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Chapter 3
VLANs
Before inserting a switch, make sure that you follow these thee steps:
1.
Perform a clear config all to remove any existing VLAN config-
uration on a set-based switch. On the 1900, use the delete NVRAM
command.
2.
Power-cycle the switch to clear the VTP NVRAM.
3.
Configure the switch to perform the mode of VTP that it will partici-
pate in. Cisco's rule of thumb is that you create several VTP servers in
the domain, with all the other switches set to client mode.
VTP Pruning
To preserve bandwidth, you can configure the VTP to reduce the amount of
broadcasts, multicasts, and other unicast packets. This is called VTP prun-
ing. VTP restricts broadcasts to only trunk links that must have the informa-
tion. If a trunk link does not need the broadcasts, the information is not sent.
VTP pruning is disabled by default on all switches.
For example, if a switch does not have any ports configured for VLAN 5
and a broadcast is sent throughout VLAN 5, the broadcast would not
traverse the trunk link going to the switch without any VLAN 5 members.
Enabling pruning on a VTP server enables pruning for the entire domain,
and by default, VLANs 2 through 1005 are eligible for pruning. VLAN 1 can
never prune.
Use the following command to set VLANs to be eligible for pruning:
Console> (enable) set vtp pruneeligible ?
Usage: set vtp [domain <name>] [mode <mode>]
[passwd <passwd>] [pruning <enable|disable>]
[v2 <enable|disable> (mode = client|server|transparent
Use passwd '0' to clear vtp password)
Usage: set vtp pruneeligible <vlans>
(vlans = 2..1000
An example of vlans is 2-10,1000)
Console> (enable) set vtp pruneeligible 2
Vlans 2-1000 eligible for pruning on this device.
VTP domain Globalnet modified.
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