[feature] RFC-compliant multicast MAC derivation

Implements multicast MAC address derivation from IP addresses following RFC standards:
  - IPv4: RFC 1112 Section 6.4 (01:00:5e prefix + 23 bits)
  - IPv6: RFC 2464 Section 7 (33:33 prefix + 32 bits)

  Features:
  - Core trait returns [u8; 6] for dependency-light usage
  - Optional macaddr feature provides MacAddr6 integration
  - Support for IpAddr, Ipv4Addr, Ipv6Addr, and IpNetwork types
  - Comprehensive tests with RFC compliance verification

We need this in both dendrite (testing) and omicron.
It felt proper to place this here over omicron common (for example).

Author: zeeshanlakhani

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [0.2.0] - 2025-07-18
+
+* Adds `MulticastMac` trait for deriving multicast MAC addresses from IP addresses
+* Implements RFC 1112 (IPv4) and RFC 2464 (IPv6) multicast MAC derivation
+* Optional `macaddr` feature for `MacAddr6` integration
+
 ## [0.1.2] - 2025-05-25
 
 * Bumps Rust min-version to 1.84 for direct `is_unique_local` call on IPv6

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "oxnet"
-version = "0.1.2"
+version = "0.2.0"
 edition = "2021"
 rust-version = "1.84.0"
 license = "MIT OR Apache-2.0"
@@ -14,6 +14,7 @@ categories = ["network-programming", "web-programming"]
 [features]
 default = ["serde", "schemars", "ipnetwork"]
 ipnetwork = ["dep:ipnetwork"]
+macaddr = ["dep:macaddr"]
 schemars = ["dep:schemars", "dep:serde_json"]
 serde = ["dep:serde"]
 std = []
@@ -23,6 +24,7 @@ schemars = {version = "0.8.22", optional = true }
 serde = { version = "1.0.219", optional = true }
 serde_json = { version = "1.0.140", optional = true }
 ipnetwork = { version = "0.21.1", optional = true }
+macaddr = { version = "1.0", optional = true }
 
 [dev-dependencies]
 expectorate = "1.2.0"

Cargo.toml

@@ -5,10 +5,12 @@
 #![doc = include_str!("../README.md")]
 
 mod ipnet;
+mod multicast;
 #[cfg(feature = "schemars")]
 mod schema_util;
 
 pub use ipnet::{
     IpNet, IpNetParseError, IpNetPrefixError, Ipv4Net, Ipv6Net, IPV4_NET_WIDTH_MAX,
     IPV6_NET_WIDTH_MAX,
 };
+pub use multicast::MulticastMac;