MQC & where DSCP or 802.1p remarking take effect

Created: Oct 3, 2019 15:34:17Latest reply: Oct 4, 2019 02:46:40 89 1 0 0
  Rewarded Hi-coins: 0 (problem resolved)

Hi all. This is a bit lengthy, but hopefully I've explained it clearly.

I came across the following paragrah in post QoS Issues - Issue 2 QoS Implementation - MQC and it has left me a bit confused:

remarking

I set up the following simple experiment using an S5720:

  • Port g0/0/1 configured as an access port on VLAN2542 connected to PC1 running wireshark

  • Port g0/0/2 configured as a trunk port with port trunk allow-pass vlan 2542 (so VLAN 2 packets egress this port tagged) connected to a PC2 which is also running wireshark & can see 802.1Q VLAN tags

  • The following classifier/behavior/traffic-policy defined & applied to port g0/0/1:

    traffic classifier EF operator or

     if-match dscp ef

    traffic behavior EF

     statistic enable

     remark 8021p 4

    traffic policy EF

     classifier EF behavior EF

    interface GigabitEthernet0/0/1

      traffic-policy EF inbound

  • I then [successfully] pinged PC1 --> PC2 to take care of ARP & MAC tables on the switch

  • reset qos queue statistics all on the switch

  • Next I used PC1 to inject 50 handcrafted packets destined for PC2 with DSCP value EF destined for PC2. These were actually ping requests and PC2 duly replied with ping responses.

  • With Wireshark on PC2 I observed that the ingressing crafted ping requests contained DSCP value EF & 802.1p CoS value 4. This is what I expected to see.

  • But when I examined the g0/0/2 queues using display qos queue statistics interface g0/0/2 I observed that my 50 packets egressed via queue 4. This is great, but not what I expected. Based on the highlighted paragraph above I was expecting to see these packets scheduled to egress queue 0 (noting that there is no trust configured on g0/0/1).


Have I misunderstood the paragraph, or is this an error?


Thanks in advance.




  • x
  • convention:

Featured Answers
chenhui
Admin Created Oct 4, 2019 02:46:40 Helpful(1) Helpful(1)

hi,
The paragraph you highlighted indicates the pripority remarking doesn't affects the processing queue on the local device, doesn't mean unchanging the priority.
For example, when remarke the queue from 0 to 4, it will be considered as queue 0 on the local device, but when transmitting out, it will be remarked to 4
  • x
  • convention:

All Answers
chenhui
chenhui Admin Created Oct 4, 2019 02:46:40 Helpful(1) Helpful(1)

hi,
The paragraph you highlighted indicates the pripority remarking doesn't affects the processing queue on the local device, doesn't mean unchanging the priority.
For example, when remarke the queue from 0 to 4, it will be considered as queue 0 on the local device, but when transmitting out, it will be remarked to 4
  • x
  • convention:

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