Cisco 2950 Software Configuration Guide - Page 398
VTP Version 2, VTP Pruning
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Understanding VTP Chapter 18 Configuring 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 operates in version 1. VTP version 2 supports these features not supported in version 1: • Token Ring support-VTP version 2 supports Token Ring Bridge Relay Function (TrBRF) and Token Ring Concentrator Relay Function (TrCRF) VLANs. For more information about Token Ring VLANs, see the "Configuring Normal-Range VLANs" section on page 17-4. • 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 unrecognized TLV is saved in NVRAM when the switch is operating in VTP server mode. • 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. Because VTP version 2 supports only one domain, it forwards VTP messages in transparent mode without inspecting the version and domain name. • 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, the Cluster Management Software (CMS), 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 MD5 digest on a received VTP message is correct, its information is accepted. VTP Pruning VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk 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 receiving switches might discard them. VTP pruning is disabled by default. VTP pruning blocks unneeded flooded traffic to VLANs on trunk ports that are included in the pruning-eligible list. Only VLANs included in the pruning-eligible list can be pruned. By default, VLANs 2 through 1001 are pruning eligible switch trunk ports. If the VLANs are configured as pruning-ineligible, the flooding continues. VTP pruning is supported with VTP version 1 and version 2. Figure 18-1 shows a switched network without VTP pruning enabled. Port 1 on Switch A and Port 2 on Switch D are assigned to the Red VLAN. If a broadcast is sent from the host connected to Switch A, Switch A floods the broadcast and every switch in the network receives it, even though Switches C, E, and F have no ports in the Red VLAN. 18-4 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 78-11380-10