I have two clusters that have the same replSet name and keyFile, for example: CLUSTER_A： ydmongo:PRIMARY> rs.status() {         "set" : "ydmongo",         ...         "members" : [                 {                         "_id" : 0,                         "name" : "192.168.111.10:21000",                         "health" : 1,                         "state" : 1,                         "stateStr" : "PRIMARY",                         ...                 },                 {                         "_id" : 1,                         "name" : "192.168.111.10:22000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 },                 {                         "_id" : 2,                         "name" : "192.168.111.10:23000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 }         ],         ... } CLUSTER_B: ydmongo:PRIMARY> rs.status() {         "set" : "ydmongo",         ...         "members" : [                 {                         "_id" : 0,                         "name" : "192.168.111.10:11000",                         "health" : 1,                         "state" : 1,                         "stateStr" : "PRIMARY",                         ...                 },                 {                         "_id" : 1,                         "name" : "192.168.111.10:12000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 },                 {                         "_id" : 2,                         "name" : "192.168.111.10:13000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 }         ],         ... } Now, I add the node in CLUSTER_B to CLUSTER_A, and it returns success ydmongo:PRIMARY> rs.add(\{host:"192.168.111.10:22000"}) {         "ok" : 1,         "$clusterTime" : {                 "clusterTime" : Timestamp(1684195464, 1),                 "signature" : {                         "hash" : BinData(0,"6aQiJetFIK4SAwtd9a+Hx+LxvGk="),                         "keyId" : NumberLong("7233562191683649540")                 }         },         "operationTime" : Timestamp(1684195464, 1) } ydmongo:PRIMARY> rs.status() {         "set" : "ydmongo",         ...         "members" : [                 {                         "_id" : 0,                         "name" : "192.168.111.10:11000",                         "health" : 1,                         "state" : 1,                         "stateStr" : "PRIMARY",                         ...                 },                 {                         "_id" : 1,                         "name" : "192.168.111.10:12000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 },                 {                         "_id" : 2,                         "name" : "192.168.111.10:13000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 },                 {                         "_id" : 3,                         "name" : "192.168.111.10:22000",                         "health" : 0,                         "state" : 8,                         "stateStr" : "(not reachable/healthy)",                         ...                 }         ],         .. } The related content displayed in the log is CLUSTER_A 2023-05-16T08:04:24.730+0800 I  REPL     [conn28] replSetReconfig admin command received from client; new config: { _id: "ydmongo", version: 4, protocolVersion: 1, writeConcernMajorityJo urnalDefault: true, members: [ \{ _id: 0, host: "192.168.111.10:11000", arbiterOnly: false, buildIndexes: true, hidden: false, priority: 1.0, tags: {}, slaveDelay: 0, votes: 1 }, { _id: 1 , host: "192.168.111.10:12000", arbiterOnly: false, buildIndexes: true, hidden: false, priority: 1.0, tags: {}, slaveDelay: 0, votes: 1 }, { _id: 2, host: "192.168.111.10:13000", arbiter Only: false, buildIndexes: true, hidden: false, priority: 1.0, tags: {}, slaveDelay: 0, votes: 1 }, \{ host: "192.168.111.10:22000", _id: 3.0 } ], settings: { chainingAllowed: true, heart beatIntervalMillis: 2000, heartbeatTimeoutSecs: 10, electionTimeoutMillis: 10000, catchUpTimeoutMillis: -1, catchUpTakeoverDelayMillis: 30000, getLastErrorModes: {}, getLastErrorDefaults : \{ w: 1, wtimeout: 0 }, replicaSetId: ObjectId('6462c67d1c82d8f677e4e92d') } } 