The bitcoind client has a -maxconnections configuration option. Setting -maxconnections=N specifies the total number of connections, including both incoming and ourbound connections (the default is 125, 8 outbound and 117 inbound)

Nodes are identified by their IP addresses. If a node misbehaves => it gets added to its "ban list" => so it won’t listen to that node anymore (The more people that "ban" that node, the less effect it has on the network)

Misbehaving includes things like spamming mempool messages, relaying invalid transactions, and broadcasting invalid blocks (Reference: https://bitcoin.stackexchange.com/questions/48834#48835)