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QoS Configuration

Configure per-subscriber traffic shaping with CAKE qdisc.

Overview​

The qos section configures Quality of Service (QoS) via CAKE (Common Applications Kept Enhanced):

  • Per-subscriber rate limiting (download and upload)
  • Overhead profile adjustment for different encapsulations
  • Ingress shaping via a per-session Intermediate Functional Block (IFB) device
  • Integration with RADIUS for per-subscriber and dynamic rate changes

Downstream (to subscriber) shaping is an egress CAKE qdisc on the subscriber's access interface — the demux VLAN for DHCP/IPoE (e.g. sub0.1234.2) or the ppp interface for PPPoE (e.g. ppp0). Upstream (from subscriber) shaping is applied on a per-session IFB device named ifb<session_id> (e.g. ifb10).

Configuration Options​

enabled​

Enable or disable QoS (optional).

qos:
  enabled: true

Type: Boolean
Required: No
Default: false
Valid values: true, false

CLI:

abng# set qos enabled true

default_down​

Default download rate for subscribers (optional).

qos:
  default_down: "100mbit"

Type: String (bandwidth format)
Required: No
Default: None
Format: <number><unit> (e.g., "100mbit", "1gbit", "50kbit")

Valid units: kbit, mbit, gbit

CLI:

abng# set qos default_down "100mbit"

default_up​

Default upload rate for subscribers (optional).

qos:
  default_up: "40mbit"

Type: String (bandwidth format)
Required: No
Default: None
Format: <number><unit> (e.g., "40mbit", "1gbit", "10kbit")

Valid units: kbit, mbit, gbit

CLI:

abng# set qos default_up "40mbit"

default_overhead_profile​

Default overhead profile for CAKE (optional).

qos:
  default_overhead_profile: "pppoe_ethernet"

Type: String
Required: No
Default: "pppoe_ethernet"
Valid values: Key from overhead_profiles

Purpose: Adjusts CAKE overhead calculation for the encapsulation type.

CLI:

abng# set qos default_overhead_profile "pppoe_ethernet"

overhead_profiles​

Custom overhead profiles for different encapsulations (optional).

qos:
  overhead_profiles:
    pppoe_ethernet:
      overhead: 34
      mpu: 64
    ipoe_ethernet:
      overhead: 22
      mpu: 64

Profile Options​

overhead​

Overhead bytes for the encapsulation (required).

overhead_profiles:
  pppoe_ethernet:
    overhead: 34

Type: Integer
Required: Yes
Constraints: Non-negative integer

Calculation:

  • PPPoE: 8 bytes (PPPoE header) + 2 bytes (PPP header) + 20 bytes (IP header) + 4 bytes (FCS) = 34 bytes
  • IPoE: 14 bytes (Ethernet) + 4 bytes (FCS) + 4 bytes (VLAN) = 22 bytes
mpu​

Minimum Packet Unit (optional).

overhead_profiles:
  pppoe_ethernet:
    mpu: 64

Type: Integer
Required: No
Default: 64
Constraints: Non-negative integer

Purpose: Minimum size for rate calculation (prevents underestimation of small packets).

Example Configurations​

Minimal QoS Configuration​

qos:
  enabled: true
  default_down: "100mbit"
  default_up: "40mbit"

Uses default overhead profile (pppoe_ethernet).

Full QoS Configuration​

qos:
  enabled: true
  default_down: "100mbit"
  default_up: "40mbit"
  default_overhead_profile: "pppoe_ethernet"
  overhead_profiles:
    pppoe_ethernet:
      overhead: 34
      mpu: 64
    ipoe_ethernet:
      overhead: 22
      mpu: 64
    pppoe_qinq:
      overhead: 38
      mpu: 64

Different Rates by Service​

pppoe:
  enabled: true

dhcp:
  enabled: true

qos:
  enabled: true
  default_down: "100mbit"
  default_up: "40mbit"
  default_overhead_profile: "pppoe_ethernet"
  overhead_profiles:
    pppoe_ethernet:
      overhead: 34
      mpu: 64
    ipoe_ethernet:
      overhead: 22
      mpu: 64

Configuration via CLI​

Enable QoS​

abng> configure
abng# set qos enabled true
abng# commit

Set Default Rates​

abng# set qos default_down "100mbit"
abng# set qos default_up "40mbit"
abng# commit

Set Overhead Profile​

abng# set qos default_overhead_profile "pppoe_ethernet"
abng# commit

Add Custom Overhead Profile​

abng# set qos overhead_profiles custom_profile overhead 40
abng# set qos overhead_profiles custom_profile mpu 64
abng# commit

Verification​

View QoS Configuration​

abng> show configuration | match "^qos:"
qos:
  enabled: true
  default_down: 100mbit
  default_up: 40mbit
  default_overhead_profile: pppoe_ethernet
  overhead_profiles:
    pppoe_ethernet:
      overhead: 34
      mpu: 64

View Applied QoS Policy​

abng> show qos
┌────┬──────────────┬─────────────┬──────┬──────┬────────────────┬────┬───────┐
│ ID ┆ Username     ┆ Interface   ┆ Down ┆ Up   ┆ Profile        ┆ OH ┆ IFB   │
│ 1  ┆ -            ┆ sub0.1234.2 ┆ 250M ┆ 100M ┆ ipoe_ethernet  ┆ 22 ┆ ifb1  │
│ 10 ┆ testuser@isp ┆ ppp0        ┆ 250M ┆ 100M ┆ pppoe_ethernet ┆ 34 ┆ ifb10 │
└────┴──────────────┴─────────────┴──────┴──────┴────────────────┴────┴───────┘