2023-05-16T08:04:24.865+0800 I  REPL     [conn28] Scheduling remote command request for reconfig quorum check: RemoteCommand 481 -- target:192.168.111.10:22000 db:admin cmd:{ replSetHear tbeat: "ydmongo", configVersion: 4, hbv: 1, from: "192.168.111.10:11000", fromId: 0, term: 1 } 2023-05-16T08:04:24.865+0800 I  CONNPOOL [Replication] Connecting to 192.168.111.10:22000 2023-05-16T08:04:24.866+0800 I  REPL     [conn28] New replica set config in use: { _id: "ydmongo", version: 4, protocolVersion: 1, writeConcernMajorityJournalDefault: true, members: [ {  _id: 0, host: "192.168.111.10:11000", arbiterOnly: false, buildIndexes: true, hidden: false, priority: 1.0, tags: {}, slaveDelay: 0, votes: 1 }, { _id: 1, host: "192.168.111.10:12000", a rbiterOnly: false, buildIndexes: true, hidden: false, priority: 1.0, tags: {}, slaveDelay: 0, votes: 1 }, { _id: 2, host: "192.168.111.10:13000", arbiterOnly: false, buildIndexes: true,  hidden: false, priority: 1.0, tags: {}, slaveDelay: 0, votes: 1 }, \{ _id: 3, host: "192.168.111.10:22000", arbiterOnly: false, buildIndexes: true, hidden: false, priority: 1.0, tags: {},  slaveDelay: 0, votes: 1 } ], settings: { chainingAllowed: true, heartbeatIntervalMillis: 2000, heartbeatTimeoutSecs: 10, electionTimeoutMillis: 10000, catchUpTimeoutMillis: -1, catchUpT akeoverDelayMillis: 30000, getLastErrorModes: {}, getLastErrorDefaults: \{ w: 1, wtimeout: 0 }, replicaSetId: ObjectId('6462c67d1c82d8f677e4e92d') } } 2023-05-16T08:04:24.953+0800 I  REPL_HB  [replexec-7] Heartbeat to 192.168.111.10:22000 failed after 2 retries, response status: InvalidReplicaSetConfig: replica set IDs do not match, ou rs: 6462c67d1c82d8f677e4e92d; remote node's: 6462c6d5b1e1bdd62920f68d 2023-05-16T08:04:24.953+0800 I  REPL     [replexec-7] Member 192.168.111.10:22000 is now in state RS_DOWN - replica set IDs do not match, ours: 6462c67d1c82d8f677e4e92d; remote node's: 6 462c6d5b1e1bdd62920f68d 2023-05-16T08:04:26.954+0800 I  REPL_HB  [replexec-5] Heartbeat to 192.168.111.10:22000 failed after 2 retries, response status: InvalidReplicaSetConfig: replica set IDs do not match, ou rs: 6462c67d1c82d8f677e4e92d; remote node's: 6462c6d5b1e1bdd62920f68d 2023-05-16T08:04:28.955+0800 I  REPL_HB  [replexec-2] Heartbeat to 192.168.111.10:22000 failed after 2 retries, response status: InvalidReplicaSetConfig: replica set IDs do not match, ou rs: 6462c67d1c82d8f677e4e92d; remote node's: 6462c6d5b1e1bdd62920f68d CLUSTER_B 2023-05-16T08:04:23.949+0800 I  ACCESS   [conn23] Successfully authenticated as principal __system on local from client 192.168.111.10:36978 2023-05-16T08:04:23.949+0800 I  ACCESS   [conn22] Successfully authenticated as principal __system on local from client 192.168.111.10:36976 2023-05-16T08:04:23.995+0800 I  ACCESS   [conn22] Successfully authenticated as principal __system on local from client 192.168.111.10:36976 2023-05-16T08:04:24.048+0800 I  ACCESS   [conn22] Successfully authenticated as principal __system on local from client 192.168.111.10:36976 2023-05-16T08:04:24.092+0800 I  ACCESS   [conn22] Successfully authenticated as principal __system on local from client 192.168.111.10:36976 2023-05-16T08:04:28.280+0800 I  ACCESS   [conn25] Successfully authenticated as principal __system on local from client 192.168.111.10:36986 2023-05-16T08:04:28.281+0800 I  ACCESS   [conn26] Successfully authenticated as principal __system on local from client 192.168.111.10:36988 2023-05-16T08:04:28.330+0800 I  ACCESS   [conn25] Successfully authenticated as principal __system on local from client 192.168.111.10:36986 2023-05-16T08:04:28.378+0800 I  ACCESS   [conn25] Successfully authenticated as principal __system on local from client 192.168.111.10:36986 2023-05-16T08:04:28.426+0800 I  ACCESS   [conn25] Successfully authenticated as principal __system on local from client 192.168.111.10:36986 Meanwhile, the result of db.isMaster() is CLUSTER_A: ydmongo:PRIMARY> db.isMaster() {         "hosts" : [                 "192.168.111.10:11000",                 "192.168.111.10:12000",                 "192.168.111.10:13000",                 "192.168.111.10:22000"         ],         "setName" : "ydmongo",         "setVersion" : 4,         "ismaster" : true,         "secondary" : false,         "primary" : "192.168.111.10:11000",         "me" : "192.168.111.10:11000",         ... } CLUSTER_B ydmongo:PRIMARY> db.isMaster() {         "hosts" : [                 "192.168.111.10:21000",                 "192.168.111.10:22000",                 "192.168.111.10:23000"         ],         "setName" : "ydmongo",         "setVersion" : 3,         "ismaster" : true,         "secondary" : false,         "primary" : "192.168.111.10:21000",         "me" : "192.168.111.10:21000",         ... } Now I'm going to add the primary node of CLUSTER_B to CLUSTER_A ydmongo:PRIMARY> rs.add(\{host:"192.168.111.10:21000"}) {         "ok" : 1,         "$clusterTime" : {                 "clusterTime" : Timestamp(1684195779, 2),                 "signature" : {                         "hash" : BinData(0,"vT+HNT9PPsdYcxzNPNCpPF1WlLE="),                         "keyId" : NumberLong("7233562191683649540")                 }         },         "operationTime" : Timestamp(1684195779, 2) } ydmongo:PRIMARY> rs.status() {         "set" : "ydmongo",         ...         "members" : [                 {                         "_id" : 0,                         "name" : "192.168.111.10:11000",                         "health" : 1,                         "state" : 1,                         "stateStr" : "PRIMARY",                         ...                 },                 {                         "_id" : 1,                         "name" : "192.168.111.10:12000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 },                 {                         "_id" : 2,                         "name" : "192.168.111.10:13000",                         "health" : 1,                         "state" : 2,                         "stateStr" : "SECONDARY",                         ...                 },                 {                         "_id" : 3,                         "name" : "192.168.111.10:22000",                         "health" : 0,                         "state" : 8,                         "stateStr" : "(not reachable/healthy)",                         ...                 },                 {                         "_id" : 4,                         "name" : "192.168.111.10:21000",                         "health" : 0,                         "state" : 8,                         "stateStr" : "(not reachable/healthy)",                         ...                 }         ],         ... } ydmongo:PRIMARY> db.isMaster() {         "hosts" : [                 "192.168.111.10:11000",                 "192.168.111.10:12000",                 "192.168.111.10:13000",                 "192.168.111.10:22000",                 "192.168.111.10:21000"         ],         "setName" : "ydmongo",         "setVersion" : 5,         "ismaster" : true,         "secondary" : false,         "primary" : "192.168.111.10:11000",         "me" : "192.168.111.10:11000",         ... } From the official documentation, we learn that the driver detects the replica set topology via db.isMaster(). 【 https://www.mongodb.com/docs/v4.2/reference/command/isMaster/ 】 As a result, connections from CLUSTER_A may be diverted to CLUSTER_B   JUST LIKE THIS: {color:#101214}[INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:05,555]|@|[org.mongodb.driver.cluster]|@|[]|@|Monitor thread successfully connected to server with description ServerDescription\{address=10.100.3.220:28020, type=REPLICA_SET_SECONDARY, state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 2, 8]}, minWireVersion=0, maxWireVersion=8, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=1166127, setName='ydmongo', canonicalAddress=10.100.3.220:28020, hosts=[10.100.3.220:28020, 10.223.209.56:28022, 10.100.3.221:28021, 10.100.3.222:28022], passives=[], arbiters=[], primary='10.100.3.221:28021', tagSet=TagSet\{[]}, electionId=null, setVersion=4, lastWriteDate=Fri May 12 15:24:05 CST 2023, lastUpdateTimeNanos=66032399775199055}|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:06,979]|@|[org.mongodb.driver.cluster]|@|[]|@|Monitor thread