PCQ Queues in MikroTik: Fair Bandwidth Distribution

Fair Bandwidth Sharing with PCQ (Per Connection Queue)

While Simple Queues give each IP address a fixed bandwidth limit, PCQ (Per Connection Queue) takes a different approach: it automatically divides available bandwidth equally among active users or connections. This is ideal when you want fairness without manually creating a queue for every user.

What is PCQ?

PCQ is a queuing discipline that splits bandwidth dynamically. Instead of assigning a fixed limit per user, PCQ observes all active flows and tries to give each one an equal share. If you have 10 users active, each gets roughly 1/10 of the total bandwidth.

PCQ is particularly useful for:

• Shared internet connections serving many users.
• ISP-style fair access policies.
• Preventing one heavy user from saturating the link while others are idle.

PCQ Concepts

• pcq-rate: Optional maximum rate per sub-stream (each classified flow). Set to 0 for no per-stream limit.
• pcq-limit: Queue depth per sub-stream (how many packets to buffer before dropping).
• pcq-classifier: What field is used to classify flows into sub-streams. Options: src-address, dst-address, src-port, dst-port.
• pcq-total-limit: Maximum total packets in the queue across all sub-streams.

Step 1: Create PCQ Queue Types

First, define the PCQ queue types for download and upload:

/queue type add name=pcq-download kind=pcq pcq-classifier=dst-address pcq-rate=0 pcq-limit=50 pcq-total-limit=2000
/queue type add name=pcq-upload kind=pcq pcq-classifier=src-address pcq-rate=0 pcq-limit=50 pcq-total-limit=2000

For download: classify by dst-address — each destination IP (your LAN users) gets a fair share.

For upload: classify by src-address — each source IP (your LAN users) gets a fair share.

Step 2: Create a Queue Tree

PCQ works best in a Queue Tree, which lets you set a total bandwidth limit and then apply PCQ within that total.

First, mark all traffic from the WAN interface (for download) and to the WAN (for upload):

/ip firewall mangle add chain=forward in-interface=pppoe-out1 action=mark-packet new-packet-mark=wan-download passthrough=yes
/ip firewall mangle add chain=forward out-interface=pppoe-out1 action=mark-packet new-packet-mark=wan-upload passthrough=yes

Then create the Queue Tree:

/queue tree add name=total-download parent=global packet-mark=wan-download max-limit=100M queue=pcq-download
/queue tree add name=total-upload parent=global packet-mark=wan-upload max-limit=20M queue=pcq-upload

Set max-limit to your actual ISP connection speed (100M down / 20M up in this example).

How PCQ Distributes Bandwidth

With the above setup and 100 Mbps total download:

• 1 active user → gets 100 Mbps
• 2 active users → each gets ~50 Mbps
• 10 active users → each gets ~10 Mbps
• 20 active users → each gets ~5 Mbps

PCQ dynamically adjusts as users start and stop downloading.

Setting a Per-User Maximum with pcq-rate

If you want each user to have a maximum (even when others are idle):

/queue type set pcq-download pcq-rate=10M
/queue type set pcq-upload pcq-rate=5M

Now no single user can exceed 10 Mbps download or 5 Mbps upload, regardless of what others are doing.

Viewing Queue Statistics

/queue tree print stats

Combining Simple Queue with PCQ

You can combine both approaches:

1. Use a Simple Queue to limit each user to a maximum (e.g., 20 Mbps).
2. Use PCQ inside that limit to distribute fairly when multiple users are active.

This requires Queue Trees with PCQ as the queue type on child queues.

PCQ vs Simple Queue: When to Use Which

Troubleshooting PCQ

• All users get low speeds: Check that max-limit on the Queue Tree matches your actual ISP speed.
• Classifier not working: Make sure you use dst-address for download and src-address for upload.
• Mangle marks not matching: Check that mangle rules are in forward chain and referencing the correct WAN interface.

Summary

• PCQ dynamically divides bandwidth fairly among active users.
• Create PCQ queue types with /queue type add kind=pcq.
• Use Queue Trees to apply PCQ to a total bandwidth limit.
• Use mangle marks to identify upload and download traffic.
• Set pcq-rate to cap per-user speed.
• PCQ is ideal for shared connections and ISP-style fairness.