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发布时间：2006-06-28 04:58     点击：

41) Describe LAN segmentation using bridges.

Bridges segment LANs by using MAC addresses. MAC Address learning is a service that characterises a learning bridge, in which the source MAC address of each received packet is stored is so that future packets destined for that address can be forwarded only to the bridge interface on which that address is located. Packets destined for unrecognised addresses are forwarded out every bridge interface. This scheme helps minimise traffic on the attached LANs. MAC address learning is defined in the IEEE 802.1 standard.

42) Describe LAN segmentation using routers.

LAN segmentation using routers is simply a router between Lans. Broadcast messages are not forwarded across routed segments. LAN segmentation is done at layer 3 (Network layer) unlike bridging which is done at layer 2 (Data Link Layer).

43) Describe LAN segmentation using switches.

Switch segments are basically are highly intelligent bridged segments, with a few other interesting features such as VLANs (Virtual Local Area Networks), and lots of protocols for tunnelling data between switches. Switches provide the same functionality as bridges except they do it at a wire speed (without introducing latency).

44) Name and describe two switching methods.

Store-and-forward Switching Method

Store-and-forward switching is one of the two main types of LAN switching.

With the store-and-forward switching method, the LAN switch copies the entire flame into its onboard buffers and computes the cyclic redundancy check (CRC).

The frame is discarded if it contains a CRC error, or if it is a runt (less than 64 bytes including the CRC), or a giant (more than 1518 bytes including the CRC).

If the frame does not contain any errors, the LAN switch looks up the destination address in its forwarding or switching, table and determines the outgoing interface. It then forwards the frame toward its destination.

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