GE T1000, Техническое руководство

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GE Reason Switches Chapter 4
– Functions
REASON SWITCHES-TM-EN-3 57
multicast frames must be delivered to all ports, except the incoming port. In the
example given, switch A will send the multicast to switch B through all ports.
Switch B will execute the switch algorithm and will send the multicast frame to all
ports, except the incoming frame port. Thus, the multicast received in one port will be
replicated to the other connected port, and so on. Since Layer 2 header does not
support a time to live (TTL), every multicast frame will be endless replicated until there
is resource exhaustion or a crash happens in the network.
Finally, MAC address table will not converge the actual topology, as the Sender and
Receiver port will continuously change. If the Sender starts a communication with the
Receiver, switch A and B will view initially that the position of the Receiver is one port,
and then another. This behavior will make the switch continuously recalculate its
MAC addresses table, leading to traffic loss.
Redundancy might be a requirement in networks. The redundant path is possible due
to the usage of redundancy or loop resolution protocols. For loop resolution, the most
common is Spanning Tree protocols, and for link redundancy the Link Aggregation
protocol.
5.2 Loop Protection
Reason Switches support detection and protection from a network loop in two ways,
using spanning tree protocols or using the Loop Protection function. This section
shows the Loop Protection function. Refer to next section for spanning tree protocol
description.
The Loop Protection function is used to prevent loops between a port and another at
the same switch or at ports connected to unmanaged switches. Unmanaged
switches could drop spanning tree packets, thus interfering in its operation. To
prevent problems caused by these situations, the Loop Protection function must be
enabled at ports where the loop could happen. Examples of these connections are
shown in figure 14 below.
Figure 14: Usage situations for Loop Protection
The function is executed by sending messages throughout the ports that are enabled
to send loop detection protocol. If a port that has been enabled to send loop
detection packet receives it, this port will be shutdown, as it will detect a loop in this
port.