Cisco switch connecting to HP switch (vlan/interface question)

[chiseledst]

Can someone help me understand basic interface switching between a cisco and HP switch? Anyone familiar with HP lingo?

So I needed to connect a new Aruba with a Cisco switch today. On the cisco, the interface I used, I set as a trunk port with native vlan 10, and 10,15,20 allowed on the trunk.

Now, on the Aruba, the uplink port I was using was simply set to vlan 10 untagged, vlan 15,20 tagged. I also set a static IP and the management vlan to 10. This was an instanton Aruba switch which means it was a web gui switch so I don't know what the CLI commands would be to set management vlan to 10. Everything worked. I was able to connect to the static IP and the Aruba was online.

I then took the Aruba and needed to plug into another location as a new replacement (i was setting it up in my office first). I get to the location, I use the existing uplink cable to the uplink port I was using on the Aruba and the switch does not come online. I then go back to my office where the cisco switch is and change the uplink port on the Aruba to TAGGED vlan 10 which got it working at the location.

The location where it was getting the vlan traffic from another switch was not set up like the cisco in my office. If a cisco port is set to native vlan 10, even though i have 10 allowed on the trunk, are these frames being "untagged" in HP lingo? My suspicion is that the uplink cable at the location did not have vlan 10 as native vlan like I did in my office. Which is why the vlan 10 frames needed to be "tagged" at the location. Is this correct? Sorry it's hard to explain all this in a summarized manner, and plus I'm pretty beginner with cisco let alone HP....

[Richard Burts · Accepted solution]

You ask "If a cisco port is set to native vlan 10, even though i have 10 allowed on the trunk, are these frames being "untagged" in HP lingo?" and the answer is yes in Cisco the native vlan sends frames that are untagged.

[Richard Burts]

I am glad that my explanation was helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

[chiseledst]

I have one more question about HP/Cisco crossover. If vlan 15 and vlan 20 are allowed on the trunk of the uplink from the cisco, this would mean these frames are going to the Aruba as “tagged” correct? But on the Aruba, the ports where I needed to use either vlan 15 or 20, I set to untagged 15/20 for the device to work. How come? If the frames are tagged, wouldn’t these ports on the Aruba that will be using 15 or 20 need to be tagged?

[Richard Burts]

A switch port can be configured as either a trunk port or an access port (Cisco terminology, perhaps Aruba uses different terminology but would have the same concept about how they work). A trunk port can carry frames from multiple vlans. To identify which vlan the frame being forwarded belongs to the sending switch attaches a tag to the frame. The receiving switch looks at the tag and identifies which vlan to forward to. On the trunk port one vlan is forwarded without a tag. Cisco calls this the native vlan. I am not sure what terminology Aruba uses for this but the concept is used by all switch manufacturers. An access port belongs to a single vlan. So there is no need for a tag on an access port.

If Aruba receives a tagged frame it examines the tag and determines which vlan to forward to (15 or 20) and uses the access port in that vlan to forward the frame which has no tag at that point.