Cisco Catalyst 4500 Series, Software Configuration Manual

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 17 Configuring VLANs, VTP, and VMPS
VLAN Trunking Protocol
•
Off—In VTP off mode, a network device functions in the same manner as a VTP transparent device
except that it does not forward VTP advertisements.
Note
Catalyst 4500 series switches automatically change from VTP server mode to VTP client mode if the
switch detects a failure while writing configuration to NVRAM. If this happens, the switch cannot be
returned to VTP server mode until the NVRAM is functioning.
Understanding VTP Advertisements
Each network device in the VTP domain sends periodic advertisements out each trunking LAN interface
to a reserved multicast address. VTP advertisements are received by neighboring network devices, 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)
•
Emulated LAN names (for ATM LANE)
• 802.10 SAID values (FDDI)
•
VTP domain name
• VTP configuration revision number
•
VLAN configuration, including maximum transmission unit (MTU) size for each VLAN
• Frame format
Understanding VTP Versions
VTP Version 2
If you use VTP in your network, you must decide whether to use VTP version 2 or version 3.
Note
Catalyst 4500 series switches do not support Token Ring or FDDI media. The switch does not forward
FDDI, FDDI-Net, Token Ring Concentrator Relay Function (TrCRF), or Token Ring Bridge Relay
Function (TrBRF) traffic, but it does propagate the VLAN configuration by using VTP.
VTP version 2 supports the following features, which are not supported in version 1:
• Token Ring support—Supports Token Ring LAN switching and VLANs (TrBRF and TrCRF).
•
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 and version 2, a VTP transparent network
device 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.