Cisco WS-C2960-24PC-L Software Guide - Page 179
Understanding VTP Advertisements, Version-Dependent Transparent Mode-In VTP version 1
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Chapter 9 Configuring VTP Understanding How VTP Version 1 and Version 2 Work • Transparent-VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, transparent switches do forward VTP advertisements that they receive out their trunk ports. • Off-In the three modes described above, VTP advertisements are received and transmitted as soon as the switch enters the management domain state. In the VTP off mode, switches behave the same as in VTP transparent mode with the exception that VTP advertisements are not forwarded. Understanding VTP Advertisements Each switch in the VTP domain sends periodic advertisements out each trunk port to a reserved multicast address. VTP advertisements are received by neighboring switches, which update their VTP and VLAN configurations as necessary. The following global configuration information is distributed in VTP advertisements: • VLAN IDs (ISL and 802.1Q) • VTP domain name • VTP configuration revision number • VLAN configuration, including the maximum transmission unit (MTU) size for each VLAN • Frame format Understanding VTP Version 2 If you use VTP in your network, you must decide whether to use VTP version 1, version 2, or version 3 (for details on version 3, see the "Understanding How VTP Version 3 Works" section on page 9-13). VTP version 2 supports the following features that are not supported in version 1: • Unrecognized Type-Length-Value (TLV) Support-A VTP server or client propagates configuration changes to its other trunks even for TLVs it is not able to parse. The unrecognized TLV is saved in NVRAM. • Version-Dependent Transparent Mode-In VTP version 1, a VTP transparent switch inspects VTP messages for the domain name and version and forwards a message only if the version and domain name match. Since only one domain is supported in the supervisor engine software, VTP version 2 forwards VTP messages in transparent mode without checking the version. • Consistency Checks-In VTP version 2, VLAN consistency checks (such as VLAN names and values) are performed only when you enter new information through the CLI or SNMP. Consistency checks are not performed when new information is obtained from a VTP message, or when information is read from NVRAM. If the digest on a received VTP message is correct, its information is accepted without consistency checks. 78-15486-01 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 9-3