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A5500 VLAN Tagged and Untagged Ports

 
AtticaNet
Advisor

A5500 VLAN Tagged and Untagged Ports

If a A5500 switch hosts several VLANs (100 to 130) and the access ports (used by PCs) can only be untagged, how does the switch know to which VLAN a packet belongs to?

6 REPLIES
Justin_Goldberg
Valued Contributor

Re: A5500 VLAN Tagged and Untagged Ports

It will be programmed as such.

It will say:

interface GigabitEthernet 1/0/1
vlan 100 untagged
vlan 101 tagged
etc....
paulgear
Esteemed Contributor

Re: A5500 VLAN Tagged and Untagged Ports

To clarify further: each port can have only 1 untagged VLAN, so all untagged packets from PCs will always be in the untagged VLAN for that port.

The above syntax is incorrect for all Comware versions i've used. You would instead use something like this:

vlan 100
description Nice long description
name short-name
vlan 101
description Another nice long description
name short-name-2

interface GigabitEthernet1/0/1
port link-mode bridge
description port description goes here
port link-type trunk
port trunk permit vlan 100 101
port trunk pvid vlan 100
Regards,
Paul
AtticaNet
Advisor

Re: A5500 VLAN Tagged and Untagged Ports

Let me describe the following scenario

  • Two computers connected to one switch (A550-A) need to communicate to two other computers connected to another switch (A5500-B)
  • The computers A and C are connected to ports assigned to the VLAN 100 and their port is access type. Therefore the VLAN 100 is untagged.
  • The computers B and D are connected to ports assgined to the VLAN 101 and thier port is also access type. Hence untagged.
  • The two switches are connected through fiber on port 25 on each end. Therefore this port is configured as trunk and permits VLAN 100 and 101 to pass through. On both switches the PVID is VLAN 100.

How will B and D communicate is the trunk port can only have 1 untagged VLAN? Do I need a separate fiber connection for another trunk port dedicated for VLAN 101?

 

Regards.

paulgear
Esteemed Contributor

Re: A5500 VLAN Tagged and Untagged Ports

You have set up the switches exactly right for the different systems to communicate on their respective VLANs, as long as the PVID and tagging are set correctly on both ends of the switch-to-switch link.

 

You can verify the correct setup of the VLANs from the CLI by running 'display vlan 100' and 'display vlan 101' - this will tell you which ports are tagged and untagged.  As long as this confirms what your intended setup is, it should be working.

 

If it's not working, there is likely some other issue, like local firewalls on the workstations.

Regards,
Paul
AtticaNet
Advisor

Re: A5500 VLAN Tagged and Untagged Ports

Right. But if the trunk port (which is only 1 for each switch) can only have 1 VLAN untagged (VLAN 100) the tagged  VLAN 101 will not be able to communicate anything between PCs (B and D) since these are connected to an access port which has an untagged VLAN 101, right?. Therefore I believe I needed anothed trunk port just for VLAN 101 also untagged.

paulgear
Esteemed Contributor

Re: A5500 VLAN Tagged and Untagged Ports

No, the switch will automatically work out the tagged vs. untagged and send the right data across the right ports. All tagged & untagged ports in VLAN 101 are still in the same VLAN.

Tagged VLANs were designed with exactly this purpose in mind. You can add as many VLANs as required to the same inter-switch link by tagging them.
Regards,
Paul