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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 15 Configuring VTP
Unders tan ding VTP
•MD5 digest VLAN configuration, including maximum transmission unit (MTU) size for each
VLAN.
•Frame format
VTP advertisements distribute this VLAN information for each configured VLAN:
•VLAN IDs
•VLAN name
•VLAN type
•VLAN state
•Additional VLAN configuration information specific to the VLAN type

VTP Version 2

If you use VTP in your network, you must decide whether to use version 1 or version 2. By default, VTP
operate s in version 1.
VTP version 2 support s these feat ures not supported i n version 1:
•Token Ring support —VTP version 2 su pport s Token Ring Bridg e Relay Fun ction (TrBRF) and
Token Ring Concentrator Relay Function (TrCRF) VLANs. For more information about Token Ring
VLANs, see the “Configuring Normal- Range VL ANs” secti on on page 14-4 .
•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 unre cognized TLV is saved in
NVRAM when the switch is operating in VTP server mode.
•Version-De pende nt Transparent M ode—In VTP version 1, a VTP transparent switch inspects VTP
messages for the domain name a nd version and forwards a message only if the version and domai n
name match. Because V TP version 2 supports onl y one dom ain, it forwar ds VTP messag es in
transparent mode without inspecting the version and domain name.
•Consistency Che cks—In VTP version 2, VLAN co nsistency chec ks (such as VL AN names and
values) are perfo rmed on ly when you enter new informa tion t hrough the CLI, the Cl uster
Managem ent Software (C MS), or SNMP. Consi stency chec ks are not perfo rmed whe n new
information is obtained from a VTP message or when information is read from NVRAM. If the MD5
digest on a received VTP message is correct, its information is accepted.

VTP Pruning

VTP pruning i ncreases network available bandwi dth by restricting floo ded traffic to those tr unk links
that the traffic must use to reach the destination devices. Without VTP pruning, a switch floods
broadcast, multicast, and unknown unicast traffic across all trunk links within a VTP domain even
though re ceiving switches mi ght discar d them. V TP pruning is disabled by default .
VTP pruni ng blocks unn eeded floo ded traffic to VLANs on tr unk ports th at are inc luded in the
pruning -elig ible list. Only VLAN s includ ed in t he pruning -elig ible lis t can be prun ed. By default ,
VLANs 2 t hr ough 1 001 a re p run ing el igibl e sw it ch t ru nk por ts . If t he V LAN s are configur ed as
pruning-ineligible, the flooding continues. VTP pruning is supported with VTP version 1 and version 2.
Figure 15-1 shows a switche d network w ithout VTP pruni n g enabl ed. Port 1 on Sw itch 1 and Port 2 on
Switch 4 are assi gned to the Red VLAN. If a broa dcast is sent fro m the ho st connect ed to Switch 1,
Switch 1 f lood s the broa dca st and every switch in the networ k rece ives it, even thoug h Swi tches 3, 5 ,
and 6 have no ports in the Red VLAN.