QOS question posted 09/08/2008
- Subject: QOS question
- From: Geert Nijs <Geert.Nijs@xxxxxxxx>
- Date: Mon, 8 Sep 2008 11:36:14 +0200
- Accept-language: en-US, nl-BE
- Acceptlanguage: en-US, nl-BE
- Content-language: en-GB
- Thread-index: AQHJEZZWLC9ECBsgyE2+2/EflfJGQA==
- Thread-topic: QOS question
I have some particular QOS questions, especially regarding ingress and outgress interfaces.
cos is a field present in dot1q links only.
If an access port is configured with:
switchport mode access
switchport access vlan 103
switchport voice vlan 203
mls qos trust cos
what happens if:
- the port receives a frame without cos header, but with DSCP set to AF41 ??
- is this considered cos 0 ? internal qos marking: DSCP 0 ?
implied: no cos header, so default cos 0
- is this considered cos 4 ? internal qos marking: DSCP CS4 ?
implied: switch used dscp_to_cos map to derive cos from dscp
and then used cos_to_dscp to get the internally used DSCP value.
- is this considered dscp41 ? internal qos marking: DSCP AF41 ?
implied: if no cos field is present, switch takes dscp field as is.
If this packet is transmitted on the uplink and dscp rewrite is enabled (default setting), this packet
will have a DSCP of 0 in the first case (loosing DSCP marking), DSCP CS4 (loosing drop probability) in the second case and DSCP AF41 in the third case (i presume no other policy-maps are present that recolor packets).
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