# [XDP (eXpress Data Path) Playground](https://github.com/foxhoundsk/xlb/tree/xdp-playground)
A playground for newbie to the XDP.

[Slide](https://docs.google.com/presentation/d/1XIbH5RYABRJDPjxMzMRLe3MncDy7AOQz4AWKPBY7f44/edit?usp=sharing)

## Environment Setup
We use Clang as compiler for the eBPF, which requires at least `v3.4.0` in order to build eBPF program.

Note that [GCC also has support for eBPF since version 10](https://www.phoronix.com/scan.php?page=news_item&px=GCC-10-eBPF-Port-Lands).

First, create a virtual network environment for playing with the XDP safely:

$ sudo ./testenv.sh setup --name=play

Now, we have the following environment:

+-----------------------------+                          +-----------------------------+
| Root namespace              |                          | Testenv namespace 'play'    |
|                             |      From 'play'         |                             |
|                    +--------+ TX->                RX-> +--------+                    |
|                    | play +--------------------------+  veth0   |                    |
|                    +--------+ <-RX                <-TX +--------+                    |
|                             |       From 'veth0'       |                             |
+-----------------------------+                          +-----------------------------+

where the network namespace is in short a separated environment against the default network namespace, which contains your phy./virt. NIC. It allows you to do arrangement for the NICs or test network configurations safely and neatly.

Add an alias for convenient ops later:

$ alias t='sudo ip netns exec play'

## Packet Dropping
This lab hooks a XDP program which drops all of the incoming packets.

Assume you are under the root directory of the playground, run command:

$ make

to build the eBPF programs.

> If somehow your `make` command failed, it might be caused by lacking the following packages:
> - gcc-multilib
> - libelf-dev
>
> Simply install these packages solves the build error.

If all goes well, we have eBPF programs located at the root directory now.

`ping` the interface (`play` here) inside the root namespace to ensure that it works properly:

$ t ping fc00:dead:cafe:1::1

Run the following command to hook the eBPF packet dropping program onto the interface we just created:

$ sudo ip link set dev play xdp obj play.o sec drop

`ping` again, still replying?

$ t ping fc00:dead:cafe:1::1

If not, the eBPF program is now working, cheers!

Note, you can check whether the XDP program is loaded by run command:

$ ip a

There should exist an entry like this:

7: play@if6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp/id:128 qdisc noqueue state UP group default qlen 1000
    link/ether 96:44:47:1d:de:0f brd ff:ff:ff:ff:ff:ff link-netns play
    inet6 fc00:dead:cafe:1::1/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::9444:47ff:fe1d:de0f/64 scope link 
       valid_lft forever preferred_lft forever

where `xdp/id:128` indicates that the interface has XDP program loaded, and the program has ID `128`, which may varies on your machine.

## Packet Filtering
This lab hooks a XDP program which filters packet with odd sequence number within the ICMP header.

Run the following command to unload the previously loaded eBPF program:

$ sudo ip link set dev play xdp off

Hook the packet filtering program onto the interface:

$ sudo ip link set dev play xdp obj play.o sec filter

`ping` the interface, how is the reply going?

If you see only even seq. number `ping` replies, then we have managed to filter the odd ones with XDP.

## Tearing Down the Environment
Simply run:

$ sudo ./testenv.sh teardown; unalias t

You are now outside of the playground, see ya!

## XLB
Except `bpf/play.c`, `testenv.sh`, `config.sh` and `setup-env.sh`, the rest of the files are all XLB related sources. If one is interested in, `xlb_intro.md` contains its build instructions and usage. Enjoy your journey!