From: Fabrice Paz (fabrice.paz@googlemail.com)
Date: Sat Jan 13 2007 - 15:06:22 ART
Thanks for this Bob,
I knew that cs3 was 011000 but for some reason never associated with value
24 (DSCP 24).
It's all coming clear to me now, cs3 = 011000 = DSCP24
Regards,
Fabrice
On 13/01/07, Bob Sinclair <bob@bobsinclair.net> wrote:
>
> Fabrice,
>
> Consider the following. It sounds to me like you might be confusing CS3
> with CoS 3.
>
> CS3 is a name for DSCP value 24; both are simply binary value 011000 (16
> plus 8).
>
> The CoS-dscp map is used for incoming traffic; the dscp-CoS map is used
> for
> outgoing traffic.
>
> If the outgoing link is a trunk, then the CoS is written to the frame. If
> the outgoing link is access then CoS is just used for queueing.
>
> HTH,
>
> Bob Sinclair
> CCIE 10427 CCSI 30427
> www.netmasterclass.net
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Fabrice Paz
> Sent: Friday, January 12, 2007 7:42 AM
> To: ccielab@groupstudy.com
> Subject: QoS; I don't understand Internal DSCP and "show mls qos interface
> statistic" command
>
> Hi all,
>
> Hope that someone will be able to help and not fall asleep before reaching
> the end of my email...
>
> I have some trouble understanding Internal DSCP and in order to understand
> I
> have done the following testing;
>
>
> I have plugged a laptop generating traffic to port GigabitEthernet1/0/35
> of
> a Catalyst 3750G (IOS 12.2(25)SEB4).
>
>
> interface GigabitEthernet1/0/35
> description Laptop connexion
> switchport access vlan 415
> switchport mode access
> service-policy input marking
> end
>
> and configured a simple policy to mark all the traffic coming from the
> laptop as cs3
>
>
> ip access-list extended Testing
> permit ip any any
>
> class-map match-all testing
> match access-group name Testing
>
> policy-map marking
> class testing
> set dscp cs3
>
>
> All the traffic is leaving the switch via trunk interface
> GigabitEthernet1/0/1
>
> interface GigabitEthernet1/0/1
> description Trunk
> switchport trunk encapsulation dot1q
> switchport mode trunk
> mls qos trust dscp
>
>
> Here the problem (or the bit that I don't understand), when I issue the
> command "show mls qos interface gigabitEthernet 1/0/1 statistics" in order
> to see if all the packets leaving the switch (only one laptop is plugged)
> are marked as cs3 (value 30) I have the following.
>
>
> dscp: outgoing
> -------------------------------
> 0 - 4 : 0 0 0 0 0
> 5 - 9 : 0 0 0 0 0
> 10 - 14 : 0 0 0 0 0
> 15 - 19 : 0 0 0 0 0
> 20 - 24 : 0 0 0 0 397
> 25 - 29 : 0 0 0 0 0
> 30 - 34 : 0 0 0 0 0
> 35 - 39 : 0 0 0 0 0
> 40 - 44 : 0 0 0 0 0
> 45 - 49 : 0 0 0 0 0
> 50 - 54 : 0 0 0 0 0
> 55 - 59 : 0 0 0 0 0
> 60 - 64 : 0 0 0 0
>
> cos: outgoing
> -------------------------------
> 0 - 4 : 0 0 0 397 0
> 5 - 7 : 0 0 0
>
>
> You can see that packet are marked with DSCP 24 and COS 3. Since my policy
> is marking the traffic effectively (otherwise it would be DSCP 0 and COS 0
> by default) the IOS should not use COS-DSCP default map to set the
> internal
> DSCP.
>
>
> TestSwitch#show mls qos map
>
> Dscp-cos map:
>
> d1 : d2 0 1 2 3 4 5 6 7 8 9
> ---------------------------------------
> 0 : 00 00 00 00 00 00 00 00 01 01
> 1 : 01 01 01 01 01 01 02 02 02 02
> 2 : 02 02 02 02 03 03 03 03 03 03
> 3 : 03 03 04 04 04 04 04 04 04 04
> 4 : 05 05 05 05 05 05 05 05 06 06
> 5 : 06 06 06 06 06 06 07 07 07 07
> 6 : 07 07 07 07
>
>
> Cos-dscp map:
>
> cos: 0 1 2 3 4 5 6 7
> --------------------------------
> dscp: 0 8 16 24 32 40 48 56
>
>
> As I was becoming crazy I decided to use a packet sniffer to later realize
> that all packets where marked correctly as cs3 (011 000)
>
> Why all the packets leaving the switch are showing as DSCP 24 when using
> show mls qos stat command?
>
> Is that command related to what Cisco call Internal DSCP which seems to be
> different that the real IPv4 DSCP?
>
> Do you know a way to see what really is the final IPv4 DSCP marked by the
> policy?
>
> Thanks
>
> Fabrice
>
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