public boolean checkForkId(final DiscoveryPeer peer) {
    return peer.getForkId().map(forkIdManager::peerCheck).orElse(true);
  }
The peer discovery agent is the network component that sends and receives peer discovery messages
via UDP.
ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/discovery/PeerDiscoveryAgent.java