Vlan Overview; Vlan Ranges - Cisco 7604 Configuration Manual

Understanding How VLANs Work

VLAN Overview

A VLAN is a group of end stations with a common set of requirements, independent of physical location.
VLANs have the same attributes as a physical LAN but allow you to group end stations even if they are
not located physically on the same LAN segment.
VLANs are usually associated with IP subnetworks. For example, all the end stations in a particular IP
subnet belong to the same VLAN. Traffic between VLANs must be routed. LAN port VLAN
membership is assigned manually on an port-by-port basis.

VLAN Ranges

You must enable the extended system ID to use 4096 VLANs (see the
Note
section on page
Cisco 7600 series routers support 4096 VLANs in accordance with the IEEE 802.1Q standard. These
VLANs are organized into several ranges; you use each range slightly differently. Some of these VLANs
are propagated to other switches in the network when you use the VLAN Trunking Protocol (VTP). The
extended-range VLANs are not propagated, so you must configure extended-range VLANs manually on
each network device.
Table 14-1
Table 14-1 VLAN Ranges
VLANs
0, 4095
1
2–1001
1002–1005 Normal
1006–4094 Extended
The following information applies to VLAN ranges:
•
•
•
•
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
14-2
20-2).
describes the VLAN ranges.
Range Usage
Reserved For system use only. You cannot see or use these VLANs.
Normal Cisco default. You can use this VLAN but you cannot delete it. Yes
Normal For Ethernet VLANs; you can create, use, and delete these
VLANs.
Cisco defaults for FDDI and Token Ring. You cannot delete
VLANs 1002–1005.
For Ethernet VLANs only.
Layer 3 LAN ports, WAN interfaces and subinterfaces, and some software features use internal
VLANs in the extended range. You cannot use an extended range VLAN that has been allocated for
internal use.
To display the VLANs used internally, enter the show vlan internal usage command. With earlier
releases, enter the show vlan internal usage and show cwan vlans commands.
You can configure ascending internal VLAN allocation (from 1006 and up) or descending internal
VLAN allocation (from 4094 and down).
You must enable the extended system ID to use extended range VLANs (see the
Bridge ID" section on page 20-2).
Chapter 14 Configuring VLANs
"Understanding the Bridge ID"
Propagated
by VTP
—
Yes
Yes
No
"Understanding the
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