Connecting 5400 and 1620

[mrobertson8180]

I have an established network of 5400 series switches.  They are all interconnected on a switch vlan via fiber.  Those ports are untagged vlan XXX.

I recently bought a new 1620.  I used the console cable to give it an IP on my "switch" vlan XXX.  One the switch i'm connected it to, i untagged the uplink port on that same vlan XXX.

I plugged in the 1620, and it works fine.

However - i don't understand why the 2 are connecting.  When i look at the web GUI of the 1620 it clearly shows untagged membership in the default vlan 1.

I'm just confused how the 2 are talking?!?!?

If i set the 1620 to untagged membership in vlan XXX, the 2 will stop communicating.

Thoughts?!?!?

P.S. This thread has been moved from Switches, Hubs, Modems (Legacy ITRC forum) to ProCurve / ProVision-Based. - Hp Forum Moderator

[Vince-Whirlwind]

You have 2 questions:

 - Why are the switches communicating when you haven't configured VLAN XXX on the 1620:

Because you are patched via untagged ports, the packets going between the 5400 and the 1620 are not in the dot1q format, ie, they contain no VLAN tags, therefore the two switches can think the switched frames belong to whatever VLAN they want.

We call this "bridging" - you have bridged VLAN1 on the 1620 with VLAN XXX on the 5400.

- If i set the 1620 to untagged membership in vlan XXX, the 2 will stop communicating.

If you want the 1620 to properly join VLANXXX, you would need to:
 - create VLANXXX on the 1620

 - Give the VLANXXX interface the correct IP address for the subnet that lives on VLANXXX

 - change the VLAN and PVID assignment on the uplink port to the 5400 from VLAN1 to VLANXXX

 - (perhaps, I don't know how the 1620 works, but cheap switches usually need this) change the "management VLAN" on the 1620 from VLAN1 (default) to VLANXXX