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716 Appendix A: Answers to the "Do I Know This Already?" Quizzes and Q&A Sections
3
What is the distance limitation of 10BaseT? 100BaseTX?
10BaseT allows 100 meters between the device and the hub or switch, as does
100BaseTX. Table 4-5 on page 144 summarizes the lengths for all Ethernet LAN types.
4
How fast is Fast Ethernet?
100 million bits per second (100 Mbps).
5
What routing protocol does a transparent bridge use to learn about Layer 3 addressing
groupings?
None. Bridges do not use routing protocols. Transparent bridges do not care about Layer
3 address groupings. Devices on either side of a transparent bridge are in the same Layer
3 group--in other words, the same IP subnet or IPX network.
6
Name two of the methods of internal switching on typical switches today. Which provides
less latency for an individual frame?
Store-and-forward, cut-through, and fragment-free. Cut-through has less latency per
frame but does not check for bit errors in the frame, including errors caused by collisions.
Store-and-forward stores the entire received frame, verifies that the FCS is correct, and
then sends the frame. Cut-through sends the first bytes of the frame out before the last
bytes of the incoming frame have been received. Fragment-free is like cut-through, in that
the frame can be sent before the incoming frame is totally received; however, fragment-
free processing waits to receive the first 64 bytes, to ensure no collisions, before beginning
to forward the frame.
7
If a switch hears three different configuration BPDUs from three different neighbors on
three different interfaces, and if all three specify that Bridge 1 is the root, how does it
choose which interface is its root port?
The root port is the port in which the CBPDU with the lowest-cost value is received. The
root port is placed into a forwarding state on each bridge and switch.
8
Assume that a building has 100 devices attached to the same Ethernet. These users then
are migrated onto two separate shared Ethernet segments, each with 50 devices, with a
transparent bridge in between. List two benefits that would be derived for a typical user.
Fewer collisions and less waiting should occur because twice as much capacity exists.
Also, if the placement of devices causes a small percentage of traffic to be forwarded by
the bridge, fewer collisions and less waiting should occur.
9
Define the term broadcast domain.
A set of Ethernet devices for which a broadcast sent by any one of them should be received
by all others in the group. Unlike routers, bridges and switches do not stop the flow of
broadcasts. Two segments separated by a router would each be in a different broadcast
domain. A switch can create multiple broadcast domains by creation of multiple VLANs,
but a router must be used to route packets between the VLANs.
apA.fm Page 716 Monday, March 20, 2000 5:24 PM