diff --git a/Cargo.lock b/Cargo.lock
index 8aed041db..a1a25d2f8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -582,6 +582,12 @@ version = "3.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c1ad822118d20d2c234f427000d5acc36eabe1e29a348c89b63dd60b13f28e5d"
 
+[[package]]
+name = "by_address"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e245704f60eb4eb45810d65cf14eb54d2eb50a6f3715fe2d7cd01ee905c2944f"
+
 [[package]]
 name = "bytemuck"
 version = "1.12.1"
@@ -3715,6 +3721,7 @@ name = "tor-linkspec"
 version = "0.5.1"
 dependencies = [
  "base64ct",
+ "by_address",
  "cfg-if",
  "derive_builder_fork_arti",
  "derive_more",
diff --git a/crates/tor-linkspec/Cargo.toml b/crates/tor-linkspec/Cargo.toml
index 39828bcd8..fc2653bd5 100644
--- a/crates/tor-linkspec/Cargo.toml
+++ b/crates/tor-linkspec/Cargo.toml
@@ -18,6 +18,7 @@ pt-client = []
 
 [dependencies]
 base64ct = "1.5.1"
+by_address = "1"
 cfg-if = "1.0.0"
 derive_builder = { version = "0.11.2", package = "derive_builder_fork_arti" }
 derive_more = "0.99"
diff --git a/crates/tor-linkspec/src/ids/by_id.rs b/crates/tor-linkspec/src/ids/by_id.rs
index 899e86397..be95a70c3 100644
--- a/crates/tor-linkspec/src/ids/by_id.rs
+++ b/crates/tor-linkspec/src/ids/by_id.rs
@@ -52,9 +52,121 @@ impl<H: HasRelayIds> ByRelayIds<H> {
         self.by_id(any_id)
             .filter(|val| val.has_all_relay_ids_from(key))
     }
+
+    /// Return a reference to every element in this set that shares _any_ ID
+    /// with `key`.
+    ///
+    /// No element is returned more than once.
+    pub fn all_overlapping<T>(&self, key: &T) -> Vec<&H>
+    where
+        T: HasRelayIds,
+    {
+        use by_address::ByAddress;
+        use std::collections::HashSet;
+
+        let mut items: HashSet<ByAddress<&H>> = HashSet::new();
+
+        for ident in key.identities() {
+            if let Some(found) = self.by_id(ident) {
+                items.insert(ByAddress(found));
+            }
+        }
+
+        items.into_iter().map(|by_addr| by_addr.0).collect()
+    }
 }
 
 // TODO MSRV: Remove this `allow` once we no longer get a false positive
 // for it on our MSRV.  1.56 is affected; 1.60 is not.
 #[allow(unreachable_pub)]
 pub use tor_basic_utils::n_key_set::Error as ByRelayIdsError;
+
+#[cfg(test)]
+mod test {
+    #![allow(clippy::unwrap_used)]
+
+    use super::*;
+    use crate::{RelayIds, RelayIdsBuilder};
+
+    #[test]
+    fn lookup() {
+        let rsa1: RsaIdentity = (*b"12345678901234567890").into();
+        let rsa2: RsaIdentity = (*b"abcefghijklmnopqrstu").into();
+        let rsa3: RsaIdentity = (*b"abcefghijklmnopQRSTU").into();
+        let ed1: Ed25519Identity = (*b"12345678901234567890123456789012").into();
+        let ed2: Ed25519Identity = (*b"abcefghijklmnopqrstuvwxyzABCDEFG").into();
+        let ed3: Ed25519Identity = (*b"abcefghijklmnopqrstuvwxyz1234567").into();
+
+        let keys1 = RelayIdsBuilder::default()
+            .rsa_identity(rsa1)
+            .ed_identity(ed1)
+            .build()
+            .unwrap();
+
+        let keys2 = RelayIdsBuilder::default()
+            .rsa_identity(rsa2)
+            .ed_identity(ed2)
+            .build()
+            .unwrap();
+
+        let mut set = ByRelayIds::new();
+        set.insert(keys1.clone());
+        set.insert(keys2.clone());
+
+        // Try by_id
+        assert_eq!(set.by_id(&rsa1), Some(&keys1));
+        assert_eq!(set.by_id(&ed1), Some(&keys1));
+        assert_eq!(set.by_id(&rsa2), Some(&keys2));
+        assert_eq!(set.by_id(&ed2), Some(&keys2));
+        assert_eq!(set.by_id(&rsa3), None);
+        assert_eq!(set.by_id(&ed3), None);
+
+        // Try exact lookup
+        assert_eq!(set.by_all_ids(&keys1), Some(&keys1));
+        assert_eq!(set.by_all_ids(&keys2), Some(&keys2));
+        {
+            let search = RelayIdsBuilder::default()
+                .rsa_identity(rsa1)
+                .build()
+                .unwrap();
+            assert_eq!(set.by_all_ids(&search), Some(&keys1));
+        }
+        {
+            let search = RelayIdsBuilder::default()
+                .rsa_identity(rsa1)
+                .ed_identity(ed2)
+                .build()
+                .unwrap();
+            assert_eq!(set.by_all_ids(&search), None);
+        }
+
+        // Try looking for overlap
+        assert_eq!(set.all_overlapping(&keys1), vec![&keys1]);
+        assert_eq!(set.all_overlapping(&keys2), vec![&keys2]);
+        {
+            let search = RelayIdsBuilder::default()
+                .rsa_identity(rsa1)
+                .ed_identity(ed2)
+                .build()
+                .unwrap();
+            let answer = set.all_overlapping(&search);
+            assert_eq!(answer.len(), 2);
+            assert!(answer.contains(&&keys1));
+            assert!(answer.contains(&&keys2));
+        }
+        {
+            let search = RelayIdsBuilder::default()
+                .rsa_identity(rsa2)
+                .build()
+                .unwrap();
+            assert_eq!(set.all_overlapping(&search), vec![&keys2]);
+        }
+        {
+            let search = RelayIdsBuilder::default()
+                .rsa_identity(rsa3)
+                .build()
+                .unwrap();
+            assert_eq!(set.all_overlapping(&search), Vec::<&RelayIds>::new());
+        }
+    }
+}
diff --git a/crates/tor-linkspec/src/lib.rs b/crates/tor-linkspec/src/lib.rs
index 1c121733a..8ae929523 100644
--- a/crates/tor-linkspec/src/lib.rs
+++ b/crates/tor-linkspec/src/lib.rs
@@ -48,7 +48,10 @@ pub use ids::{
     RelayId, RelayIdError, RelayIdRef, RelayIdType, RelayIdTypeIter,
 };
 pub use ls::LinkSpec;
-pub use owned::{OwnedChanTarget, OwnedChanTargetBuilder, OwnedCircTarget, RelayIds};
+pub use owned::{
+    OwnedChanTarget, OwnedChanTargetBuilder, OwnedCircTarget, OwnedCircTargetBuilder, RelayIds,
+    RelayIdsBuilder,
+};
 pub use traits::{
     ChanTarget, CircTarget, DirectChanMethodsHelper, HasAddrs, HasChanMethod, HasRelayIds,
     HasRelayIdsLegacy,