QoS best-effort in C1300

[krzysztofmaciejewskiit]

I need to configure the switches so that every movement, without exception, is treated as best-effort. I have no implementation experience in QoS, so I have prepared this configuration and am wondering if it will be sufficient.

switch(config)#qos basic
switch(config-if)#no qos ?
  cos Configure the default CoS value for a port. Use the no
  form of the command to return to the default setting.
  statistics QoS statistics counters
  trust Configure each port to trust state while the system is
  in basic mode. Use the no form of the command to
  disable trust state on each port.

switch(config-if)#no qos cos
or
switch(config-if)#qos cos 0
switch(config-if)#no qos trust

switch#show running-config interface GigabitEthernet1
  interface GigabitEthernet1
  no qos trust
  switchport access vlan 333

Will this configuration normalize traffic to best-effort? Frames from this switch then go to the next aggregating switch, so I would like them to be normalized as close to the source as possible so that they do not need to be normalized on the aggregating switch.

[Joseph W. Doherty]

I would need to dig into C1300 documentation, for your IOS version (which is?) to specifically answer your question for specific configuration commands.  I would also need to know the specifics for the traffic flows, through the C1300, to which you want to apply.  Lastly, need clarification on whether L2 CoS (if VLAN tagged frames) and/ot L3 QoS tags need to be set to BE (which I believe you desire) or just your C1300 only provides BE treatment regardless of frame/packet tag.

Also, as you mention switches (plural) are all C1300s and/or edge devices?

BTW, in older switches, by default, QoS was disabled and no remarking.  If QoS enabled, all traffic (again by default) marked BE and treated as such (the latter often increasing drop rates).

Newer switches now appear, by default, have a very basic active QoS policy.  If everything is to be treated BE, you may want to reallocate QoS resources.

[krzysztofmaciejewskiit]

C1300 version is 4.1.3.36.
The C1300 will be connected to a C9k, an access connection, for the purposes of a single VLAN.
I found the following in the documentation:


I also find that default value is CoS = 0.


I found something similar in the global QoS settings, but it cannot be disabled, and I am not sure if it makes any difference in my case.


This sends a command to the interface, which, as I understand it, will set CoS = 0, and that is what interests me (I hope). Because from what I have read, DSCP is in L3 traffic.

This gives us the following settings:


If I understand correctly, I assume that no further action is required on other devices, as the access switch normalizes the frames? If I am mistaken, please let me know, as I have no experience in this area.

[KJK99]

Hi Krzysztof,

Here's my take on this and I hope I properly read your message.

"best-effort" is probably not the best term here. I have never seen it in the networking switch context, but I do know it from working on much higher-level messaging systems. It was about the best-effort vs guaranteed message delivery. Switches do not offer guaranteed delivery so it's always best-effort.

As for "normalization," switches do it by their nature and nothing special needs to be done. QoS is about prioritization of certain traffic and will not do any kind of "normalization."

[krzysztofmaciejewskiit]

Let me outline what I want to achieve more precisely, and you can try to help me. The task is “simple.” Every traffic flow must be treated identically, even if an endpoint sends a frame with a higher “priority,” it should be treated the same as all other frames without that priority.
There should be no situation where traffic from one host is given higher priority over other traffic.

[Joseph W. Doherty]

From your OP ". . .  I would like them to be normalized as close to the source as possible so that they do not need to be normalized on the aggregating switch."

So, besides the C1300 treating all traffic alike (both directions?), you want any packet with a non-BE marking to be remarked to BE?

[Joseph W. Doherty]

Although "normalization" is probably far from an ideal term, "best-effort" is very much used in QoS discussion (L2 or L3), and as most smart switches, and L3 switches, support QoS, using CoS and/or QoS tags, it's, I believe, an ideal term for what OP is trying to achieve, especially as further described in a follow-up reply by OP.

BTW, generally, no transit network device really guarantees delivery, although end-to-end protocols like TCP can often confirm receipt.  Also, QoS encompasses more than just prioritization of some traffic.

