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FTOS Configuration Guide for the C-Series - Force10 Networks

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VLANs and Port Tagging<br />

To add an interface to a VLAN, it must be in Layer 2 mode. After you place an interface in Layer 2 mode,<br />

it is automatically placed in <strong>the</strong> Default VLAN. <strong>FTOS</strong> supports IEEE 802.1Q tagging at <strong>the</strong> interface level<br />

to filter traffic. When tagging is enabled, a tag header is added to <strong>the</strong> frame after <strong>the</strong> destination and source<br />

MAC addresses. That in<strong>for</strong>mation is preserved as <strong>the</strong> frame moves through <strong>the</strong> network. Figure 92<br />

illustrates <strong>the</strong> structure of a frame with a tag header. The VLAN ID is inserted in <strong>the</strong> tag header.<br />

E<strong>the</strong>rnet<br />

Preamble Destination<br />

Address<br />

Figure 92 Tagged Frame Format<br />

Source<br />

Address<br />

6 octets 6 octets<br />

The tag header contains some key in<strong>for</strong>mation used by <strong>FTOS</strong>:<br />

• The VLAN protocol identifier identifies <strong>the</strong> frame as tagged according to <strong>the</strong> IEEE 802.1Q<br />

specifications (2 bytes).<br />

• Tag Control In<strong>for</strong>mation (TCI) includes <strong>the</strong> VLAN ID (2 bytes total). The VLAN ID can have 4,096<br />

values, but 2 are reserved.<br />

Note: The insertion of <strong>the</strong> tag header into <strong>the</strong> E<strong>the</strong>rnet frame increases <strong>the</strong> size of <strong>the</strong> frame to more than<br />

<strong>the</strong> 1518 bytes specified in <strong>the</strong> IEEE 802.3 standard. Some devices that are not compliant with IEEE 802.3<br />

may not support <strong>the</strong> larger frame size.<br />

In<strong>for</strong>mation contained in <strong>the</strong> tag header allows <strong>the</strong> system to prioritize traffic and to <strong>for</strong>ward in<strong>for</strong>mation to<br />

ports associated with a specific VLAN ID. Tagged interfaces can belong to multiple VLANs, while<br />

untagged interfaces can belong only to one VLAN.<br />

<strong>Configuration</strong> Task List <strong>for</strong> VLANs<br />

This section contains <strong>the</strong> following VLAN configuration tasks:<br />

• Creating a port-based VLAN on page 184 (mandatory)<br />

• Assigning interfaces to a VLAN on page 185 (optional)<br />

• Assigning an IP address to a VLAN on page 188 (optional)<br />

Creating a port-based VLAN<br />

Tag<br />

Header<br />

Protocol<br />

Type<br />

The Default VLAN as VLAN 1 is part of <strong>the</strong> system startup configuration and does not require<br />

configuration. To configure a port-based VLAN, you must create <strong>the</strong> VLAN and <strong>the</strong>n add physical<br />

interfaces or port channel (LAG) interfaces to <strong>the</strong> VLAN.<br />

184 Layer 2<br />

Data<br />

Frame<br />

Check<br />

Sequence<br />

4 octets 2 octets 45 - 1500 octets 4 octets<br />

FN00001B

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