epoch tag in sync

1 files changed, 4 insertions, 1 deletions

diff --git a/docs/peers.md b/docs/peers.md
index e86e530..7213e70 100644
--- a/docs/peers.md
+++ b/docs/peers.md
@@ -104,7 +104,10 @@ epoch, and lost or stale sync state is repaired by the reply timeout, the `need`
 the heal. Keepalives only inform.
 
 Every message carries the sender's epoch, and with it how many times the sender changed
-epoch in its current run. A node records a peer's epoch only from a message whose count
+epoch in its current run. Sync messages, which go often and only between peers on one
+epoch, carry a tag of it instead: its generation and the first 8 bytes of its ID. The
+receiver takes it for its own epoch, or the sender's as it last knew it, whichever it
+names; one that names neither is dropped. A node records a peer's epoch only from a message whose count
 is at least the newest it has seen from that peer, so a message delayed from before
 the peer switched (or rejoined, or gave up a rejoin) can't flip its recorded epoch
 back. The count starts over when the peer restarts, which its HELLO or HELLO_REPLY