dns-spf-flatten

A Go CLI tool to flatten DNS SPF records and output a list of IP addresses. This tool can be used to convert your SPF records to contain only IP addresses and overcome issues with more than 10 DNS lookups.

Installation

go install github.com/perryh/dns-spf-flatten@latest

Or build from source:

go build -o dns-spf-flatten .

Usage

dns-spf-flatten [options]

Options

• -ip4 value - IPv4 addresses to include (can be specified multiple times)
• -ip6 value - IPv6 addresses to include (can be specified multiple times)
• -include value - Domain names to include SPF records from (can be specified multiple times)
• -tags - List IP addresses with ip4 and ip6 tags

Examples

Flatten SPF records from include domains:

dns-spf-flatten -include gmail.com -include example.com

Combine manual IPs with include domains:

dns-spf-flatten -ip4 192.0.2.1 -ip4 192.0.2.2 -include example.com

Use IPv6 addresses:

dns-spf-flatten -ip6 2001:db8::1 -include example.com

Full example:

$ DNS_RESOLVER=1.1.1.1:53 ./dns-spf-flatten -ip4 1.2.3.4 -ip4 1.2.3.5 -ip6 2001:db8:3333:4444:5555:6666:7777:8888 -ip6 2001:db8:3333:4444:CCCC:DDDD:EEEE:FFFF -include google.com
1.2.3.4
1.2.3.5
2001:db8:3333:4444:5555:6666:7777:8888
2001:db8:3333:4444:CCCC:DDDD:EEEE:FFFF
74.125.0.0/16
209.85.128.0/17
2001:4860:4000::/36
2404:6800:4000::/36
2607:f8b0:4000::/36
2800:3f0:4000::/36
2a00:1450:4000::/36
2c0f:fb50:4000::/36

How It Works

1. Resolves the SPF record (TXT record starting with v=spf1) for each include domain
2. Extracts ip4: and ip6: entries from the SPF record
3. Recursively resolves nested include: entries
4. Combines all discovered IPs with the manually provided -ip4 and -ip6 addresses
5. Deduplicates and outputs the final list of IP addresses

Environment Variables

• DNS_RESOLVER - Custom DNS resolver address (default: 127.0.0.1:53)

Example:

DNS_RESOLVER=8.8.8.8:53 dns-spf-flatten -include example.com