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Limit allowed private address space to avoid long CIDR strings #215

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Merged
edi-oai merged 1 commit into from
Oct 9, 2026
Merged

Limit allowed private address space to avoid long CIDR strings #215

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10 changes: 8 additions & 2 deletions lib/subnet_finder/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,13 +8,19 @@ const MAX_ATTEMPTS: usize = 128;

/// Find an available private subnet and its first two usable host addresses
pub(crate) fn find_available_subnet(prefix_len: u8) -> Result<(Ipv4Addr, Ipv4Addr, Ipv4Net)> {
// Add private address space (as defined in RFC 1918[1])
// Add private address space (as defined in RFC 1918[1]) with one exception
//
// We narrow the 192.168.0.0/16 allocation pool to work around a macOS bug
// where long subnet address strings lose their CIDR prefix in the generated
// firewall rules, causing connection issues.
//
// [1]: https://datatracker.ietf.org/doc/html/rfc1918#section-3
let private_subnets: Vec<Ipv4Net> = vec![
"10.0.0.0/8".parse()?,
"172.16.0.0/12".parse()?,
"192.168.0.0/16".parse()?,
"192.168.0.0/18".parse()?, // third octet 0–63
"192.168.64.0/19".parse()?, // third octet 64–95
"192.168.96.0/22".parse()?, // third octet 96–99
];

// Figure out which address space is already utilized on the host
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