successfully connected to server with description ServerDescription\{address=10.100.3.222:28022, type=REPLICA_SET_SECONDARY, state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 2, 8]}, minWireVersion=0, maxWireVersion=8, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=948119, setName='ydmongo', canonicalAddress=10.100.3.222:28022, hosts=[10.100.3.220:28020, 10.223.209.56:28022, 10.100.3.221:28021, 10.100.3.222:28022], passives=[], arbiters=[], primary='10.100.3.221:28021', tagSet=TagSet\{[]}, electionId=null, setVersion=4, lastWriteDate=Fri May 12 15:24:06 CST 2023, lastUpdateTimeNanos=66032401200132431}|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,374]|@|[org.mongodb.driver.cluster]|@|[]|@|Monitor thread successfully connected to server with description ServerDescription\{address=10.100.3.221:28021, type=REPLICA_SET_PRIMARY, state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 2, 8]}, minWireVersion=0, maxWireVersion=8, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=959352, setName='ydmongo', canonicalAddress=10.100.3.221:28021, hosts=[10.100.3.220:28020, 10.223.209.56:28022, 10.100.3.221:28021, 10.100.3.222:28022], passives=[], arbiters=[], primary='10.100.3.221:28021', tagSet=TagSet\{[]}, electionId=7fffffff0000000000000054, setVersion=4, lastWriteDate=Fri May 12 15:24:06 CST 2023, lastUpdateTimeNanos=66032401594541213}|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,374]|@|[org.mongodb.driver.cluster]|@|[]|@|Adding discovered server 10.223.209.56:28022 to client view of cluster|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,375]|@|[org.mongodb.driver.cluster]|@|[]|@|Setting max set version to 4 from replica set primary 10.100.3.221:28021|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,379]|@|[org.mongodb.driver.connection]|@|[]|@|Opened connection [connectionId\{localValue:10, serverValue:162}] to 10.223.209.56:28022|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,381]|@|[org.mongodb.driver.cluster]|@|[]|@|Monitor thread successfully connected to server with description ServerDescription\{address=10.223.209.56:28022, type=REPLICA_SET_PRIMARY, state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 2, 8]}, minWireVersion=0, maxWireVersion=8, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=920667, setName='ydmongo', canonicalAddress=10.223.209.56:28022, hosts=[10.223.209.56:28022, 10.223.209.54:28020, 10.223.209.55:28021], passives=[], arbiters=[], primary='10.223.209.56:28022', tagSet=TagSet\{[]}, electionId=7fffffff0000000000000004, setVersion=1, lastWriteDate=Fri May 12 15:24:06 CST 2023, lastUpdateTimeNanos=66032401601568290}|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,381]|@|[org.mongodb.driver.cluster]|@|[]|@|Adding discovered server 10.223.209.54:28020 to client view of cluster|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,381]|@|[org.mongodb.driver.cluster]|@|[]|@|Adding discovered server 10.223.209.55:28021 to client view of cluster|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,381]|@|[org.mongodb.driver.cluster]|@|[]|@|Server 10.100.3.220:28020 is no longer a member of the replica set.  Removing from client view of cluster.|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,382]|@|[org.mongodb.driver.cluster]|@|[]|@|Server 10.100.3.221:28021 is no longer a member of the replica set.  Removing from client view of cluster.|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,384]|@|[org.mongodb.driver.connection]|@|[]|@|Closed connection [connectionId\{localValue:5, serverValue:1843726}] to 10.100.3.221:28021 because the pool has been closed.|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,384]|@|[org.mongodb.driver.connection]|@|[]|@|Closed connection [connectionId\{localValue:7, serverValue:1850541}] to 10.100.3.221:28021 because the pool has been closed.|@| [INFO ]|@|[]|@|[]|@|[2023-05-12 15:24:07,384]|@|[org.mongodb.driver.connection]|@|[]|@|Closed connection [connectionId\{localValue:4, serverValue:1842210}] to 10.100.3.221:28021 because the pool has been closed.|@|{color} We know that this is abnormal   Hope to receive your reply soon, thank you.