Chapter 7 Switch Configuration
7.1 Introduction
Some of our routers have an internally-connected switch to an Ethernet interface.
A switch enables traffic separation through the creation of independent segments. To do this, the switch has several
ports (each one corresponding to a segment). The switch learns the MAC addresses in each segment and only al-
lows traffic to pass from one segment to another when the destination address is proven to belong to another seg-
ment or is a group address (multicast or broadcast).
7.2 Traffic Storm Control
A switch transmits the broadcast and multicast traffic received through a port to the remaining ports. Similarly, if a
destination MAC address for a unicast packet isn’t known to the switch, the packet is sent through all ports. If high
volumes of this type of traffic are generated (traffic storms) in a segment, they are sent to all segments. Traffic
storms usually stem from network configuration errors and can saturate the network.
Using the traffic storm control frame throughput at the switch port can be limited.
Traffic control is configured by entering storm-control. Traffic control is a characteristic of the switch being used (i.e.
it's a hardware characteristic, not software-related), meaning its configuration varies depending on the switch being
used in the device.
The configurable parameters are as follows:
• Bandwidth, which triggers the traffic control mechanism. If the number of frames of a certain type received by a
port surpasses the bandwidth configured for said port, the switch stops sending these frames to the other ports.
• The type of frames to take into account when the traffic control mechanism begins to operate: all frames, broadcast
frames, multicast frames or flooded-unicast (unicast frames sent by all the switch ports when the destination ad-
dress cannot be found in the switch’s MAC addressing table).
• Traffic control mechanism, enabled or disabled in the switch port.
Depending on the type of switch, the first two parameters can be configured globally or per port. The types of frames
that can be taken into account for traffic control also vary according to the type of switch used.
If you enable traffic control in a port, the switch calculates, in time intervals, the number of frames received for the
configured types. If the number of frames surpasses the configured bandwidth, the frame reception process is
stopped in said port until the next time interval for calculation begins. The frame counter restarts when a new calcula-
tion period begins.
When configuring traffic control, please remember hardware limitations may be set in the bandwidth values of the
switch (i.e., little resolution in the internal registers used). This means that, in some switches, the real value of the
bandwidth used is different from the value configured. You can view the real value in the switch by entering list
storm-control (a monitoring command).
7.3 Spanning Tree Protocol
You can configure three different switch ports to execute the Spanning Tree protocol. Ports can be divided in differ-
ent Spanning Tree instances.
Note
Throughout this manual, the ports grouped in a Spanning Tree instance are sometimes referred to as
bridge
.
When enabling Spanning Tree in a switch port, take the following considerations into account:
• The switch for the BPDU frames stops executing regardless of whether the frame is received through a port where
Spanning Tree is running or not.
• You cannot configure
bridge
in a switch where a port is running Spanning Tree.
• You cannot configure a port as a
WAN port
if a Spanning Tree is running. For further information on
WAN ports
,
please see manual
Teldat Dm750-I Ethernet Subinterface
.
Teldat SA
7 Switch Configuration
LAN Interfaces
41
