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QoS when interconnecting switches (2600-PWR)

Adrian O'Shea
Occasional Contributor

QoS when interconnecting switches (2600-PWR)

Dear Support,
I have IP phones that mark traffic (DSCP 40), I need to know what settings I should use for the following.

If switches are connected in a stack, does the stack port (1000BASE-T) need special config?

If remote switches are connected to the core stack do these require additional config? (i.e. do they need to be trunk ports)

Thanks in advance.

Regards, Adrian.
Sietze Reitsma
Respected Contributor

Re: QoS when interconnecting switches (2600-PWR)


i'm not from support

You can do diffserv marking. I assume that the voice traffic is handled in a separate voice vlan. In that case you can mark DSCP 40 with 802.1p priority (5 or 6).

If voice is carried via tagged links than the priority will be automatically honoured on layer 2.

use the command:
qos dscp-map .......

Adrian O'Shea
Occasional Contributor

Re: QoS when interconnecting switches (2600-PWR)

Many thanks for your assistance, unfortunately the phones have a built in dual port switch that have pc's attached too (they wanted to save the expenses of having the office re-cabled). So I am unable to separate the phones and pc's for this reason.
The phones already mark traffic with the DSCP value of 40, but just need to know how best to ensure that both stacked switches and satellite switches prioritise this traffic.
Thanks again. Regards, Adrian.
Bruce Campbell_3
Valued Contributor

Re: QoS when interconnecting switches (2600-PWR)

If you rely on the phone supplied DSCP setting, and have the phones and PCs
on the same vlan, an application on
the PC can arbitrarily choose a higher
priority. For this reason it is preferable
to separate voice and data into separate
vlans, and re-apply the DSCP based on
vlan. There are other reasons
to separate the phones from the PCs,
like preventing a misconfigured PC
from stealing the IP of a phone, etc.

But since you can't do that, you could
re-apply the DSCP based on udp or tcp
port, or IP address.

Or just hope nothing on the PC
messes with priorities, and rely
on the phone supplied setting.

Even though the voice and data are
arriving on the same vlan, configure
the switches so traffic leaves the
switch tagged. That way it will
maintain the 802.1p priority.
Bruce Campbell
Director, Network Services
Information Systems and Technology
MC 1018
(519)888-4567 x38323
University of Waterloo, Waterloo, ON