets containing the source MAC address are sent so that the external network
equipment (switch, bridge, or other device) can re-learn the information after
the topology change. However, if card removal is detected, the system sends out
gratuitous ARPs to the network because of the MAC address change that occurred
on the specific port.
redundancy, if a failover occurs, only the specific port(s) become active. For
example; if port 5/1 fails, then port 6/1 becomes active, while all other
active ports on the line card in slot 5 remain in the same active state. In
port failover situations, use the
table command to check that ports are active on both cards and that both
cards are active.
Take care when
administratively disabling a port that is one of a redundant pair. A redundant
pair comprises both the active and standby ports—for example 5/1 and 6/1. If
5/1 is active, administratively disabling 5/1 through the CLI does not make 6/1
active. It disables both 5/1 and 6/1 because an action on one port has the same
effect on both. Refer to
Configuring Ethernet Interfaces and Ports in
Interface and Port Configuration Procedures.
card-level redundancy, there is no port-level redundancy in an MIO/UMIO
failover. The standby MIO/UMIO/MIO2 becomes active and
all ports on that card become active. The system automatically copies all the
MAC addresses and configuration parameters used by the failed MIO/UMIO/MIO2 to its redundant counterpart. The ports on MIOs keep
their original MAC addresses, and the system automatically copies the failed
MIO/UMIO/MIO2's configuration parameters to its redundant
Port redundancy can
be configured to be revertive or non-revertive. With revertive redundancy
service is returned to the original port when service is restored.
requires specific network topologies to work properly. The network must have
redundant switching components or other devices that the system is connected
to. The following diagrams show examples of a redundant switching topologies
and how the system reacts to various external network device scenarios.
Figure 2. Network
Topology Example Using MIO/UMIO Port Redundancy
Figure 3. Port
Redundancy Failover in Cable Defect Scenario
In the example
above, an Ethernet cable is cut or unplugged, causing the link to go down. When
this event occurs, the system, with port-mode redundancy enabled, recognizes
the link down state and makes port 6/1 the active port. The switching device,
using some port redundancy scheme, recognizes the failure and enables the port
on the secondary switch to which the MIO/UMIO/MIO2 in slot 6 is
connected, allowing it to redirect and transport data.
Figure 4. Port
Redundancy Failover in External Network Device Failure Scenario
In the example
above, a switch failure causes a link down state on all ports connected to that
switch. This failure causes all redundant ports on the line card in slot 6 to
move into the active state and utilize the redundant switch.