D-Link DES-3326 User Manual - Segmenting Broadcast Domains
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
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Switch Management and Operating Concepts
Broadcast storms have long been a concern for network
administrators with routers traditionally being used to prevent
their occurrence, and if that failed, limit their scope. However, with
the advent of VLANs, switches are now able to limit broadcast
domains better and cheaper than routers. Also, many switches,
including the DES-3226, have broadcast sensors and filters built
into each port to further control broadcast storms.
Segmenting Broadcast Domains
VLANs can be used to segment broadcast domains. They do this by
forwarding packets only to ports that are members of the same
VLAN. Other parts of the network are effectively shielded. Thus,
the smaller the broadcast domain, the smaller effect a broadcast
storm will have. Because VLANs are implemented at each switch
port, they can be quite effective in limiting the scope of broadcast
storms.
Eliminating Broadcast Storms
SNMP agents can be programmed to monitor the number of
broadcast packets on switch ports and act on the data. When the
number of broadcast packets on a given port rise past an assigned
threshold, an action can be triggered. When enabled, the usual
action is to block the port from receiving broadcast packets. This
will discard all broadcast frames arriving at the port from the
attached segment. Not only does this isolate the broadcast domain,
but it actually starts removing broadcast packets from the affected
segment. When the number of broadcast packets falls to an
acceptable level (below the trigger level), the SNMP agent can
remove the blocking condition, returning the port to its normal
operational state.
In the DES-3326, the default trigger threshold is set to 128,000
broadcast packets per second (128 Kpps) for both 100 Mbps Fast
Ethernet ports and the optional 1000 Mbps Gigabit Ethernet ports.