On Thursday, January 02, 2014 03:50:46 PM Tarko Tikan wrote: > What about QOS? MPLS EXP is a great way to carry QOS > markings without overriding TOS/DSCP/TC sent, seen and > used by customers.
So we support only DSCP and EXP. We don't generally perform QoS on IPP. For IP traffic, we trust DSCP values that come from Managed Service customers, i.e., we can vouch for the customer's QoS configuration on their end. We "can" trust DSCP values from customers that "know what they're doing", but deciding this is not always scientific. At any rate, customer- and core-facing ports are reasonably over-engineered such that if trusted customers were naughty enough to place unimportant traffic in important queues over an unscientifically trusted port, they'd only be hurting themselves and not other customers. For non-IP traffic (Ethernet, really), we don't care what TC IP markings customer packets come with. We only mark with EXP for core handling. So whatever TC values they send across are preserved (this wasn't always the case when "mls qos" was enabled on older Cisco switches, for example). For untrusted customer ports, we apply our own DSCP values. We also apply explicit EXP values to avoid the automated copying of the first 3 bits of the DSCP value to the EXP field (most annoying, but understandable). Mark.
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