HPE 1820-24G Vlan setup

[ITEsonic]

Hello,

I apologize, but i am desperate.

It's possible to have two VLAN on one port on switch HPE 1820-24G? (for example Vlan101, 102)

I tried multiple time setup with tagged and untagged, but without any successful job. 

Example:

Port: 1 (Vlan 101, 102) Tagged to both

Port: 2 (Vlan 102) Untagged to 102

When i connect to port 1 (vlan 101, 102) on switch, which should be able to see port 2 with vlan 102,  but i can´t see. Do you know, where can be a problem, or it´s not possible to do this.

Thank you very much for your answer.

[Emil_G · Accepted solution]

Hello

When a port is a tagged member of 2 VLANs and doesnt have untagged membership in any VLAN, it will only accept Ethernet frames containing a VLAN tag with the VLAN ID of the supported VLANs. Frames without a VLAN tag will be discarded. The same applies to outgoing traffic: packets originating from VLAN 101 will have a VLAN tag with ID 101 resp 102 with VLAN ID 102.

That means it is important to know what type of device are you connecting to port 1? Is this device capable of sending frames with a VLAN tag and specifying the VLAN ID?

Most of the end devices like PCs or laptops dont support VLAN tags by default (IP phones usually do support VLAN tags). While most of them will accept frames with VLAN tag, ignore the VLAN information and process them,  the problem is that they also send out frames without VLAN tag which are dropped by the switch. 

VLAN tags are supported mainly by switches and other network infrastructure devices, also by some servers, IP phones typically include an integrated switch and also support VLANs. For this reason ports which are tagged members of multiple VLANs are typically used to interconnect switches not connect end devices to switches. End devices are typically not aware of VLANs and are connected to untagged ports in the respective VLAN. A port can have only one untagged VLAN membership which is fine for end devices because they need to send traffic mostly in a single VLAN.

What would be the purpose of making port 1 tagged in two VLANs in your case? What type of device should be connected?

If you are testing with a normal PC, then for a short test just make VLAN 102 untagged on port 1 while VLAN 101 remains tagged. The PC should be able to communicate with the device on port 2. But of course it wont be able to communicate in VLAN 101.

If your PC and NIC support VLAN tagging then you should configure it to support VLAN 102 and this should also work with your currenct VLAN config.

[ITEsonic]

Hello Emil,

First thank you for your answer I appreciate that. What you wrote was really helpful and it helped me clarify my problem.

"What would be the purpose of making port 1 tagged in two VLANs in your case? What type of device should be connected?"

I just wanted to test communicate between devices (ping) and i was startled, that doesn't work, that i cant see device on other vlan, when i am connected to port which is in two vlans.

When you wrote, that i must have a network card which must support vlan tagging. I started search on google and i found, that can be setup on my laptop at network adapter in properties - VLAN ID. Where can i specify, which vlan i want to select. But it possible only on supported network card of course.

So my problem was solved, thank you and have a nice day.

[Emil_G]

Hello @ITEsonic 

Thanks for your feedback!
Just to add some additional clarification if I undestand you correctly. End devices like PCs (with a single wired NIC) are only connected to single VLAN (which typically corresponds with a single IP subnet) and for this reason the port should be untagged in this VLAN. If you want the PC to see devices in different VLANs (subnets) then it is not necessary to make the PC port member of this other VLANs. Communication between VLANs is handled by the routing switch or router which is configured as default gateway on your PC (or provided with the DHCP lease). This is called inter VLAN routing. So all you need is your PC to have configured or obtain via DHCP the correct IP of the default gateway. The port of a PC should remain in a single VLAN. Even if you enable VLAN tagging on the NIC it can still communicate only in a single VLAN not in 2 VLANs at the same time. PCs or servers with more than 1 wired NIC can be in more than 1 VLANS at the same time but they also connect to more than 1 port.

HPE 1820 is a layer 2 switch and it cannot work as default gateway so it will forward the packets destined to another VLAN via its uplink to the default gateway. The default gateway will place the traffic in the other VLAN and send it back to the 1820.

The main use case for having multiple tagged VLANs on a port is to interconnect switches. This helps to maintain VLAN separation when the switches support more than one VLAN and traffic for all this VLANs has to be forwarded via a single interface.