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While setting up the Monero GUI with a Ledger nano S, I did not enter anything in the 'optional fields' in the GUI.

The guide on the Ledger support website states:

Enter 1720000 in the restore height field, then enter 3:100 in the subaddress lookahead field

I don't remember doing this (because I did not enter anything where the Monero GUI said 'optional').

Is it necessary to enter a restore height, and if you did not, what are the consequences?

And is it also necessary to enter a subaddress lookahead field? If i did not, because it's stated as 'optional' in the GUI, what are the consequences?

Thanks for your help!

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When you restore a wallet from seed, you scan the blockchain to attempt to decrypt the destination of each transaction, to see if any of those transactions were destined for you. This process will discover which amounts of Monero (a.k.a. outputs) are owned by your wallet.

If you know you had not received any funds prior to a certain date, you can save time by only scanning the blockchain from a more recent point in time. Block 1720000 was created on 2018-12-05 (see https://xmrchain.net/block/1720000), so if you restored from this height you would not see any funds in your wallet that arrived prior to that date.

The default subaddress lookahead is 50:200, which means creating a lookup table of 50 accounts with 200 subaddresses each, totalling 50*200=10000 subaddresses to scan for initially. Generating this lookup table requires computation, so by reducing the number you initially scan for, you can reduce the Ledger setup time. This is mentioned here: https://github.com/LedgerHQ/ledger-app-monero/blob/master/doc/user/bolos-app-monero.rst

By reducing the lookahead to 3:100, this means that if you'd created 4 accounts and received funds to the 4th account but not to the first 3, the Ledger would not notice any of the funds received to account 4 when scanning. Similarly, if you'd created 101 subaddresses in the first account, received funds to subaddress 101 but not to any of the first 100, then the Ledger would not notice the funds that arrived at subaddress 101. But if you had received funds at subaddresses 90 and 101, then when Ledger saw the incoming funds at subaddress 90 it would then automatically start scanning further ahead by another 100 subaddresses in the future, so that it doesn't miss incoming funds. For more information, see Funds received from subwallet are not showing

TL;DR: By specifying a restore height and smaller lookahead range, you decrease the computation required by the Ledger and can therefore restore your wallet faster. This comes at the risk of the Ledger missing incoming funds if you are restoring a very old wallet or if your subaddress usage pattern is such that you issue lots of unused subaddresses.

  • Thank you for the information! Now I understand it! So the restore height is only important at the moment I want to open my Monero GUI again, and i want to scan the blocks that would hold any of my transaction. As I did my first transfer this week, I should add like '1830000' and I should be fine. What comes to the subadress lookahead, I did nothing wrong with just letting stand the default ratio - only that it will take longer to scan for my transactions? – xavsky May 18 at 13:16
  • "So the restore height is only important at the moment I want to open my Monero GUI again" <- No. It only has a bearing on restoring, not opening the GUI. – jtgrassie May 18 at 13:25
  • Edit "What comes to the subadress lookahead, I did nothing wrong with just letting stand the default ratio - only that it will take longer to scan for my transactions?" --> or is it just that creating the wallet took longer? – xavsky May 18 at 13:26
  • @xavsky The subaddress lookup table is a one-time cost, and mostly not an ongoing cost. Therefore I'd personally not bother with reducing it, because I don't mind initial extra setup time. It's only a problem if you issue lots of subaddresses and don't use many of them. If this turns out to be the case, you can always restore your wallet again using a different lookahead rule. Also, the Ledger will always know about transactions you make on it. So the rule makes no difference except when restoring or when noticing funds received via subaddresses created via a different wallet. – knaccc May 18 at 13:38
  • Thank you so much for this information! Now I am reassured about both settings! :-) Have a nice day! – xavsky May 18 at 15:15

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