The Network Time Protocol (NTP) is widely used to synchronize computer clocks. The Precision Time Protocol (PTP) can be used as a time source as well, which is expected to be accurate within microseconds. However, at Microsoft Azure VMs, PTP-derived time-of-day errors could exceed 50,000 microseconds, which may be inadequate. Let’s go into some details:
For some reason, I came across a blog post by Gian Paolo called Small servers. This reminded me of some fairly old network protocols (that no one uses as far as I know) that are not in my Ultimate PCAP yet. Hence I took some minutes, captured them, and took some Wireshark screenshots. They are: echo, discard, daytime, chargen, and time. Mostly via TCP and UDP, and, as you would have expected, IPv6 and legacy IP.
I’m aware that this is not of interest to most of you. :) But for the sake of completeness, and because I love adding new protocols to the Ultimate PCAP, I added them though.
NTP (Network Time Protocol) messages are sometimes rate-limited or blocked entirely by Internet operators. This little-known “NTP filtering” was put into place several years ago in response to DDoS (Distributed Denial of Service) attacks. NTP filtering may drop NTP messages based on rate or message size. Let’s dig into it: Continue reading NTP Filtering (Delay & Blockage) in the Internet