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Tagged vs Untagged -HP3500

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  • 1.  Tagged vs Untagged -HP3500

    Posted Mar 17, 2022 01:54 PM

    On my tech support case 5362671567, I had a discussion on the automatic detection of VLAN, and the configuration thereof.
    In my current environment, I have a working twin 3500, with uplink to core on OSPF and the downlink to the edge on a "trunk"
    the "auto" VLAN detect works fine.
    here is the VLAN config:
    Area 12 main switch
    vlan 4
    name "VLAN 4 DATA"
    tagged 21-24
    ip address 10.12.4.1 255.255.252.0
    ip helper-address 10.1.100.100
    ip helper-address 10.1.100.11
    ip helper-address 10.1.100.10
    ip ospf 10.12.4.1 area 0.0.0.12
    ip pim-dense
    ip-addr any
    exit
    exit

    "Edge switch" trunked/tagged on port 24

    vlan 4
    name "VLAN 4 DATA"
    tagged 21-24
    no ip address
    exit

    ------------------------------------------------------------------

    The above setup works fine, on any PORT, I can plug in a phone, or a PC, gets DHCP all is happy.

    on the new setup exactly same config/doesn't work, unless I specify untagged i.e. no DHCP

    vlan 4
    name "VLAN 4 DATA"
    untagged 1-20
    tagged 21-24
    no ip address
    exit

    this presents several issues:
    Wireless AP VLAN


    Phones


    the techs are telling me that this is the way to do it:


    "We need to mention the vlan as tagged or untagged, Autodetect will not happen for all the vlan's only a default vlan could pass through all the links, the rest of the vlans should be mentioned.

    Can someone chime in 


    Software versions are 

    same



    K.16.02.0022m



    thank you





    ------------------------------
    Nicos Christofi
    ------------------------------


  • 2.  RE: Tagged vs Untagged -HP3500

    MVP GURU
    Posted Mar 19, 2022 11:57 AM
    Hi Nicos, I don't understand what do you mean when you say "Autodetect VLAN". Generally speaking you should verify that the VLAN membership of a downlink port matches the VLAN membership of an uplink port.

    To check the downlink ports check both downlink port (on the Core switch) and uplink port (on the Edge switch) with this command: show vlan ports <port-list> [detail]

    Side note: those ports aren't "trunks" in HP jargon, they are just single physical (down-/up-)links to other switches...calling them "trunk" because they are carring more than one VLAN (many tagged VLANs) is a typical Cisco approach, in HP jargon the "trunk" means "links aggregation" or "Port Trunking" which is a configuration your switches don't have, at least looking at what you posted).

    ------------------------------
    Davide Poletto
    ------------------------------



  • 3.  RE: Tagged vs Untagged -HP3500

    Posted Mar 21, 2022 01:00 PM
    David Poletto.  I see your point, however, the main question remains: Is there a default setting that doesn't show up explicitly in the configuration.   For example in some cases we connect   switch port  ---phone---desktop
    in this case the phone acts as a hub/switch running two VLANS, one trunked for phone, the second for the desktop as untagged?
    If on the same switchport I only attach a desktop I don't get a DHCP address.

    ------------------------------
    Nicos Christofi
    ------------------------------



  • 4.  RE: Tagged vs Untagged -HP3500

    MVP GURU
    Posted Mar 21, 2022 06:03 PM
    Hello Nicos,

    "Is there a default setting that doesn't show up explicitly in the configuration"

    Is it a question?

    If your above statement is particularly related to VLANs membership of switch ports then their default state, for the particular Switch series you are referring to (HP ProCurve, isn'it?), is the one where Port VLAN ID (PVID) is set to VLAN 1 and all ports are untagged members of that VLAN (their PVID or Native VLAN is 1).

    For your second issue, generally an unaware (or VLAN unconfigured = without VLAN Tag configured thus default) edge device should be connected to a port where you set (decide/impose) the VLAN tagging - for the accepted traffic ingressing the Switch port - the traffic will be tagged internally the Switch (that's the PVID or Untagged VLAN). When you have a VoIP terminal directly connectef (with/without a Workstation connected to) usually this requires the Voice dedicated VLAN (configured of type "voice" on HP ProCurve) to be configured as the Tagged VLAN ID on the Switch port while the Untagged VLAN ID should be the one designated for Data traffic (not necessarily VLAN 1, this per best practices). That way the VoIP terminal will work on Tagged VLAN and Wokstation should work on Untagged VLAN (PVID), provided that VoIP will be able to pass back that VLAN to connected Wokrstation.


    ------------------------------
    Davide Poletto
    ------------------------------