ipv6 subnet id extraction: work well with prefix delegations as tiny as /61

Stops requiring a /48 to work with IPv4. Unlike the tunnel broker the native IPv6 connection I'm using only delegates a /56 which seems to be the most common prefix length.

1 files changed, 1 insertions, 8 deletions

diff --git a/src/main.rs b/src/main.rs
index 2dfadfd..839f717 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -355,14 +355,7 @@ fn is_dhcp_known(hostname: &Name, leases: Arc<RwLock<Vec<Lease>>>) -> Result<boo
 fn subnet_id(addr: &IpAddr) -> u8 {
     match addr {
         IpAddr::V4(v4) => v4.octets()[2],
-        IpAddr::V6(v6) => {
-            u16::from_be_bytes(
-                v6.octets()[6..8]
-                    .try_into()
-                    .expect("ipv6 address is less than 8 bytes long, should be 16"),
-            ) as u8
-                * 10
-        }
+        IpAddr::V6(v6) => (v6.octets()[7] & 0x07) * 10, // Max. 8 subnets => assume PD /61.
     }
 }