diff --git a/src/protocol.md b/src/protocol.md
index f55ea0b..d038087 100644
--- a/src/protocol.md
+++ b/src/protocol.md
@@ -1,8 +1,9 @@
 # Syndicate Protocol
 
 Actors that share a local [scope](./glossary#scope) can communicate directly. To communicate
-further afield, scopes are *connected* using [relay actors](./glossary.md#relay). Relays allow
-*indirect* communication: distant entities can be addressed as if they were local.
+further afield, scopes are *connected* using [relay
+actors](./glossary.md#relay).[^analogy-to-subnets] Relays allow *indirect* communication:
+distant entities can be addressed as if they were local.
 
 Relays exchange *Syndicate Protocol* messages across a [transport](./glossary.md#transport). A
 *transport* is the underlying medium connecting one relay to its counterparts on a given
@@ -908,6 +909,9 @@ def instantiate(template, bindings):
 
 #### Notes
 
+[^analogy-to-subnets]: Strictly speaking, scope *subnets* are connected by relay actors. The
+    situation is directly analogous to IP subnets being connected by IP routers.
+
 [^relaying-over-syndicate]: In fact, it makes perfect sense to run the relay protocol between
     actors that are *already connected* in some scope: this is like running a VPN, tunnelling
     IP over IP. A variation of the Syndicate Protocol like this gives [federated