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CCNA Cisco Certified Network Associate Study Guide - FTP Server

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312 Chapter 6 � Virtual LANs (VLANs)<br />

Configuration Revision Number<br />

The revision number is the most important piece in the VTP advertisement.<br />

Figure 6.5 shows an example of how a revision number is used in an<br />

advertisement.<br />

FIGURE 6.5 VTP revision number<br />

VTP Pruning<br />

4. N+1<br />

5. Sync new VLAN info<br />

3<br />

<strong>Server</strong><br />

1. Add new VLAN<br />

2. N+1<br />

Client Client<br />

VTP advertisements are sent every five<br />

minutes or whenever there is a change.<br />

4. N+1<br />

5. Sync new VLAN info<br />

This figure shows a configuration revision number as “N.” As a database<br />

is modified, the VTP server increments the revision number by 1. The VTP<br />

server then advertises the database with the new configuration revision number.<br />

When a switch receives an advertisement that has a higher revision number,<br />

it overwrites the database in NVRAM with the new database being<br />

advertised.<br />

You can preserve bandwidth by configuring the VTP to reduce the amount<br />

of broadcasts, multicasts, and other unicast packets, which helps preserve<br />

bandwidth. This is called pruning. VTP pruning only sends broadcasts to<br />

trunk links that must have the information; any trunk link that does not need<br />

the broadcasts will not receive them. For example, if a switch does not have<br />

any ports configured for VLAN 5, and a broadcast is sent throughout VLAN 5,<br />

the broadcast would not traverse the trunk link to this switch. VTP pruning<br />

is disabled by default on all switches.<br />

3

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