Switching Topic 3 VTP

Agenda VTP basics Components Frames and advertisements Domains and revision numbers VTP operations VTP pruning VTP issues

VTP basics VLAN Trunking Protocol Sends VLAN information to other switches in the network Makes VLAN configuration changes on the switch with the VTP server role VTP advertisements distribute and sync VLAN changes to other switches Layer 2 protocol, Cisco® proprietary protocol

VTP benefits Less work! Do it once on the VTP server and let it propagate Easy VLAN management on switches – Adding, deleting and renaming VLANs Configurations are consistent and have less errors Dynamic reporting of new VLANs Dynamic trunk configuration when new VLANs are added

VTP components VTP domain (the scope) – The switches that accept advertisements and are updated by VTP VTP advertisements – Messages that distribute and synchronise VLAN configurations over trunk links VTP switch modes – VTP Server: Make VLAN changes on the VTP server, VLAN list for domain stored in NVRAM – VTP client: Receives VLAN information from VTP server advertisements, VLAN list stored in RAM (lost when powered off) – VTP transparent: Relays VTP advertisements to VTP clients and VTP servers Does not accept VLAN information VLANs can be configured manually and are local to the switch

VTP frame VTP header and message inserted into data field of an Ethernet frame Frame is tagged as 802.1q frame – EtherType and tag control field inserted behind source MAC address field

VTP advertisements Summary advertisements – Sent every five mins by client and server switches to advertise their current revision number – Sent after a configuration change Subset advertisement – Sent if a change in the VLAN configuration is made – Sent in response to an advertisement request – may be multiple messages Advertisement request – Sent to a VTP server to request new information – Sent when: When VTP domain name changes When an advertisement with a higher revision number is received Subset advertisement is missed Switch is reset

VTP frame details Summary advertisement contains VTP domain name Updater identity and timestamp MD5 digest (for integrity) Configuration revision number Subset advertisement contains VTP domain name Configuration revision number VLAN ID VLAN name VLAN type VLAN status Additional information

VTP domains Large networks are divided into smaller VTP management domains A VTP domain is one or more connected switches with the same VTP domain name (case sensitive) A switch can be a member of only one VTP domain at a time VTP advertisements are only accepted from switches in the same VTP domain (dropped if different domain) Each switch (server and client) in the domain sends advertisements out each trunk port to a reserved multicast address ( C-CC-CC-CC) every five minutes – Advertisements are received by neighbouring switches, which update their VTP and VLAN configurations as necessary – Currency of information is controlled by the configuration revision number

Configuration revision number Determines which advertisement has the most recent information 32 bit number in the VTP header of summary advertisements Default is zero, each time a VLAN is added, removed or renamed the number is incremented Configuration revision number reset to zero if: – A VTP domain name change – Changing a switch mode to transparent – Switch is reset

Default VTP configuration settings VTP version = 1 VTP domain name = null VTP mode = Server Config revision = 0 VLANs = 1 (referring to VLAN 1) Version 2 supports token ring messages VTP password is used for the integrity check – If used the same password must be configured on all switches in the domain

VTP operations Configure VTP domain name on VTP server (must be done before adding VLANs) Configure new VLANs – Configuration revision number will increment with each change Bring up trunk links, VTP only works over dot1q, ISL and LANE LAN emulation trunk links – VTP Server sends summary advertisement to connected switches – Switches update the VTP domain name from NULL (the default) – Summary advertisement arrives at neighbour switch with a higher revision number Neighbour switches sends advertisement request – VTP server responds with a 2 nd summary advertisement followed by subset advertisements Switches update VLAN configurations and configuration revision number VTP transparent mode switches forward advertisements along trunk links but make no updates to their VLAN information VTP servers and clients continue sending summary advertisements (5 mins)

VTP pruning Normally VTP messages are sent to every switch in the domain down all trunk links VTP pruning prevents unnecessary flooding of VTP information If VLANs have no switchports on downstream switches, VTP messages are not sent VLANs can be marked as pruning-eligible and VTP reconfigures the trunk links to prune VTP messages on the egress port Pruning is disabled by default – enable pruning on only one VTP server switch in the domain

Troubleshooting Incompatible VTP versions – VTP versions 1 and 2 are incompatible VTP password issues – No password set or password misconfigured – Password must be set manually on each switch Incorrect VTP domain name – Set the VTP domain name on one VTP server switch to avoid incorrect configuration – Case sensitive All switches set to VTP client mode – Configure a VTP server and a backup VTP server switch

VTP issues Inserting a switch (VTP server or a client) with higher VTP configuration revision number – Switches will update VLANs to those of the new switch, loss of connectivity – Add back the required VLANs and delete the unwanted VLANs on a VTP server – Change VTP mode to transparent or change the domain name to reset the revision number Inserting a switch with a different domain name between switches – Trunk links may drop, VTP domain mismatch and no VTP updates will occur – Trunk link must be set to ON on both sides of link Trunks set to desirable or any other settings will not form a trunk if the domains are different – All switches in the domain must be adjacent and connected by trunks Messages will not be relayed over different VTP domains (dropped) – Change the VTP domain name to solve

Agenda VTP basics Components Frames and advertisements Domains and revision numbers VTP operations VTP pruning VTP issues

Switching Topic 3 VTP