When creating a VLAN, what does the priority setting actually do?



  • Can anyone explain how the priority setting when creating a VLAN in pfSense affects traffic? Would it function any different than if I setup a PRIQ traffic shaping rule on a VLAN interface after I created it?
    pfsense_vlan_priority.png


  • Galactic Empire

    802.1p values.

    https://en.wikipedia.org/wiki/IEEE_P802.1p

    If I set vlan 5 to proirity 5 I see the following:-

    Screenshot 2020-09-24 at 20.45.48.png



  • So from what I'm reading its QoS applied at the Layer 2 level. Maybe this is a dumb question but does that mean this is only really useful if I'm saturating my switch capacity?



  • @jhavlat

    More saturating the output to a single port. There's a problem with switches often called "funneling" where a port is overwhelmed with traffic from multiple ports. Beyond that, these days, it takes some effort to saturate a switch. If you're worried about end to end priority, you have to look at diffserv at the IP level.



  • @JKnott

    I could see that being a possibility on a trunk port but its never been a problem that I have witnessed. I don't personally have any traffic flow problems but I read a guide about setting up VLANs in pfSense for VoIP and they said it was absolutely critical to set the priority when creating the VLAN. I was just curious whether it provided much benefit or not.



  • @jhavlat

    Well, you have to understand the traffic on the LAN to say it's critical. With Gb LANs, it's not likely to be an issue, unless you have a lot of traffic. A lot of this sort of thing was developed back in the 10 Mb days, when it was easier to saturate a LAN.


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