l2 to l3/bridging the gap...

  a vlan is a layer 2 construct, a pointer to layer 3, an association by layer 2 to layer 3...
vlan=network=subnet=broadcast domain

  a broadcast domain is the set of devices which may receive broadcasts... a layer 3 device is the defining element of the broadcast domain... a switch creates more and smaller collision domains with each additional port it places within the domain... a layer 3 device creates an additional broadcast domain with each port it introduces...  a switch floods broadcasts, multi-casts and unknown unicasts to every device in the domain... a layer 3 device recieves all broadcasts from a connected switch, and drops them (unless otherwise defined)... a layer 3 device defines the broadcast domain with that action...this layer 3 device is affectionately known as a router... vlan=network=subnet=broadcast domain


  a vlan number is the only requirement when creating a vlan. of course it's fairly useless without ports added to it, and a descriptive name would be nice also, but these are not required...

  an end-to-end vlan spans the entire switched network and should be avoided as such, a local vlan remains local (within its group) and is preferred...

  a vlan trunk can carry multiple vlans' traffic across the network

 isl encapsulates a frame for tagged transit whereas the preferred method of tagging is 802.1q, which injects a 4 byte field into the frame... 802.1q does not tag the native vlan; the native vlan is identified by the lack of a tag...

  dtp is dynamic trunking protocol.  it is a trunking negotiation mechanism...

  the native vlan is a settable parameter and is vlan1 by default... it is recommended to change the native vlan to something other than 1 after bringing the switch up... it is important to match the native vlans between switches to avoid annoying cdp messages, and sometimes derailed traffic...