Port redundancy for
line cards and SPIOs 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 line 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 line cards (for example,
17/1 and 33/1) 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 an line 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 17/1 fails, then port 33/1 becomes active, while all other
active ports on the line card in slot 17 remain in the same active state. In
port failover situations, use the
table commands 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 17/1 and 33/1. If
17/1 is active, administratively disabling 17/1 through the CLI does not make
33/1 active. It disables both 17/1 and 33/1 because an action on one port has
the same effect on both. Refer to
Redundancy below, and
Configuring Ethernet Interfaces and Ports in
Interface and Port Configuration Procedures.
redundancy is initiated, there is no port-level redundancy in a line card or
SPIO failover. The standby line card or SPIO becomes active and all ports on
that card become active. With line cards, the system automatically copies all
the MAC addresses and configuration parameters used by the failed line card to
its redundant counterpart. The ports on SPIOs keep their original MAC
addresses, and the system automatically copies the failed SPIO's configuration
parameters to its redundant counterpart. The packet processing card
automatically re-routes to its redundant line card.
With the SPIO cards,
any time there is a port or card switch gratuitous ARPs are sent.
Be aware that in
the case of a system with only one SMC and two SPIO cards, both SPIOs come up
online. Automatic switching of Ethernet ports does not occur in this scenario,
but you can initiate card and port switching by using the
card spio switch
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 1. Network Topology Example Using Line Card Port
Figure 2. Port Redundancy Failover in Cable Defect
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 33/1 the active port. The switching devices,
using some port redundancy scheme, recognizes the failure and enables the port
on the secondary switch that the line card in slot 33 is connected to, allowing
it to redirect and transport data.
Figure 3. Port Redundancy Failover in External Network Device Failure
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 33 to
move into the active state and utilize the redundant switch.