====== Difference between ingress/egress qdisc ======


| Feature | Ingress Qdisc | egress Qdisc |
| Direction | Incoming traffic | Outgoing traffic |
| Common Usage | Policing (rate limiting) | Shaping, scheduling |
| Handle | ffff: | Custom (e.g., 1:) |
| Parent Keyword | parent ffff: | parent <handle>: |
| Shaping Support | ❌ Not supported | ✅ Supported |
| Example Qdisc | ingress | htb, fq_codel, tbf, etc. |
| create qdisc | tc qdisc add dev <interface> **handle ffff:** ingress | tc qdisc add dev <interface> **root handle** 1: htb default 10 |
| create filter | tc filter add dev <interface> **parent ffff:** \ \\ protocol ip prio 1 u32 match ip src 0.0.0.0/0 \ \\  police rate 1mbit burst 10k drop flowid :1 | tc class add dev <interface> **parent 1:** classid 1:10 htb rate 1mbit \\ tc filter add dev <interface> protocol ip **parent 1:** prio 1 u32 \ \\ match ip dst 0.0.0.0/0 flowid 1:10 |

Note: 
  * **handle ffff:** is a reserved handle for ingress and **parent ffff:** refers to the ingress qdisc.
  * **root** refers to the egress qdisc.
  * **police** is used to enforce rate limits.
  * **htb** is a **hierarchical** token bucket used for shaping.
  * **flowid** assigns traffic to **a specific class**.
  * **tc class** is only for egress qdisc, not ingress qdisc
  * **lowid :1** in this ingress command is a label or tag used for accounting and statistics: tc filter add dev <interface> parent ffff: protocol ip prio 1 u32 match ip src 0.0.0.0/0 police rate 1mbit burst 10k drop **flowid :1**



====== Example to create below queue structures ======

<code>
Queue 1 ─┐
Queue 2 ─┘→ Scheduler 1 → Scheduler 2 → Root Egress Qdisc (eth1)

Queue 3 ─┐
Queue 4 ─┘→ Scheduler 3 → Scheduler 4 → Root Egress Qdisc (eth1)
</code>

Note: 
  * use **tc class** to create queue/scheduler structure
  * use **tc filter** to map traffic to queue

<code bash t.sh>
# Step 1: Add root HTB qdisc to eth1
tc qdisc add dev eth1 root handle 1: htb default 100

# Step 2: Create top-level classes (Scheduler 2 and Scheduler 4)
tc class add dev eth1 parent 1: classid 1:10 htb rate 10mbit  # Scheduler 2
tc class add dev eth1 parent 1: classid 1:20 htb rate 10mbit  # Scheduler 4

# Step 3: Create second-level classes (Scheduler 1 and Scheduler 3)
tc class add dev eth1 parent 1:10 classid 1:11 htb rate 5mbit  # Scheduler 1
tc class add dev eth1 parent 1:20 classid 1:21 htb rate 5mbit  # Scheduler 3

# Step 4: Create leaf classes (Queues)
tc class add dev eth1 parent 1:11 classid 1:111 htb rate 2mbit  # Queue 1
tc class add dev eth1 parent 1:11 classid 1:112 htb rate 3mbit  # Queue 2

tc class add dev eth1 parent 1:21 classid 1:211 htb rate 2mbit  # Queue 3
tc class add dev eth1 parent 1:21 classid 1:212 htb rate 3mbit  # Queue 4

# Step 5: Attach filters to classify traffic into queues
# You can change IPs or match conditions as needed

# Queue 1: traffic from 192.168.1.1
tc filter add dev eth1 protocol ip parent 1: prio 1 u32 \
    match ip src 192.168.1.1/32 flowid 1:111

# Queue 2: traffic from 192.168.1.2
tc filter add dev eth1 protocol ip parent 1: prio 1 u32 \
    match ip src 192.168.1.2/32 flowid 1:112

# Queue 3: traffic from 192.168.1.3
tc filter add dev eth1 protocol ip parent 1: prio 1 u32 \
    match ip src 192.168.1.3/32 flowid 1:211
# Queue 4: traffic from 192.168.1.4
tc filter add dev eth1 protocol ip parent 1: prio 1 u32 \
    match ip src 192.168.1.4/32 flowid 1:212
</code>

Delete filter example:
  * filter del dev eth1 protocol ip parent 1: prio 1

Delete class example: 
  * tc class del dev eth1 classid 1:111  # Queue 1
  * tc class del dev eth1 classid 1:112  # Queue 2
  * tc class del dev eth1 classid 1:211  # Queue 3
  * tc class del dev eth1 classid 1:212  # Queue 4
  * tc class del dev eth1 classid 1:11   # Scheduler 1
  * tc class del dev eth1 classid 1:21   # Scheduler 3
  * tc class del dev eth1 classid 1:10   # Scheduler 2
  * tc class del dev eth1 classid 1:20   # Scheduler 4

Delete qdisc example:
  * tc qdisc del dev eth1 root

====== example to create multiple chains in the ingress qdisc ======


====== example to create multiple chains in the egress qdisc ======