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Chapter 2 Networking
IEEE 802.1Q-2014 Rapid Spanning Tree Protocol
(RSTP)
It is possible to create loops in a network using the cDAQ-9185/9189. To prevent these loops
from disrupting the network, the cDAQ chassis implements the IEEE 802.1Q-2014 Rapid
Spanning Tree Protocol (RSTP). Using this protocol, each cDAQ chassis is able to find the
shortest path for incoming packets to reach the rest of the network. When multiple paths exist,
this adds a form of redundancy. If a link fails, the protocol automatically switches to use the
redundant link. This process can take several seconds in some cases.
To gain these benefits on external switches connected to the cDAQ chassis, 802.1w (RSTP) must
be enabled. All external switches must be configured to allow the cDAQ chassis to transmit
802.1w packets, known as Bridge Protocol Data Units (BPDU). If any switch has a feature—
such as “BPDU guard”—enabled, the port connected to the cDAQ chassis is disabled and
communication is lost. Refer to the documentation for your external switch for information
about enabling RSTP and disabling BPDU guards on the switch.
Chassis MAC Addresses
The cDAQ chassis is associated with two MAC addresses—both of which are labeled on the
chassis—device and switch. These MAC addresses are not associated with a particular Ethernet
port, but both addresses can appear on both ports as necessary.
The switch MAC address is used to implement the following switch protocols:
• IEEE 802.1AS-2011 (Precision Time Protocol)
• IEEE 802.1Q-2014 (Rapid Spanning Tree Protocol [RSTP] implemented)
The switch MAC address only appears in packets exchanged between the switch embedded in
the cDAQ chassis and the next Ethernet device. It will not propagate further in a properly
configured network. For more information about the recommended configurations for
networking the cDAQ chassis, refer to the Topology Options section.
Table 2-1. NI MAX Device and Switch MAC Addresses
Device MAC Address Switch MAC Address
Associated with the chassis’ IP address Associated with the internal Ethernet
switch—not associated with the chassis’ IP
address
Used by normal device traffic Used for Ethernet protocols for network
configuration and synchronization
Listed in MAX Not listed in MAX
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