From cfb0287c28f5f58f768a4f69b7694cf974420109 Mon Sep 17 00:00:00 2001
From: blockchaindevsh <shore.cloud@gmail.com>
Date: Tue, 16 Dec 2025 11:41:23 +0800
Subject: [PATCH] add chainid to op-geth ENR

---
 eth/backend.go                         |  2 ++
 eth/protocols/eth/discovery_chainid.go | 39 ++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 eth/protocols/eth/discovery_chainid.go

diff --git a/eth/backend.go b/eth/backend.go
index 5bbc5fc757..7444b33259 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -610,6 +610,8 @@ func (s *Ethereum) updateFilterMapsHeads() {
 
 func (s *Ethereum) setupDiscovery() error {
 	eth.StartENRUpdater(s.blockchain, s.p2pServer.LocalNode())
+	// Set chainID ENR entry
+	eth.SetChainIDENR(s.p2pServer.LocalNode(), s.blockchain.Config())
 
 	// Add eth nodes from DNS.
 	dnsclient := dnsdisc.NewClient(dnsdisc.Config{})
diff --git a/eth/protocols/eth/discovery_chainid.go b/eth/protocols/eth/discovery_chainid.go
new file mode 100644
index 0000000000..67b9608b0f
--- /dev/null
+++ b/eth/protocols/eth/discovery_chainid.go
@@ -0,0 +1,39 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package eth
+
+import (
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+// ChainIDEntry is the ENR entry which advertises the chain ID on discovery.
+type ChainIDEntry uint64
+
+// ENRKey implements enr.Entry.
+func (e ChainIDEntry) ENRKey() string {
+	return "chainID"
+}
+
+// SetChainIDENR sets the chainID ENR entry on the local node.
+func SetChainIDENR(ln *enode.LocalNode, cfg *params.ChainConfig) {
+	if cfg == nil || cfg.ChainID == nil {
+		return
+	}
+	entry := ChainIDEntry(cfg.ChainID.Uint64())
+	ln.Set(&entry)
+}