Vlan Interview Questions and Answers

Vlan Interview Questions and Answers

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Which switching technology reduces the size of a broadcast domain?

Which protocols are used to configure trunking on a switch?

What is SVI ?
Switched Virtual Interface (SVI) is a virtual interface which provides a routed gateway into and out of a VLAN

what is meant by "router on stick" ?
Router on  Stick is a method used for communicating Inter-VLAN's  using a router

which is the default mode in switch ports ?
Older switches are dynamic desirable by default and modern switches are dynamic auto by default

Difference between 802.1Q and ISL ?
Cisco ISL (Inter-Switch Link) is an old Cisco proprietary protocol that is only supported on some Cisco switches. While 802.1Q [dot1Q] is a open standard protocol that is supported on switches from many vendors and most NICs.

What VTP mode allows you to change VLAN information on the switch?
Server mode

Which are the two trunking protocols ?
ISL and IEEE 802.1Q

Which Protocol encapsulate Etherframes ?
ISL encapsulate ethernet frames while 802.1Q tags ethernet frame

Which is the Vlan not tagged by 802.1Q ?
Native Vlan

How to delete vlan information from switch ?
VLAN information is not saved in the running-config or startup-config but in a separate file called vlan.dat on your flash memory. If you want to delete the VLAN information you should delete this file by typing delete flash:vlan.dat.

Difference between access and trunk mode ?
Access mode is used to connect end devices(hosts) to switches while trunk mode is used to connect between switches

Difference between dynamic auto and dynamic desirable ?
  • dynamic desirable : Attempts to negotiate a trunk with the other end
  • dynamic auto : Forms a trunk only if requested by the other end
what is the use of "nonegociate" command in switch ?
command disables automatic formation of trunk links.It will be good to configure trunk manually and give non-negociate command for security reason

Explain different switch port modes ?
  • Trunk : Forms an unconditional trunk
  • dynamic desirable : Attempts to negotiate a trunk with the far end
  • dynamic auto : Forms a trunk only if requested by the far end
  • access : Will never form a trunk 
what is DTP ?
Dynamic Trunking Protocol (DTP) is used to automatically establish trunks between capable ports (insecure method!)

Can we see trunk interfaces in show vlan command ?Nope

which is the command used to see trunk interfaces ?
  • show interface trunk
  • show interface Fa1/0/13 trunk 
  • show interface Fa1/0/13 switchport
  • show interfaces status | include trunk
what is the maximum number of vlans permitted in 802.1Q and ISL ?
  • Maximum Vlan permitted in 802.1Q is 4094
  • Maximum Vlan permitted in ISL is 1000
what is the header size of 802.1Q ?
4 bytes

what is the header size of ISL ?
26 bytes

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  1. in the 14th question the spelling of "nonegotiate" is wrong.. plz correct it

  2. Question 5
    the answer is desirable for the latest ios and auto for the old catOS