Configuration Guide User guide

FastIron Configuration Guide 333
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Hitless stacking
Hitless stacking configuration notes and feature limitations
• For hitless stacking on the FCX, Brocade recommends that you configure the IronStack MAC
address using the stack mac command. Without this configuration, the MAC address of the
stack will change to the new base MAC address of the Active Controller. This could cause a
spanning tree root change. Even without a spanning tree change, a client (for example, a
personal computer) pinging the stack might encounter a long delay depending on the client
MAC aging time. The client won’t work until it ages out the old MAC address and sends ARP
requests to relearn the new stack MAC address. Refer to “Manually allocating the IronStack
MAC address” on page 275.
• Layer 3 multicast traffic is not supported by hitless stacking.
• After a switchover or failover, the Syslog may contain invalid (non-existent) port numbers in
messages such as “Interface<portnum> state up". This is because some messages from the
old Active Controller will remain in the Syslog after a switchover or failover.
• Failover for devices connected to the management port is not supported. For example, if during
a failover, an end station is connected to the stack through the management port of the Active
Controller, the connection will be shut down. After the failover, the management port on the
new Active Controller will work.
• The following describes hitless stacking limitations with software-based licensing for BGP:
- To enable BGP on a stack unit, you should have an appropriate BGP license installed on all
the stack units.
- If the Active Controller has a BGP license but any other unit in the stack does not have, you
cannot enable BGP on the stack unit.
- If the Active Controller is not running BGP, a stack unit is operational regardless of whether
the Active Controller or stack units have a BGP license or not.
- If the Active Controller is running BGP, and a unit without a BGP license joins the stack, the
unit is put into a non-operational state. But, If a user copies the BGP license to a
non-operational unit, it must take effect immediately and becomes operational. Or, if the
user disable BGP, Active Controller will again put all the non-operational units in
operational mode.
What happens during a hitless stacking switchover or
failover
This section describes the internal events that enable a controlled or forced switchover to take
place in a hitless manner, as well as the events that occur during the switchover.
Real-time synchronization among all FCX units in a stack
Hitless stacking requires that the Active Controller, Standby Controller, and stack members are fully
synchronized at any given point in time. This is accomplished by baseline and dynamic
synchronization of all units in a stack.
When an FCX stack is first booted and becomes operational, baseline synchronization occurs
across all of the units in the stack. The Active Controller copies the current state of its CPU to all
units of the stack, including the Standby Controller. The information received from the Active
Controller is programmed locally in hardware on all units. The information includes: