Cabletron Systems SSIM-R8-02 Especificações descarregar pdf (Página 58)

VLAN Overview

38 Enterasys Xpedition User Reference Manual

Access Ports and Trunk Ports (802.1P and 802.1Q support)

The ports of an XP can be classified into two types, based on VLAN functionality: access

ports and trunk ports. By default, a port is an access port. An access port can belong to at

most one VLAN of the following types: IP, IPX or bridged protocols. The XP can

automatically determine whether a received frame is an IP frame, an IPX frame or neither.

Based on this, it selects a VLAN for the frame. Frames transmitted out of an access port

contain no special information about the VLAN to which they belong. These frames are

classified as belonging to a particular VLAN based on the protocol of the frame and the

VLAN configured on the receiving port for that protocol.

For example, if port 1 belongs to VLAN IPX_VLAN for IPX, VLAN IP_VLAN for IP and

VLAN OTHER_VLAN for any other protocol, then an IP frame received by port 1 is

classified as belonging to VLAN IP_VLAN.

You can use the port enable 8021p command to tag frames transmitted from access ports

with a one-byte, 802.1p class of service (CoS) value. The CoS value indicates the frame’s

priority. There are 8 CoS values, 0 is the lowest priority and 7 is the highest.

Trunk ports (802.1Q) are usually used to connect one VLAN-aware switch to another.

They carry traffic belonging to several VLANs. For example, suppose that XP A and B are

both configured with VLANs V1 and V2.

Then a frame arriving at a port on XP A must be sent to XP B, if the frame belongs to

VLAN V1 or to VLAN V2. Thus the ports on XP A and B which connect the two XPs

together must belong to both VLAN V1 and VLAN V2. Also, when these ports receive a

frame, they must be able to determine whether the frame belongs to V1 or to V2. This is

accomplished by “tagging” the frames, i.e., by prepending information to the frame in

order to identify the VLAN to which the frame belongs. In the XP switching routers, trunk

ports always transmit and receive tagged frames only. The format of the tag is specified by

the IEEE 802.1Q standard. The only exception to this is Spanning Tree Protocol frames,

which are transmitted as untagged frames.

Explicit and Implicit VLANs

As mentioned earlier, VLANs can either be created explicitly by the administrator (explicit

VLANs) or are created implicitly by the XP when L3 interfaces are created (implicit

VLANs).

1 2 ... 53 54 55 56 57 58 59 60 61 62 63 ... 393 394

Sem comentários

Cabletron Systems SSIM-R8-02 Especificações Página 58