eth\/66<\/span><\/a> protocol is a fairly small change, yet has quite a number of beneficial implications. In short, the protocol introduces request and reply IDs for all bidirectional packets. The goal behind these IDs is to more easily match up responses to requests, specifically, to more easily deliver a response to a subsystem that made the original request.<\/p>\nThese IDs are not essential, and indeed we’ve been happily working around the lack of them these past 6 years. Unfortunately, all code that needs to request anything from the network becomes overly complicated, if multiple subsystems can request the same type of data concurrently. E.g. block headers can be requested by the downloader<\/em> syncing the chain; it can be requested by the fetcher<\/em> fulfilling block announcements; and it can be requested by fork challenges. Furthermore, timeouts can cause late\/unexpected deliveries or re-requests. In all these cases, when a header packet<\/em> arrives, every subsystem peeks at the data and tries to figure out if it was meant for itself or someone else. Consuming a reply not meant for a particular subsystem will cause a failure elsewhere, which needs graceful handling. It just gets messy. Doable, but messy.<\/p>\nThe importance of eth\/66<\/span> in the scope of this blog post is not that it solves a particular problem, rather that it is introduced prior to the Berlin hard-fork<\/strong>. As all nodes are expected to upgrade by the fork time, this means Geth can start deprecating the old protocols after the fork. Only after discontinuing all older protocols can we rewrite Geth’s internals to take advantage of request ids. Following our protocol deprecation schedule<\/a>, we’ll be dropping eth\/64<\/span> shortly and eth65<\/span> by the end of summer.<\/p>\nSome people might consider Geth using its weight to force protocol updates on other clients. We’d like to emphasize that the typed transactions<\/a> feature from the Berlin hard-fork originally called for a new protocol version. As only Geth implemented the full suite of eth\/xy<\/span> protocols, other clients requested “hacking” it into old protocol versions to avoid having to focus on networking at this time. The agreement was that Geth backports typed transaction support into all its old protocol code to buy other devs time, but in exchange will phase out the old versions in 6 months to avoid stagnation.<\/em><\/p>\n