[c-nsp] Define MPLS default EXP value?

[Tony]

There have been a couple of good answers already, but if you really want to change what EXP value is assigned to packets that have no other TOS marking, then you could also look at changing the dscp-exp map.

>From what I have read (and I'm happy to be corrected on this) the PFC based QoS defines an "internal DSCP" value from the TOS/COS bits on a packet and then uses this to determine most QoS actions.

There is a map that determines which DSCP value is mapped to which EXP value. You can see it with the command "show mls qos maps dscp-exp". If you wanted your default traffic to be something other than EXP-0, you could change the map so that DSCP-0 maps to something else, like this:

mls qos map dscp-exp 0 to 5

Which would remap DSCP-0 to EXP-5 in this example so that any packets that were DSCP-0 would become EXP-5.

I do think the suggestion on just leaving everything as EXP0 (for "normal" traffic) is the best. This is what we do and specifically remark anything that is "less than best effort" to EXP-1. It will probably be much simpler in the long run.


regards,
Tony.

--- On Sat, 31/7/10, Patrick Abeldt <abeldt at cip.ifi.lmu.de> wrote:

> From: Patrick Abeldt <abeldt at cip.ifi.lmu.de>
> Subject: [c-nsp] Define MPLS default EXP value?
> To: cisco-nsp at puck.nether.net
> Received: Saturday, 31 July, 2010, 12:57 AM
> Hi all,
> 
> we're planning to introduce MPLS within our network
> backbone, among other
> things for QoS purposes. Our current concept is based
> solely on using EXP
> values for different priority levels (the IP TOS fields
> need to be left
> unchanged.)
> 
> Aside from applications which require higher-than-normal
> forwarding
> priorities, we have a small number of traffic flows which
> we'd like to
> assign a lower-than-normal priority. As far as I can see,
> this would
> require an EXP value > 0 for standard traffic. More
> precisely, I'd need to
> set a specific default EXP value for all labels imposed on
> a MPLS router,
> regardless of interface etc. Are there easy methods to
> achieve this goal,
> preferably on the global configuration level?
> 
> The only solution I've found so far is to impose that
> default EXP value
> via a service policy attached to the respective interfaces.
> But given the
> number of interface configs, this would be extremely
> cumbersome to manage,
> and additionally it would interfere with existing service
> policies. I
> think this is definitely not the way to go.
> 
> Any suggestions regarding an alternative design would be
> also welcome.
> We're using c6500/Sup720/PFC3 devices with IOS version
> s72033-advipservicesk9_wan-mz.122-33.SXI3.
> 
> Thanks for your advice,
> Patrick
> 
>