Cabletron Systems SSIM-R8-02 Specifikace stáhnout pdf (Strana 54)

VLAN Overview

34 Enterasys Xpedition User Reference Manual

Address-based bridging - The XP performs this type of bridging by looking up the

destination address in an L2 lookup table on the line card that receives the bridge packet

from the network. The L2 lookup table indicates the exit port(s) for the bridged packet. If

the packet is addressed to the XP’s own MAC address, the packet is routed rather than

bridged.

Flow-based bridging - The XP performs this type of bridging by looking up an entry in

the L2 lookup table containing both the source and destination addresses of the received

packet in order to determine how the packet is to be handled.

The XP ports perform address-based bridging by default but can be configured to perform

flow-based bridging instead, on a per-port basis. A port cannot be configured to perform

both types of bridging at the same time.

The XP performance is equivalent when performing flow-based bridging or address-

based bridging. However, address-based bridging is more efficient because it requires

fewer table entries while flow-based bridging provides tighter management and control

over bridged traffic.

VLAN Overview

Virtual LANs (VLANs) are a means of dividing a physical network into several logical

(virtual) LANs. The division can be done on the basis of various criteria, giving rise to

different types of VLANs. For example, the simplest type of VLAN is the port-based

VLAN. Port-based VLANs divide a network into a number of VLANs by assigning a

VLAN to each port of a switching device. Then, any traffic received on a given port of a

switch belongs to the VLAN associated with that port.

VLANs are primarily used for broadcast containment. A layer-2 (L2) broadcast frame is

normally transmitted all over a bridged network. By dividing the network into VLANs,

the range of a broadcast is limited, i.e., the broadcast frame is transmitted only to the

VLAN to which it belongs. This reduces the broadcast traffic on a network by an

appreciable factor.

The type of VLAN depends upon one criterion: how a received frame is classified as

belonging to a particular VLAN. VLANs can be categorized into the following types:

• Port based

• MAC address based

• Protocol based

• Subnet based

• Multicast based

• Policy based

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 393 394

Žádné komentáře

Cabletron Systems SSIM-R8-02 Specifikace Strana 54