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FTOS Configuration Guide for the C-Series - Force10 Networks

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When a double-tagged packet enters a trunk port in a service provider core switch, <strong>the</strong> outer tag is stripped<br />

as <strong>the</strong> switch processes <strong>the</strong> packet. When <strong>the</strong> packet exits ano<strong>the</strong>r trunk port on that switch, <strong>the</strong> same outer<br />

tag is added back to <strong>the</strong> packet. Any required FCS re-computation is per<strong>for</strong>med as usual.<br />

A VLAN-Stack tag (with a different protocol type) and a new CRC is inserted in every frame at <strong>the</strong> ingress<br />

edge device. These are removed at <strong>the</strong> egress edge device, and <strong>the</strong> original VLAN tagging is preserved.<br />

While <strong>the</strong> intermediate devices treat <strong>the</strong> frame as a regular E<strong>the</strong>rnet frame, <strong>the</strong> insertion of a VLAN-Stack<br />

tag increases <strong>the</strong> maximum frame size by 4 bytes, making it a Baby Giant frame.<br />

Figure 138 illustrates where <strong>the</strong> VLAN-stack tag is added (after <strong>the</strong> Source Address and be<strong>for</strong>e <strong>the</strong> VLAN<br />

ID tag). The first part of <strong>the</strong> tag is <strong>the</strong> user-configurable protocol type value (default 0x9100) and <strong>the</strong><br />

second part is <strong>the</strong> VLAN ID you assign to <strong>the</strong> VLAN-Stack (0007 in this example).<br />

Figure 138 Location of VLAN-Stack Tag in Packet Header<br />

Implementation In<strong>for</strong>mation<br />

The VLAN-Stack tag uses a configurable protocol type (Etype). The default is 0x9100, but you can set it to<br />

any value. Intermediate devices in a VLAN-Stack network recognize this protocol type and switch packets<br />

based on it.<br />

To create a VLAN-Stack network, you must designate its interfaces as ei<strong>the</strong>r VLAN-Stack access ports or<br />

VLAN-Stack trunk ports, and assign <strong>the</strong>se interfaces to a VLAN-Stack-enabled VLAN.<br />

The following interface types can be VLAN-Stack access or trunk ports:<br />

• E<strong>the</strong>rnet ports (Gigabit E<strong>the</strong>rnet and 10 Gigabit E<strong>the</strong>rnet)<br />

• Port Channels (LAGs)<br />

DA SA 0x9200 0007 0x8100 0005<br />

VLAN-Stack Tag VLAN ID<br />

(Service Provider Tag) (Customer Tag)<br />

Important Points to Remember (Basic VLAN-Stacking)<br />

• 1-GE and 10-GE physical interfaces and port-channel interfaces can be configured as VLAN-Stack<br />

access or trunk ports.<br />

• Interfaces that are members of <strong>the</strong> Default VLAN and are configured as VLAN-Stack access or trunk<br />

ports do not switch untagged traffic. These interfaces must be added to a non-default<br />

VLAN-Stack-enabled VLAN to switch traffic.<br />

• You can assign an IP address to a VLAN-Stack VLAN only if all member interfaces are VLAN-Stack<br />

trunk ports. A VLAN-Stack VLAN cannot be assigned an IP address if <strong>the</strong> VLAN contains<br />

VLAN-Stack access ports. This facility is provided <strong>for</strong> SNMP management over a<br />

VLAN-Stack-enabled VLAN containing only VLAN-Stack trunk interfaces. Layer 3 routing protocols<br />

on such a VLAN are not supported.<br />

• <strong>Force10</strong> cautions against using <strong>the</strong> same MAC address on different customer VLANs, on <strong>the</strong> same<br />

VLAN-Stack VLAN.<br />

228 VLAN Stacking<br />

fn00091a

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