DNS Filter

NVIDIA DOCA DNS Filter Reference Application

This document provides an example of DNS filter implementation on top of NVIDIA® BlueField®-2 DPU.

1. Introduction

Domain name system (DNS) translates domain names to IP addresses so browsers can load internet resources. Each device connected to the internet has a unique IP address which other machines use to find the device.

The DNS process includes several steps:

Once a user tries to log into a website using a browser, the user's device creates a DNS query and sends it to a DNS resolver.
The DNS resolver queries the DNS domain to get an IP address by searching its cache or sending the request to another DNS server.
Once a match is found, the DNS resolver returns the correct IP matching the DNS domain.
The user can log into the required website using the correct IP.

DNS filter is used to offload DNS requests from the host to the BlueField DPU Arm which allows reducing CPU overhead as Arm allows further DNS processing to be done (e.g., whitelisting, logging, filtering, etc).

2. System Design

The DNS filter application is designed to run as a "bump-on-the-wire" on the BlueField-2 DPU instance. The DPU intercepts the traffic coming (ingress traffic) from the wire and either passes it to the Arm or forwards it to the egress port using hairpin. The decision is made by traffic classification.

3. Application Architecture

The DNS filter runs on top of DOCA FLOW to classify DNS requests.

Ingress packet types are identified using pipes which encapsulate flow rule matching patterns and actions.
Matched flows are identified, and FORWARDING actions can be executed.
- DNS traffic is forwarded to the Arm for further processing
- Non-DNS traffic is forwarded to the egress port using hairpin

4. Configuration Flow

DPDK initialization.

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            dpdk_init(&argc, &argv, &nb_queues, &nb_ports);

Stateful flow table (SFT) and port initialization.
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            dpdk_ports_init(nb_queues,nb_ports);
        
```
- Mempool allocation
- Rx/Tx and hairpin queue initialization
- DPDK port initialization

Hairpin binding.

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            enable_hairpin_queues(portid, &peer_ports , 1);

Binds hairpin queues for the given port ID

DOCA flow initialization.

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            doca_flow_init(&dns_flow_cfg, &error);

DOCA flow ports initialization.
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            dns_filter_port_init(&port_cfg, portid);
        
```
- Initializes DOCA flow port with the given port configuration for the given port ID.
Note:

DOCA flow port initialization is done for both ports of the BlueField and after the DPDK ports have been initialized.
Non-DNS hairpin traffic.
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```
            
            build_hairpin_pipes(ports[portid], portid, nb_queues);
        
```
- Builds two hairpin pipes, that forward packets to Arm. For a given port, each pipe has one entry for the relevant matching patterns. The first hairpin pipe is for matching UDP non-DNS traffic and the second one is for matching TCP traffic. Note that these pipes are built for both ports of the BlueField.
Build DNS pipe.
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```
            
            build_dns_pipes(ports[portid], portid, nb_queues);
        
```
- Builds DNS pipe for a given port. The built pipe has one entry for matching DNS traffic and forwarding it to Arm.
Processing packets.
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            main_loop(nb_queues, nb_ports);
        
```
- All received packets on Arm, are DNS packets, while non-DNS packets are forwarded to the egress port using hairpin allowing DNS packets to be filtered.

5. Running Application on BlueField

Please refer to the DOCA Installation Guide for details on how to install BlueField related software.
To build the application
1. The DNS filter example is installed as part of the doca-dpi-lib package, the binary is located under /opt/mellanox/doca/examples/dns_filter/bin/doca_dns_filter. To re-build the DNS filter sample, run:
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```
            
            cd /opt/mellanox/doca/examples/dns_filter/src
meson /tmp/build
ninja -C /tmp/build
        
```
  doca_dns_filter will be created under tmp/build.
2. The build process depends on the PKG_CONFIG_PATH environment variable to locate the DPDK libraries. If the variable was accidently corrupted, and the build fails, run the following command:
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    export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/opt/mellanox/dpdk/lib/aarch64-linux-gnu/pkgconfig
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    export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/opt/mellanox/dpdk/lib64/pkgconfig
3. The DNS filter example is a DPDK application. Therefore, the user is required to provide DPDK flags and allocate huge pages. Run:
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            echo 1024 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
        
```
To run the application:
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            ./doca_dns_filter [dpdk flags] -- -l [log_level]
        
```
Note:

SFs must be enabled according to Scalable Function Setup Guide.

For example:
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```
            
            /opt/mellanox/doca/examples/dns_filter/bin/doca_dns_filter -a auxiliary:mlx5_core.sf.4 -a auxiliary:mlx5_core.sf.5 -- -l 3
        
```
Note:

The flag -a auxiliary:mlx5_core.sf.4 -a auxiliary:mlx5_core.sf.5 is a must for proper usage of the application. Modifying this flag will result unexpected behavior as only two ports are supported. The SF number is arbitrary and configurable. For additional information on available flags for DPDK, use -h before the -- separator. For information on available flags for the application, use -h after the -- separator. The -l or –-log_level flag sets the log level for the app (ERR=0, DEBUG=3).

6. Running Application on Host

Please refer to Running Reference Applications Over Host Guide.

7. References

/opt/mellanox/doca/examples/dns_filter/src/dns_filter.c

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