Transcript Switching

Switching
Topic 3
VTP
Agenda
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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:
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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
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VTP domain name
Updater identity and timestamp
MD5 digest (for integrity)
Configuration revision number
• Subset advertisement contains
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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 (01-00-0C-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
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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 2nd 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
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VTP basics
Components
Frames and advertisements
Domains and revision numbers
VTP operations
VTP pruning
VTP issues
Switching
Topic 3
VTP