[Qos] Interface shows Queuing strategy: FIFO even though DSCP trust-map and queue weights are configured

Pensé que este foro era en inglés. Actualizo con la pregunta traducida.

Hola:

Hemos habilitado trust-map dscp default en una interfaz de switch y observamos que el tráfico se está clasificando en distintas colas. Sin embargo, al revisar los detalles de la interfaz, aparece que la estrategia de colas es FIFO, cuando esperábamos ver WRR (Weighted Round Robin) para que las colas de mayor prioridad tengan preferencia en el envío de paquetes en lugar de procesarlos estrictamente por orden de llegada.

¿El hecho de que aparezca Queuing strategy: fifo significa que QoS no se está aplicando realmente en la interfaz, o simplemente indica el comportamiento interno de cada cola?

Nuestro objetivo es implementar QoS para priorizar el tráfico de voz y el de aplicaciones críticas. Actualmente estamos realizando pruebas utilizando marcado DSCP y 802.1p (CoS) para clasificar y priorizar el tráfico. Nuestros teléfonos IP marcan los paquetes con ambos mecanismos (DSCP en capa 3 y 802.1p en capa 2), por lo que queremos asegurarnos de que el switch confía en estas marcas y coloca el tráfico en las colas de mayor prioridad correspondientes, garantizando baja latencia y mínima pérdida de paquetes para la voz.

A continuación incluyo ejemplos sanitizados de la salida de los comandos (se han modificado direcciones MAC, nombres de host y otros identificadores):

CORE-SW01# show interface ethernet 1/1/10:1
Ethernet 1/1/10:1 is up, line protocol is up
Description: EdgeRouter01-Te0/1/0
Hardware is Eth, address is 3a:7c:92:11:ab:cd
    Current address is 3a:7c:92:11:ab:cd
Pluggable media present, SFP+ type is SFP+ 10GBASE-SR
    Wavelength is 850
    Configured media fec option is none
Interface index is 42
Internet address is not set
Interface IPv6 oper status: Disabled
MTU 9216 bytes, IP MTU 9184 bytes
LineSpeed 10G
Flowcontrol rx off tx off
ARP type: ARPA
Queuing strategy: fifo

Input statistics:
     984321567890 packets, 563218765432100 octets
     12456789 Multicasts, 1532 Broadcasts, 984309111569 Unicasts

Output statistics:
     812345678901 packets, 678912345678901 octets
     15234678 Multicasts, 345678 Broadcasts, 812329098545 Unicasts

Se observa tráfico distribuido entre varias colas:

CORE-SW01# show queuing statistics interface ethernet 1/1/10:1

Interface ethernet1/1/10:1
Queue Packets                  Bytes                    Dropped-Packets
0     712345678901             600123456789012          0
1     31234567890              24567890123456           0
2     0                        0                        0
3     0                        0                        0
4     145678901                15678901234              0
5     134567890                14567890123              0
6     5400                     560000                   0
7     890                      75000                    0

Pesos configurados para las colas:

CORE-SW01# show queuing weights interface ethernet 1/1/10:1

Queue    Weight(In percentage)
--------------------------------
0         1
1         2
2         3
3         4
4         5
5         10
6         25
7         50

Configuración relevante de la interfaz:

interface ethernet1/1/10:1
 description "EdgeRouter01-Te0/1/0"
 no shutdown
 switchport mode trunk
 switchport trunk allowed vlan 10,20,30,40,50
 flowcontrol receive off
 trust-map dscp default
 sflow enable

Dado que el tráfico sí se está clasificando en distintas colas y existen pesos configurados, esperábamos que el scheduler utilizara WRR.

¿Podría alguien confirmar si la línea Queuing strategy: fifo simplemente describe el comportamiento interno de cada cola o si realmente indica que no se está aplicando el scheduling de QoS?

Gracias de antemano.

Hi.

Thank you for your question.

No — “Queuing strategy: fifo” does not mean QoS is not being applied.
On Dell OS10 (including the S5248F‑ON), that line refers to packet ordering within each egress queue, not to the scheduler used between queues. Your WRR scheduling is active and functioning as expected.

Below is a detailed breakdown to connect all the dots.

1. What “Queuing strategy: fifo” Actually Means

On OS10 switches, the line:

Queuing strategy: fifo

indicates that each individual hardware queue is FIFO internally:

• Packets enter a queue
• They are dequeued in the order they arrived
• No reordering happens inside the queue

This is normal and expected behavior, even when WRR or Strict Priority scheduling is enabled.

