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Cisco vs. HP ProCurve VLAN switch ports

Posted in Networking.

Usually, when Cisco oriented networker sets off to the HP networking world, first confusing thing is VLAN port assignment. When speaking about VLAN ports in HP world, the ports can be tagged or untagged (despite the access / trunk ports in Cisco). As you may guess, tagging means 802.1q tagging in Ethernet frames.

It is important to realize that Cisco is “port-centric”, whereas Procurve is is “vlan-centric” when speaking about vlan port assignment.

Cisco

int f0/1
 switchport mode access
 switchport access vlan 2

HP

vlan 2
 untagged 1

In Cisco you configure the port and set which VLANs pass through (trunking mode) or to which VLAN the configured port belongs (access mode).
In Procurve you configure the VLAN and tag the ports (as cisco’s trunking mode – all frames are tagged with VLAN ID) or untag the ports (as cisco’s access mode – all frames are stripped of any VLAN ID)

no untagged

This is probably the most confusing part in HP switch world. Besides the tagged and untagged port, the port can be also ‘no untagged’. The ‘no untagged PORT_ID’  in VLAN 1 means that the port has been moved untagged into a different VLAN. At factory defaults, all ports start out untagged in the default VLAN 1.

Example:

  1. All ports are by default in VLAN1, like:
    vlan 1
    untagged a1-a24
  2. Then, VLAN2 is created and port a10 is added to VLAN2:
    vlan 2
    untagged a10
  3. VLAN1 state a10 as no untagged (port is no more member of vlan2) – it looks like it is redundant information and should occur just in VLAN1:
    vlan 1
    untagged a1-a9,a11-a24
    no untagged a10
    vlan 2
    untagged a10

Summary

access port = untagged port
trunk port = tagged port (802.1Q)

Possible modes:

  • Tagged – When a port is tagged, it allows communication among the different VLANs to which it is assigned.
  • Untagged – When a port is untagged, it can only be a member on one VLAN.
  • No untagged – The port is not a member of that VLAN.
  • Forbid – The port is “forbidden” to join that VLAN.