This post gives a comparison between the different port modes available on the Dell PowerConnect switches. the trunk and access modes are familiar to anyone who understands tagged and untagged transmission, the general mode however allows a lot more flexibility with port configurations.
- Trunk: all packets transmitted are tagged. Untagged received traffic is dropped. Tagged received traffic is dropped if it is not tagged in one of the member vlans. with later firmware versions, i have observed the switches to allow reception of untagged traffic, but not transmission. Thus, courtesy this behavior, the trunk port can now have an effective native vlan.
- Access: all packets are transmitted untagged. Untagged received traffic is accepted and switched in the ports define vlan. Tagged received traffic is dropped.
- General: can be configured to transmit tagged or untagged traffic per vlan. Untagged received traffic is accepted and switched in the defined PVID. Tagged received traffic is dropped if it is not in one of the port’s tagged vlans.
switchport mode access
switchport access vlan 99
Is equivalent to this:
switchport mode general
switchport general allowed vlan add 99 untagged
switchport general pvid 99
switchport mode trunk
switchport trunk allowed vlan add 99,100
Is equivalent to:
switchport mode general
switchport general allowed vlan add 99,110 tagged
switchport general pvid 4095 (this is the drop vlan)
brother can you please elaborate pvid concept hete.. is it reference towards PRIVATE Vlans ?
You can think of pvid as a declaration of “Native” or “Untagged” VLAN on the port. General mode is only a variation of trunk ports.
On Powerconnect switches, trunk port only allows transmission of tagged frames, but no untagged frames (It would however, allow reception of untagged frames at ingress, which are switched in the default vlan on the port). General mode, though, allows both tagged and untagged frames for both ingress and egress.
When you compare this to Cisco, trunk mode on Cisco can allow both tagged and untagged frames to be configured on a port. therefore, you can say the powerconnect mode general is actually what a trunk mode on Cisco is.
A Cisco trunk port is assigned a default port VLAN ID (PVID) for a VLAN on which all untagged traffic will travel. Any untagged or tagged traffic with a NULL (unassigned) VLAN ID, is assumed to belong to the VLAN with the port default PVID. The equivalent Cisco command for declaring pvid on a trunk link (.1Q) would be “switchport trunk native VLAN xx”
Porting this to Powerconnect, the above is true for the behavior of a “general” port. the pvid is declared through the command “Switchport general pvid xx”. one command i find particularly helpful in determining port behavior for VLAN tagging is “show interface switchport gigabit/tengig xx”, which breaksdown the membership and tagging behavior nicely for you on the Powerconnect switches.
hope this helps, but if not, please do flag and i shall be happy to advise further.
Dude THANK YOU. I come from CISCO, i had no idea why I couldn’t get my management VLAN through on these dells.
Your article helped me resolve a big issue with the wireless access in my new workplace; the switches had not been configured correctly for multiple VLANs. Thank you very much!