There is a overlap with this submit and others however I will attempt to immediately right a few issues right here.
Why do we’ve two varieties of connections, outgoing and incoming?
To threat stating the plain typically our node will make a request to connect with one other node (outbound) while different instances a node will make a request to connect with our node (inbound). In a wholesome peer to look (P2P) protocol you possibly can’t actually keep away from having each outgoing and incoming requests. The extent to which outbound and inbound connections are handled otherwise by your full node is a extra fascinating query. These Bitcoin Core PR evaluate membership notes (June eighth 2022) on inbound block-relay-only connections acknowledged:
As soon as the connection is established, the connection is essentially symmetric (the protocol works the identical in each instructions), though we deal with outbound friends with some desire.
If you’re involved about malicious full nodes you might need some trusted or semi trusted full nodes you select to connect with (outbound) while presumably all inbound connection requests are from nodes you realize little or no about.
Are outgoing connections those the place we notify of latest blocks/transactions, whereas incoming connections are those the place they notify us of latest blocks/transactions?
No, each outbound and inbound connections can notify your node of latest blocks and transactions and vice versa. That PR evaluate membership I referred to does talk about block-relay-only friends which is the place you resolve to solely relay blocks to sure friends and never transactions, IP addresses. Inbound connections also can point out they do not wish to obtain transactions and so on.
Once we do the preliminary synchronization (IBD) or utterly randomly wish to ask a couple of block or transaction or one thing third, is it completed with outgoing connections or incoming connections?
Each. If we aren’t conscious of any friends/connections (ie we’ve no connections in any respect) originally of IBD we would must make the most of DNS seeds to be taught of potential friends.
edit: Because of lightlike for declaring this remark within the Bitcoin Core code on IBD normally solely being completed with outbound friends
If we haven’t any outbound
friends, or if we aren’t downloading any blocks from such friends, then
permit block downloads from this peer, too. We choose downloading
blocks from outbound friends to keep away from placing undue load on (say) some
house person who’s simply making outbound connections to the community, however
if our solely supply of the newest blocks is from an inbound peer, we
need to you’ll want to finally obtain it (and never simply wait
indefinitely for an outbound peer to have it).