Xpress DNS is an experimental DNS server written in BPF for high throughput, low latency DNS responses.
It uses eXpress Data Path to process packets early in the Linux networking path.
A user space application is provided to add DNS records to a BPF map which is read from in-kernel by the XDP module.
DNS requests that do not match are passed on to the Linux networking stack.

Xpress DNS could be used as a high performance DNS proxy for common DNS requests of static DNS records.
By responding to DNS requests before the packet gets processed by the Linux networking stack, it alleviates load on the system and DNS servers in user space.

• Currently supports A records
• Only supports plain DNS over UDP (port 53)
• Basic EDNS implementation
• Only responds to single queries for now
• No recursive lookups

• Kernel version 5.8 or higher is required as this program uses the bpf_xdp_adjust_tail call to extend packet size. See https://lwn.net/Articles/820562/, merged in 5.8.
• iproute2 to load the BPF object on a network device

To build this software we use Docker to ensure a reproducable build environment.
With Docker installed, run the make command in the root of the repository.

To build the software without Docker: install llvm, clang, libbpf-dev, iproute2 and run the make command in the src directory.

Load the xdp_dns_kern.o BPF object using iproute2 on the target network interface (veth0 in the example below):

ip link set dev veth0 xdp obj ./src/xdp_dns_kern.o

Use the xdns user space application to manage DNS records.

Usage: xdns add record_type domain_name value [ttl]
       xdns remove record_type domain_name value
       xdns list

Example: xdns add a foo.bar 127.0.0.1 120

Use xdns list to list all configured DNS records.

Xpress DNS is compatible with BCC toolkit and can be instrumented with its Python bindings.
You can refer to the supplied unit tests in test_xdp_dns.py for pointers on how to test the code using BCC, scapy and Python's unit test module. Run make test in the root directory to run the supplied unit tests.

Build with make DEBUG=y to enable debug logging, which logs debug information to /sys/kernel/debug/tracing/trace_pipe

This repository is licensed under GPLv2.0. See LICENSE file for details.