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Forum Discussion
Netgear switch VLAN PCP support
Hi there, I'm wondering if theGS108 Netgear switch has hardware support for the PCP in the VLAN tag? My guess is no, but I want to hear from the experts here.
Below is my experiments:
Setup:
I enabled advanced 802.1Q VLAN configuration for my GS108Ev3 switch. In the netgear switch GUI in the browser, I added VLAN 100 group with all the ports in the member list, and all the ports are in "Tag All" mode for VID 100. The PVID list is in the default state (all ports PVID is set to 1).
I created VLAN interfaces on my two linux mahines, and configured vlan qos on Linux to set PCP 5 to streams egress at the vlan interfece. So streams going through the VLAN interfaces shall have PCP value 5.
Then I start testing using iperf.
Results:
I stream iperf UDP traffic from one Linux machine to the other, via the Netgear switch. There's one normal UDP stream and one VLAN tagged UDP stream, both transmitted using the one same ethernet cable. In wireshark I see the packets going through the VLAN interfaces have 802.1Q tag and the priority value is 5. Correct.
Problem:
I don't see any prioritized effect in the iperf stream performance. Both normal stream and VLAN tagged stream equally share the bandwidth. To be specific, I have one 100Mb link between the two linux machines, and I stream one normal 120 Mbps UDP stream and one VID 100 UDP stream, also at 120Mbps. The streams saturated the link. I would expect the VLAN tagged stream to take up more bandwidth and have less packet loss rate due to its high priority value (5 instead of 0 by default). But it is not the case. Therefore I guess the Netgear switch does not really prioritize the stream based on the PCP value inside the VLAN tag at the hardware level. Am I right about this?
Thanks in advance!
10 Replies
The switch core has just a smaller amount of queues as common in this switch world, something like four forwarding Queues in fact, something like High, Medium, Normal, and Low.
In 802.1q and DSCP, settings, we have no control in the Web UI about the 802.1q priority -> Queue resp. DSCP Class Selector (CS)/Assured Forwarding (AF)/Expedited Forwarding (EF) -> Queue mapping.
In my opinion, the documentation and ideally the on-line help should hold a reference to the implied queue mappings. This is something missing all over the documentation of the simple Web Managed (earlier designate Smart Managed Plus).
In your test case, I would assume a 802.1p PCP of 5 should make a difference from the default 1 (or 0) however.
Regards,
-Kurt
PS. I'll requesta moderator to move this thread to the Business -> Smart Plus And Smart Pro Managed Switches Forum section (even if the same question could apply to the GS808E/GS810EMX models here).Thanks for the reply. A small update.
I found out if I don't set any port speed limit on the Netgear switch, then the PCP prioritization works for the VLAN tagged stream. However, as soon as I limit the egress port on Netgear from the default 1Gbps to 100Mbps (which I need for my experiments), then the prioritization effect is gone. The two UDP streams start sharing the bandwidth equally again.
In short, the port speed limit config overwrites the previous queue mapping config, although the PCP value is still set to 5.
It would be really helpful if the issue can be resolved.
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