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QOS on the 100 series unmanaged switches
Thought I would answer the question here regarding QOS features within the 100 series switch family.
Lets see what I can give hopefully it's not too confusing. I grabbed the following from a internal discussion on QOS on 100 series switches.
Hey, we are talking about unmanaged switches, so QOS has to be hardwired with hopefully optimum with pre-defined settings.
Because these are Cisco Small Business switches, you will see references below to LVS phone RTP. As an example, the silicon within the switches will honor and queue according to priority settings on our SPA phones.
QoS Support with the 100 series unmanaged switches - some rules.
Unmanaged switches supports egress queuing based on DSCP and 802.1p , such that,
for up to 8 port switches, upon receiving Tagged frame with 802.1p bits and a DSCP, the switch will choose use the 802.1p value to assign the packet to one of two egress queues..
for 16 oports and above, upon receiving a tagged frame with 802.1p bits and DSCP the switch will use DSCP to assign to one of four egress queue. This is the reverse behaviour when compared to 8 port switches.
For untagged packets, any DSCP value is used to to assign the packet to a egress queue.
The switches within this family also incorporate Priority queue with weighted-round-robin (WRR).
So in summary;
Up to and including eight port switches
Umanaged up to 8 ports, will look at 802.1p bits and ignore DSCP values if both are present. With untagged packets, the switch prioritizes based on DSCP values.
Sixteen port switcehs and above
On sixteen port and above switches, will look at DSCP values and ignore 802.1p CoS values, if both are present.. With untagged packets, the switch prioritizes based on DSCP values.
Following chart shows DSCP to egress queue mapping for switches with, or more than 16 ports..
Now lets look at the smaller unmanaged switches.
SF100D-08 supports in silicon, 7 predefined DSCP values set to High priority queue: DSCP values 46 (EF), 10 (AF11), 18 (AF21), 26 (AF31), 34 (AF41), 48 (CS6), and 56 (CS7).
Ok what does this mean, these 8-port unmanaged switches recognizes only 7 predefined DSCP values and 802.1p, but has only two egress queues per port. If it sees these matching DSCP value and no 802.1p bits, it will queue these packets into a higher priority queue, else all traffic will use a lower priority egress queue. If it sees a tagged packet with these matching DSCP values but also a 802.1p but, it will ignore the DSCP values.
Which every way you look at it, there is a way to differentialte and actually utilize some QOS or COS in a unmanged switch. cool stuff
As said further up in this posting, SF100D-08/P supports 2 egress queues whose WRR weight assignment 1:16 (6%-94%), as seen from the normal or High settings in the table above.
Queues shown as 1,2,3,4 in the table above, reference the default WRR behaviour for sixteen port switches and above.
This switch is a transparent bridge to IPv4 and IPv6 packets.
The switches support DSCP values from IPv6 packets, except SF100D-08/P
(SF100D-08/P switches ignore the value of the DSCP on the IPv6 packets and take untagged-IPv6 as default priority traffic).