Cisco Systems WSC2960XR48FPSI Normal-Range VLAN Configuration Guidelines

Normal-Range VLAN Configuration Guidelines

Normal-rangeVLANs are VLANs with IDs from 1 to 1005. VTP 1 and 2 only support normal-range VLANs.

Followthese guidelines when creatingand modifying normal-rangeVLANs in yournetwork:

•Normal-rangeVLANs are identified with a number between 1 and 1001. VLAN numbers 1002 through

1005are reservedfor Token Ring and FDDI VLANs.

•VLANconfiguration for VLANs 1 to 1005 are alwayssaved in the VLAN database. If the VTP mode

istransparent, VTP andVLAN configurationare also saved inthe switch runningconfiguration file.

•Ifthe switch is in VTP server or VTP transparent mode, you can add, modify or remove configurations

forVLANs 2 to 1001 in the VLAN database. (VLAN IDs 1 and 1002 to 1005 are automatically created

andcannot be removed.)

•WithVTP versions 1 and 2, the switch supports VLAN IDs 1006 through 4094 only in VTP transparent

mode(VTP disabled). These are extended-range VLANs and configuration options are limited.

Extended-rangeVLANs created in VTP transparent mode are not saved in the VLAN database and are

notpropagated. VTP version 3 supports extended range VLAN (VLANs 1006 to 4094) database

propagationin VTP server and transparent mode. If extended VLANs are configured, you cannot convert

fromVTP version 3 to version 1 or 2.

•Beforeyou can create a VLAN, the switch must be in VTP server mode or VTP transparentmode. If

theswitch is a VTP server, you must define a VTP domain or VTP will not function.

•Theswitch does not support Token Ring or FDDI media. The switch does not forward FDDI, FDDI-Net,

TrCRF,or TrBRF traffic, but it does propagate the VLAN configuration through VTP.

•Theswitch supports 128 spanningtree instances. If aswitch has moreactive VLANs than supported

spanning-treeinstances, spanning tree can be enabled on 128 VLANs and is disabled on the remaining

VLANs.If you have already used all available spanning-tree instances on a switch, adding another

VLANanywhere in theVTP domain creates a VLAN on thatswitch that is not runningspanning-tree.

Ifyou have the default allowed list on the trunk portsof that switch (which is to allow all VLANs), the

newVLAN is carriedon all trunk ports. Depending on the topology of thenetwork, this could create a

loopin the new VLAN that would not be broken, particularly if there are several adjacent switches that

allhave run out ofspanning-tree instances. You can prevent this possibility by setting allowed lists on

thetrunk ports of switches that have used up their allocation of spanning-tree instances.

Ifthe number of VLANson theswitch exceeds the number of supported spanning-tree instances, we

recommendthat you configure the IEEE 802.1s Multiple STP (MSTP) on your switch to map multiple

VLANsto asingle spanning-tree instance.

•Whena switch in a stack learns a new VLAN or deletes or modifies an existing VLAN (either through

VTPover network ports orthrough theCLI), the VLAN information is communicated to all stack

members.

•Whena switch joins a stack or when stacks merge, VTP information (the vlan.dat file) on the new

switcheswill be consistentwith the active switch.