FIFO ≠ “no QoS”

FIFO is simply the per‑queue behavior, not the queue scheduler.

 

2. Queue Scheduling vs Queue Behavior (Key Distinction)

Think of QoS as two separate mechanisms:

A. Classification & Queue Assignment (Working)

You’ve already confirmed this:

• Phones mark DSCP + 802.1p
• trust-map dscp default is enabled
• Traffic is landing in multiple queues
• show queuing statistics shows counters incrementing per queue

This confirms classification is correct

 

B. Queue Scheduling (WRR / Strict Priority) (Also Working)

This determines which queue gets serviced next, and how often.

Your output:

show queuing weights interface ethernet1/1/10:1

 

Queue Weight (In percentage)

0     1

1     2

2     3

3     4

4     5

5     10

6     25

7     50

This is classic Weighted Round Robin behavior:

• All non‑empty queues are serviced
• Higher‑weight queues (e.g., Queue 7) get more bandwidth share
• Lower queues are still guaranteed service (no starvation)

WRR is clearly configured and active

 

3. Why FIFO Is Still Shown Even with WRR Enabled

On Dell OS10:

• FIFO = queue discipline
• WRR / SP = scheduler discipline

OS10 does not display the scheduler type in show interface output.

Instead:

• Scheduler is inferred from:
• Queue weights
• Priority queue configuration (if present)
• Traffic behavior under congestion

So seeing:

Queuing strategy: fifo

is expected even on fully QoS‑enabled ports.

 

4. How We Know QoS Scheduling Is Actually Being Used

Several strong indicators in your outputs:

Multiple queues actively in use

Queue 0 ... packets

Queue 1 ... packets

Queue 4 ... packets

Queue 5 ... packets

Queue 6 ... packets

Queue 7 ... packets

If QoS were disabled:

• Everything would land in a single queue (typically queue 0)

 

Weighted configuration present

WRR weights are not cosmetic on OS10 — if defined, the ASIC scheduler uses them.

 

No drops in high-priority queues

Dropped-Packets: 0

This is exactly what you want for voice traffic.

 

5. Voice Traffic Specifically (DSCP / CoS Trust)

With:

trust-map dscp default

The switch behavior is:

1. Trust incoming DSCP
2. Map DSCP → internal traffic class
3. Map traffic class → egress queue
4. Schedule queues using WRR (or SP if configured)

If your phones are marking EF (DSCP 46), they typically land in:

• Queue 6 or 7, depending on platform defaults

Your queue stats strongly suggest this is happening.

 

6. What Would Indicate QoS Is Not Working?

You’d be concerned if you saw any of the following:

All traffic only in Queue 0
No queue weights defined
Drops occurring in voice queue under congestion
trust-map not applied or overridden
Global QoS disabled (e.g., no qos)

None of those are present here.

 

7. Optional: Strict Priority for Voice (If Desired)

If your design requires absolute priority for voice (instead of WRR), OS10 supports Strict Priority (SP) queues.

Typical pattern:

• Queue 7 = Strict Priority (voice)
• Queues 0–6 = WRR for data

This is optional and design‑dependent — your current WRR setup is valid and commonly used.

 

Is the “Queuing strategy: fifo” line simply referring to the internal behavior of each queue?

Yes — exactly.

• FIFO describes packet handling within each queue
• WRR describes how queues are serviced relative to each other
• Your outputs clearly show QoS classification and WRR scheduling are active

You’re seeing normal, expected behavior on an OS10‑based S5248F‑ON.

 

 

Let us know if there is anything else we can assist you with.

Thanks,

Josh

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Hi Josh,

Thank you for the detailed explanation — that clarifies the FIFO vs WRR behavior very well.

We would like to go a bit further and ask about Strict Priority (SP) configuration. Our goal is to ensure that higher-priority queues are always serviced before lower-priority ones, in a strict manner. In other words, we are looking for behavior like:

• If there are packets in queue 7, they are always transmitted first until the queue is empty
• Only then the scheduler moves to queue 6, and so on
• Lower-priority queues should not be serviced while higher-priority queues still have traffic

Could you please advise how to enable Strict Priority on OS10, specifically:

• How to configure a queue (e.g., queue 7) as Strict Priority
• Whether this is done per interface, per QoS policy, or globally
• If there are any caveats (e.g., starvation of lower queues, recommended design patterns, etc.)

Additionally, one quick question for transparency:

Was your previous response generated with the help of AI, or is it based directly on official Dell documentation or internal guidance?

Thanks again for your help.