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VTP Versions
VTP comes in two versions: version 1 and version 2. The primary differences between the two version are
few, but they are significant enough to render the two versions incompatible. The two versions will not work
together in the same network. Version 1 is the default on Cisco Catalyst switches and supports Ethernet
media. Version 2 provides the following additional features beyond support for Ethernet:
Consistency checks•
Token Ring support•
Transparent mode change support•
Unrecognized Type Length Value support•
If all the switches in the network support VTP version 2, then only one switch needs to have version 2 enabled
to enable version 2 on all other switches.
Consistency Checks
Consistency checks are performed when new information is entered by an administrator through the command
line interface (CLI) or through Simple Network Management Protocol (SNMP). Normally, no consistency
checks are performed when information for each switch is obtained through a VTP advertising message or
read from nonvolatile RAM (NVRAM). If information is received by an advertisement or read from
NVRAM, a switch will check the MD5 digest on a VTP message; only if it is incorrect will a consistency
check be made.
Token Ring Support
Token−Ring support is provided only in VTP version 2. This support includes Token Ring LAN switching
and VLANs.
Transparent Mode Change Support
In transparent mode, switches will only forward messages and advertisements; the switches will not add any
new information received to its own database. Version 1 allows switches to check the domain name and
version before forwarding. Version 2 allows switches to forward VTP messages and advertisements without
checking the version number.
Unrecognized Type Length Value
If a VTP advertisement is received and has an unrecognized type length value (TLV), the version 2 VTP
switches will still propagate the changes through their trunk links. A VTP server or client propagates its
configuration changes to the configured trunk links, even for TLVs it is not able to parse. The unrecognized
TLV is then saved in NVRAM.
VTP Advertisements
Switches in a VTP management domain share VLAN information through VTP advertisement messages.
There are three types of advertisement messages:
Advertisement request—Occurs when clients request VLAN information for the current network. A
VTP sends these types of advertisements in response to requests with the appropriate summary and
subset advertisements. The advertisement frame includes a version field, code field, reserved field,
management domain name field (up to 32 bytes), and start value field.
•
Summary advertisement—Sent automatically every 5 minutes (300 seconds) to all the switches on the
network. A summary advertisement can also be sent when a topology change occurs on the network,
such as a switch drop or addition. The summary advertisement frame contains the version field, the
code field, a followers field, a management domain name field, a configuration revision number field,
•
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