From: Petr Lapukhov (petrsoft@gmail.com)
Date: Mon Mar 20 2006 - 05:25:42 GMT-3
Hello David,
This is an interesting question, which puzzles me too :)
Here are some of my thoughts.
What we have:
1) DSCP/IPP marks IP traffic
2) CoS marks non-IP and IP-traffic
When you have IP packet arriving for classification from trunk port,
you could see it marked with both DSCP and CoS.
Now, if we trust DSCP, or set DSCP, the output CoS gets modified according
to DSCP->CoS map.
if we just set CoS or trust CoS, internal DSCP is deducted from CoS->DSCP
map, output DSCP is set accordingly to mapping (for IP traffic).
We could also:
1) Trust CoS and let DSCP pass thru.
2) Trust DSCP and let CoS pass thu.
I think, the value that is _trusted_, actually defines policing and
scheduling
process.
--Now, the last option. We can trust DSCP, and we can set CoS manually at the same time, in policy map.
How will scheduling/policing work in that case?
I guess switch will use DSCP value (which is trusted) for policing, and DSCP->CoS map should guide scheduling process. CoS value will _not_ get modified according to DSCP->CoS map
HTH Petr
2006/3/20, david robin <robindavi@gmail.com>: > > Hi all, > I have a question regarding mls qos in catalyst the doc cd said that the > command : > > mls qos cos policy-map > (Optional) Define the CoS value of a port in a policy map. > When you enter this command, you must also enter the trust > dscp policy-map configuration command in Step 8 and the set > cos new-cos policy-map configuration command in Step 9. > > I dont know, shall we trust the dscp and set the cos together in order to > work ?, Also if we set > the cos value what is the function of the dscp-to-cos map here ? > > best regards, > > _______________________________________________________________________ > Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html
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