If a VLAN isn't designated on an interface on a 3550 does it default to VLAN1? I was just checking a 3550 that was programmed a while ago and it has no VLAN assignment on interface 1. Is this normal? There are a total of three VLAN's on this switch.
Vlan 1 is the default vlan that a port will be in if you don't allocate it to a different vlan or you don't make the port a trunk. If theport has been made a trunk the native vlan will still be vlan 1 unless you change it.
It is best practice to create a non-routed vlan to place unused ports in rather than leave them in vlan 1. We use vlan 998 for this at work.