Data
forwarding can be impaired when the switch consumes the resources that are coping
with instability in the MAC address table.
Layer 2 LAN protocols, such as Ethernet, lack a mechanism to recognize and eliminate
endlessly looping frames. Some Layer 3 protocols like IP implement a Time-To-Live (TTL)
mechanism that limits the number of times a Layer 3 networking device can retransmit a
packet. Lacking such a mechanism, Layer 2 devices continue to retransmit looping traf?¬?c
inde?¬?nitely.
A loop-avoidance mechanism is required to solve each of these problems.
Server/Host X Router Y
Segment 1
Segment 2
46 Chapter 2: Medium-Sized Switched Network Construction
Recognizing Issues of a Redundant Switched Topology
Because of the simple algorithms that a Layer 2 device uses to forward frames, numerous
issues must be managed in a redundant topology. Although these issues are managed with
technology built into the devices, a failure in these technologies may create network
outages. It is important to understand these issues in more detail.
Switch Behavior with Broadcast Frames
Switches handle broadcast and multicast frames differently from the way they handle
unicast frames.
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