Private Ethereum blockchain does not sync last 65 block

Question

I've successfully create a private Ethereum network, I've two machines on the same local network, the first one is where I've created the chain, the second should be a new peer that should sync with the first one. Everything works fine, addPeer correctly works and I can see the two nodes in the netowrk, but the second node when trying to sync the blockchain stuck at block 5574 of 5839.

As I can see online is a quite common problem, but I cannot find a solution regarding private ethereum network. I've already tried --syncmode fast but does not help.

EDIT:

I've tried to mine with the first node, and the second start to sync the blockchain again, but it stucks always at 65 blocks to the end.

This is what eth.syncing says every time:

{
  currentBlock: 5789,
  highestBlock: 5854,
  knownStates: 8,
  pulledStates: 8,
  startingBlock: 5789
}

Now the last node in my blockchain is 5854, but the second node stop syncing at 5789.

This is instead what loop in the console:

INFO [08-12|11:15:42.672] Imported new block headers               count=0 elapsed=6.452ms  number=5854 hash=776928…4288ca ignored=65
WARN [08-12|11:15:42.767] Node data write error                    err="state node a736c3…a6fb08 failed with all peers (1 tries, 1 peers)"
WARN [08-12|11:15:42.842] Synchronisation failed, retrying         err="state node a736c3…a6fb08 failed with all peers (1 tries, 1 peers)"

Please help, I really cannot find a solution, thank you.

EDIT 2:

I suppose the the issue is in the genesis file. I've recreated the chain with a new genesis file, this is the old one:

{
    "config": {
        "chainId": 77,
        "homesteadBlock": 0,
        "eip155Block": 0,
        "eip158Block": 0
    },
    "difficulty": "0x20",
    "gasLimit": "0x2100000",
    "alloc": {
        "8b06011b54a70f2a5a674a3bc24b81d0792dc941": 
         { "balance": "0x1337000000000000000000" }     
    }
}

This is the new one generated with puppeth:

{
  "config": {
    "chainId": 77,
    "homesteadBlock": 0,
    "eip150Block": 0,
    "eip150Hash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "eip155Block": 0,
    "eip158Block": 0,
    "byzantiumBlock": 0,
    "ethash": {}
  },
  "nonce": "0x0",
  "timestamp": "0x5b7000cc",
  "extraData": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "gasLimit": "0x47b760",
  "difficulty": "0x80000",
  "mixHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "coinbase": "0x0000000000000000000000000000000000000000",
  "alloc": {
    "0000000000000000000000000000000000000000": {
      "balance": "0x1"
    },
    "0000000000000000000000000000000000000001": {
      "balance": "0x1"
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Every chain generated with first genesis file fails during sync across peers, but with the second one no. Anyone knows why?

Answer 1

The problem is in the genesis file. In the first genesis json I've not specified the extraData field. This cause that the first block of the chain has a strange value in its extraData field.

Here is what happens if in the genesis json there isn't:

{
  difficulty: 32,
  extraData: "0x",
  gasLimit: 34603008,
  gasUsed: 0,
  hash: "0x2066362553ef96616831d4cd2b5d83a094c8a8d5a72075c54b2533adf9b7f0cf",
  logsBloom: "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  miner: "0x0000000000000000000000000000000000000000",
  mixHash: "0x0000000000000000000000000000000000000000000000000000000000000000",
  nonce: "0x0000000000000000",
  number: 0,
  parentHash: "0x0000000000000000000000000000000000000000000000000000000000000000",
  receiptsRoot: "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
  sha3Uncles: "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
  size: 537,
  stateRoot: "0x628cb5c97b5614e02d6fda3b0684f7464cb933c4cb5e09e2d74b56963db036d4",
  timestamp: 0,
  totalDifficulty: 32,
  transactions: [],
  transactionsRoot: "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
  uncles: []
}

0x is not a number. This cause the issue, because if I add this line in the genesis file:

"extraData": "0x0000000000000000000000000000000000000000000000000000000000000000",

The syncing problem disappear.