Bridging Protocols
Bridged networks use the following protocols:
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STP is the default protocol that is used by the bridged networks. Bridging uses the STP mechanism to prevent network loops that potentially render the subnetworks unusable. To forward packets to their destinations, bridges must listen in promiscuous mode on every link that is attached to the bridge. Listening in promiscuous mode causes bridges to become vulnerable to the occurrences of forwarding loops, in which packets infinitely circle at full-line rate.
Caution - Do not configure a link into a bridge when the highest possible levels of performance are required. Bridging requires the underlying interfaces to be in promiscuous mode, which disables a number of important optimizations that are in the hardware (NIC), driver, and other layers of the system. The disabling of these performance enhancements is an unavoidable consequence of the bridging mechanism. These performance issues only affect links that are configured to be part of a bridge. You can use a bridge on a system where some of the links of the system are not bridged and are hence not subject to those constraints.
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Transparent Interconnection of Lots of Links (TRILL)
Oracle Solaris supports the TRILL protection enhancement, which avoids loops without disabling links. TRILL helps to load-balance the traffic between several paths to the destination.
When STP is used for loop protection, the physical loop is mitigated by preventing one of the connections in the loop from forwarding packets. Figure 4–3 shows that the physical link between the westminster and tower bridges is not used to forward packets.
Unlike STP, TRILL does not shut down physical links to prevent loops. Instead, TRILL computes the shortest-path information for each TRILL node in the network and uses that information to forward packets to individual destinations.
You can use TRILL by specifying the –P trill option in the dladm create-bridge or dladm modify-bridge commands. For more information, see Creating a Bridge and Modifying the Protection Type for a Bridge.
For information about STP, see IEEE 802.1D-1998. For information about TRILL, see the Internet Engineering Task Force (IETF) TRILL draft documents.