[krzysztofmaciejewskiit]

It doesn't have to be called best-effort, that's just what I called it—I'm not familiar with the subject, so I'm asking specialists for help.

My goal is for every packet in both directions to be treated the same by the switch. I don't know what it's called. Next, my traffic goes to the aggregation switch, and there I would like the CoS and DSCP tags to be reset (in fact, they should already be reset at the C1300 output).

Don't focus on what I called it - as I wrote, I have no experience with this. I think I described what I want to achieve well, but I can clarify something if necessary.

@Jens Albrecht As far as I know, disabling QoS does not reset its tags. This traffic will then go on to other network devices, so I would like it to go there with reset tags.

[Jens Albrecht]

Hello @krzysztofmaciejewskiit,

if you want to revert the switch to classic best-effort forwarding for all packets, this can be achieved with just a few steps:

• Login to the Web UI.
• Switch to Advanced Mode (change the view in the top right to "Advanced" if not already done).
• Navigate to: Quality of Service > General > QoS Properties
• Set QoS Mode to "Disable" (this turns off QoS on the switch and forwards all traffic as best-effort).
• Click “Apply” to save the change to running configuration.

That's all. 

No further configuration is needed per-port as QoS is now globally disabled on the switch.

HTH!

[Joseph W. Doherty]

Ah, well that saves me some research, as the C1300 appears to allow QoS to be disabled.

However, @Jens Albrecht , besides frames/packets not receiving any QoS treatment, does that also force switch to reset CoS and/or QoS to BE?  (Possible the latter is also desired for subsequent switch processing.  See my last reply to OP.)

[krzysztofmaciejewskiit]

Supported by artificial intelligence (with caution), or as I wrote in my first message, setting the port to untrust mode will not reset all tags?


switch#show running-config interface GigabitEthernet1
  interface GigabitEthernet1
  no qos trust
  switchport access vlan 333

Also check this https://community.cisco.com/t5/routing/what-happens-to-marked-packets-without-qos-trust-on-port/td-p/1659373 

[Jens Albrecht]

Well, in case of the classic IOS switches the answer is clear and simple.
If QoS is disabled, they reset any values to the default DSCP 0.
I've seen this happen many times when a network team forgot to activate QoS just on a single switch at any branch location.

So my expectation is that the Catalyst 1300 switches should do the same BUT since they run this stripped down Linux flavor firmware you'd better use Wireshark to prove it.

[Joseph W. Doherty]

---

@Jens Albrecht wrote:

Well, in case of the classic IOS switches the answer is clear and simple.
If QoS is disabled, they reset any values to the default DSCP 0.
I've seen this happen many times when a network team forgot to activate QoS just on a single switch at any branch location.

So my expectation is that the Catalyst 1300 switches should do the same BUT since they run this stripped down Linux flavor firmware you'd better use Wireshark to prove it.

---

What I recall (???), in older (smaller) switches (like 2960/3560/3750 and earlier), if QoS was disabled, switch performed like a "dumb", i.e. no QoS treatment, frame/packet tagging not touched.  If QoS enabled (and trust not configured), there was an implied very basic QoS policy and all frames/packets tags reset to zero.  (The reset happened before egress processing, so, by default, all traffic would be treated based on a zero CoS/ToS tag.

The later generation switches, by default, had an active basic implied QoS policy (pretty similar to what the earlier generations switches did when QoS enabled, although they, also by default, trusted the CoS/ToS tag.

IMO, what software routers usually did, no QoS operations, including resetting CoS/ToS tag, unless so explicitly configured.

[krzysztofmaciejewskiit]

Thanks for that information.
Was the CoS counter also reset to zero? Because from what I've read, both counters should be reset (DCSP and CoS)?
Do you use any good programmes that generate frames for such purposes?

[Joseph W. Doherty · Accepted solution]

Okay, what should work for you, using Basic QoS mode, set trust mode to use DSCP, enable the Override Ingress DSCP, and then change all DSCP values to use zero.