Added quality of service(QOS) via Differentiated services (#330)
* Added quality of service(QOS) via Differentiated services * Altered to classify network traffic in Ingress * Updated readme for QoS
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exercises/qos/README.md
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exercises/qos/README.md
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# Implementing QOS
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## Introduction
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The objective of this tutorial is to extend basic L3 forwarding with
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an implementation of Quality of Service (QOS) using Differentiated Services.
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Diffserv is simple and scalable. It classifies and manages network traffic and provides QOS on modern IP networks.
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As before, we have already defined the control plane rules for
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routing, so you only need to implement the data plane logic of your P4
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program.
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> **Spoiler alert:** There is a reference solution in the `solution`
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> sub-directory. Feel free to compare your implementation to the reference.
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## Step 1: Run the (incomplete) starter code
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The directory with this README also contains a skeleton P4 program,
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`qos.p4`, which initially implements L3 forwarding. Your job (in the
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next step) will be to extend it to properly set the `diffserv` bits.
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Before that, let's compile the incomplete `qos.p4` and bring up a
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network in Mininet to test its behavior.
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1. In your shell, run:
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```bash
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make
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```
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This will:
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* compile `qos.p4`, and
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* start a Mininet instance with three switches (`s1`, `s2`, `s3`) configured
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in a triangle. There are 5 hosts. `h1` and `h11` are connected to `s1`.
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`h2` and `h22` are connected to `s2` and `h3` is connected to `s3`.
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* The hosts are assigned IPs of `10.0.1.1`, `10.0.2.2`, etc
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(`10.0.<Switchid>.<hostID>`).
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* The control plane programs the P4 tables in each switch based on
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`sx-runtime.json`
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2. We want to send traffic from `h1` to `h2`. If we
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capture packets at `h2`, we should see the right diffserv value.
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3. You should now see a Mininet command prompt. Open two terminals
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for `h1` and `h2`, respectively:
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```bash
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mininet> xterm h1 h2
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```
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4. In `h2`'s XTerm, start the server that captures packets:
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```bash
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./receive.py
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```
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5. In `h1`'s XTerm, send one packet per second to `h2` using send.py
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say for 30 seconds.
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To send UDP:
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```bash
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./send.py --p=UDP --des=10.0.2.2 --m="P4 is cool" --dur=30
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```
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To send TCP:
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```bash
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./send.py --p=TCP --des=10.0.2.2 --m="P4 is cool" --dur=30
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```
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The message "P4 is cool" should be received in `h2`'s xterm,
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6. At `h2`, the `ipv4.tos` field (DiffServ+ECN) is always 1
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7. type `exit` to close each XTerm window
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Your job is to extend the code in `qos.p4` to implement the diffserv logic
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for setting the diffserv flag.
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## Step 2: Implement Diffserv
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The `qos.p4` file contains a skeleton P4 program with key pieces of
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logic replaced by `TODO` comments. These should guide your
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implementation---replace each `TODO` with logic implementing the
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missing piece.
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First we have to change the ipv4_t header by splitting the TOS field
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into DiffServ and ECN fields. Remember to update the checksum block
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accordingly. Then, in the egress control block we must compare the
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protocol in IP header with IP protocols. Based on the traffic classes
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and priority, the `diffserv` flag will be set.
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A complete `qos.p4` will contain the following components:
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1. Header type definitions for Ethernet (`ethernet_t`) and IPv4 (`ipv4_t`).
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2. Parsers for Ethernet, IPv4,
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3. An action to drop a packet, using `mark_to_drop()`.
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4. An action (called `ipv4_forward`), which will:
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1. Set the egress port for the next hop.
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2. Update the ethernet destination address with the address of
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the next hop.
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3. Update the ethernet source address with the address of the switch.
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4. Decrement the TTL.
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5. An ingress control block that checks the protocols and sets the ipv4.diffserv.
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6. A deparser that selects the order in which headers are inserted into the outgoing
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packet.
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7. A `package` instantiation supplied with the parser, control,
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checksum verification and recomputation and deparser.
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## Step 3: Run your solution
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Follow the instructions from Step 1. This time, when your message from
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`h1` is delivered to `h2`, you should see `tos` values change from 0x1
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to 0xb9 for UDP and 0xb1 for TCP. It depends upon the action you choose
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in Ingress processing.
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To easily track the `tos` values you may want to redirect the output
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of `h2` to a file by running the following for `h2`
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```bash
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./receive.py > h2.log
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```
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and just print the `tos` values `grep tos h2.log` in a separate window
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```
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tos = 0xb9
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tos = 0xb9
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tos = 0xb9
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tos = 0xb9
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tos = 0xb9
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tos = 0xb9
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tos = 0xb9
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tos = 0xb9
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tos = 0xb1
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tos = 0xb1
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tos = 0xb1
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tos = 0xb1
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tos = 0xb1
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tos = 0xb1
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tos = 0xb1
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tos = 0xb1
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```
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### Food for thought
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How can we let the user use other protocols?
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### Troubleshooting
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There are several ways that problems might manifest:
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1. `qos.p4` fails to compile. In this case, `make` will report the
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error emitted from the compiler and stop.
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2. `qos.p4` compiles but does not support the control plane rules in
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the `sX-runtime.json` files that `make` tries to install using
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a Python controller. In this case, `make` will log the controller output
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in the `logs` directory. Use these error messages to fix your `qos.p4`
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implementation.
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3. `qos.p4` compiles, and the control plane rules are installed, but
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the switch does not process packets in the desired way. The
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`/tmp/p4s.<switch-name>.log` files contain trace messages
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describing how each switch processes each packet. The output is
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detailed and can help pinpoint logic errors in your implementation.
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The `build/<switch-name>-<interface-name>.pcap` also contains the
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pcap of packets on each interface. Use `tcpdump -r <filename> -xxx`
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to print the hexdump of the packets.
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#### Cleaning up Mininet
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In the latter two cases above, `make` may leave a Mininet instance
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running in the background. Use the following command to clean up
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these instances:
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```bash
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make stop
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```
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