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What are different characteristics of VTP (Virtual Trunk Protocol)?

– VTP (virtual trunk protocol) or VLAN trunking protocol was developed by the Cisco Systems as a proprietary protocol. – This protocol was developed with the purpose of propagating the VLAN (virtual local area network) definition to whole physical LAN.
– For achieving this, VLAN information is carried by this protocol to all the switches over a VTP domain.
– Using the below mentioned trunks, the VTP advertisements can be sent:
1. ISL
2. 802.1q
3. IEEE 802.10
4. LANE

Characteristics of Virtual Trunk Protocol

1. Its first characteristic is its ability to update all the switches with new data or info automatically in a VLAN network and thus ensures that all the switches are set as per the VLAN topology and are up to date.
2. Whenever a VLAN is configured on a VTP server, VTP automatically distributes it to the switches all over the domain. Because of this you don’t need to configure the VLAN at every point.
3. VTP makes use of IEEE 802.1Q frames or ISL (inter – switched link) frames for sending its packets.
4. VTP packets have a unique format: They are delivered to the destination address along with LLC (logical link control) code of SNAP (sub – network access protocol) and a SNAP header. All this is encapsulated in an ISL frame. When VTP packet is encapsulated in 802.1Q frames, the case is different. Here, dot1q tagging replaces the CRC (cyclic redundancy check) and the ISL header.
5. Varying format: VTP packet varies its format depending up on the type of its message. But, all packets do contain the following fields in their frame header:
– The protocol version
– The message type: it can be a subset advertisement, summary advertisement, VTP join messages or an advertisement request.
– Management domain name
– Management domain length

6. Configuration revision number: It’s a 32 – bit number indicating the revision level for a packet. This number is tracked by every VTP device and is assigned to them. It helps in determining whether the received information is latest or not. Each time a change is made in the device; this number is increased by one. For resetting the configuration revision number, the VTP domain name should be changed to some other and should be changed again back to the original one.
7. VTP modes: It offers a number of modes:
– Server mode: VLANs can be created, modified or deleted and there other configuration parameters can be specified.
– Client mode: The behavior of VTP servers and clients is almost same, but on a VTP client, VLANs cannot be created, modified or deleted.
– Transparent mode: It uses the transparent switches for forwarding the VTP advertisements to their trunk ports in lower VTP versions.
– Off mode: The VTP behavior in this mode is similar to the VTP transparent mode but here the exception is that the advertisements are not forwarded whereas in other modes, the advertisements are forwarded as soon as they are received.
8. VTP password: You can set a password for VTP provided that you set password for all the switches in its domain. All should have the same password. This password is translated in to a 16 – byte word and is carried in all VTP packets.
9. VTP pruning: It is ensured by VTP that all switches known about all the VLANs. But in certain situations, unnecessary traffic can be created i.e., the entire VLAN can get flooded by all sorts of unknown broadcasts and unicasts. All broadcasts are received by all the switches. This pruning feature lets you prune or eliminate this unnecessary traffic.

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