View Live Throughput​

abng> show qos statistics
┌────┬──────────────┬─────────────┬────────┬──────┬─────────┬─────────────┬─────────┬─────────┐
│ ID ┆ Username     ┆ Interface   ┆ Dir    ┆ Rate ┆ Current ┆ Transferred ┆ Dropped ┆ Backlog │
│ 1  ┆ -            ┆ sub0.1234.2 ┆ ▼ down ┆ 250M ┆ 46Kbps  ┆ 3.1 MB      ┆ 0       ┆ 0       │
│    ┆              ┆             ┆ ▲ up   ┆ 100M ┆ 1Kbps   ┆ 2.1 KB      ┆ 0       ┆ 0       │
└────┴──────────────┴─────────────┴────────┴──────┴─────────┴─────────────┴─────────┴─────────┘

Current is a 5-second average sampled and cached by abng-qos from the CAKE qdiscs — live throughput for shaped sessions only. For cumulative per-session totals across all sessions (including unmetered ones), see the per-session accounting counters (Bytes In / Bytes Out) in show subscribers detail and over SNMP, described in Subscriber Sessions — Per-Session Accounting. See also the operational-mode CLI reference.

Check CAKE Qdisc​

tc qdisc show
qdisc cake 8001: dev ppp0 root refcnt 2 bandwidth 100Mbit diffserv4 ...
qdisc cake 8002: dev ifb10 root refcnt 2 bandwidth 100Mbit diffserv4 ...

Check abng-qos Logs​

sudo journalctl -u abng-qos -f

Integration with RADIUS​

QoS rates come from RADIUS per-subscriber via the Athena vendor-specific attributes (VSAs):

radius:
  servers:
    - host: "10.255.0.10"
      secret: "your-secret"

RADIUS attributes:

  • Athena-Rate-Down — Download rate (e.g., "250mbit")
  • Athena-Rate-Up — Upload rate (e.g., "100mbit")

Values are strings like "250mbit"/"100mbit"; the parser also accepts gbit, kbit, and plain bps. This applies to both DHCP/IPoE and PPPoE.

A subscriber with no rate attribute (no plan) is left unmetered — abng-qos skips shaping when the rate is 0 rather than applying a 0-bandwidth qdisc.

RADIUS response example:

Athena-Rate-Down = "250mbit"
Athena-Rate-Up = "100mbit"

Overhead Profile Reference​

PPPoE over Ethernet (Standard)​

pppoe_ethernet:
  overhead: 34
  mpu: 64

Breakdown:

  • Ethernet frame: 14 bytes (dst MAC 6 + src MAC 6 + type 2)
  • PPPoE header: 6 bytes (version/type 1 + code 1 + session ID 2 + length 2)
  • PPP header: 2 bytes (protocol 2)
  • IP header: 20 bytes (minimum)
  • FCS: 4 bytes (frame check sequence)
  • Total: 46 bytes (rounded to 34 for typical usage)

IPoE over Ethernet​

ipoe_ethernet:
  overhead: 22
  mpu: 64

Breakdown:

  • Ethernet frame: 14 bytes
  • VLAN tag: 4 bytes
  • FCS: 4 bytes
  • Total: 22 bytes

PPPoE over QinQ​

pppoe_qinq:
  overhead: 38
  mpu: 64

Breakdown:

  • Ethernet: 14 bytes
  • Outer VLAN: 4 bytes
  • Inner VLAN: 4 bytes
  • PPPoE: 6 bytes
  • PPP: 2 bytes
  • IP: 20 bytes
  • FCS: 4 bytes
  • Total: 54 bytes (rounded to 38)

Validation Rules​

FieldValidation
enabledBoolean
default_downValid bandwidth format (e.g., "100mbit")
default_upValid bandwidth format (e.g., "40mbit")
default_overhead_profileMust exist in overhead_profiles
overhead_profiles[].overheadNon-negative integer
overhead_profiles[].mpuNon-negative integer

Best Practices​

  1. Default Rates — Set reasonable defaults for your subscriber base
  2. Overhead Profile — Match your actual encapsulation (PPPoE vs IPoE)
  3. RADIUS Override — Use RADIUS for per-subscriber rate customization
  4. Monitoring — Monitor CAKE qdisc stats for congestion
  5. Testing — Test with iperf to verify rates
  6. Ingress Shaping — Enable IFB for ingress (upload) shaping
  7. Documentation — Document your overhead calculations

Troubleshooting​

QoS Not Applying​

  1. Check QoS is enabled: show configuration | match qos
  2. Check CAKE qdisc exists: tc qdisc show
  3. Check abng-qos logs: journalctl -u abng-qos -f
  4. Check session is active: show subscribers

Rates Not Matching Expected​

  1. Check overhead profile: show configuration | match overhead_profiles
  2. Verify with iperf: iperf -c <subscriber-ip> -t 10
  3. Check CAKE stats: tc -s qdisc show dev ppp0
  4. Adjust overhead if needed

IFB Ingress Shaping Not Working​

  1. Check IFB device exists: ip link show | grep ifb (per-session ifb<id>)
  2. Check ingress qdisc: tc qdisc show dev ifb<session_id>
  3. Check abng-qos logs: journalctl -u abng-qos -f

Next Steps​