[c-nsp] 6PE FIB usage on 6500/7600

[Mark Tinka]

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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