Mail servers typically resolve a remote IP to a PTR. High number of PTR requests can indicate that the network is used to send email. Amazon (both SES and EC2) is one of the biggest email sources on the Internet (ranging from ham to marketing and there is huge spam volume from AWS too).
If you run a mail server it's good to have a local DNS cache, e. g. Unbound. And if you have Unbound adding an upstream is not that necessary - it can talk to root servers directly or use hoster's DNS as upstream. I rarely use services like Quad9 but IMHO the main use case is for home PC / notebooks: e. g. if an ISP neglected it's own DNS (and it doesn't work well) or if an ISP spoof NXDOMAIN to return ads; another use case is free Wi-Fi where DNS can also be misconfigured / unreliable.
For an ISP it's relatively easy to provide a DNS server which will be fast and reliable (and your ISP's DNS is close to you than some 3rd party DNS) if that's not the case they probably just don't care.
Traceroute works by observing Internet Control Message Protocol (ICMP) time to live/hop count exceeded messages and noting the source IP of those messages. There's plenty of resources you can search on to learn more about this. When you see * * *, it means that for that given TTL value, no corresponding ICMP messages were returned to the source.
It could be because they were filtered at the boundary of the network. If source IPs are private (RFC-1918 or carrier grade NAT space), those ICMP messages should get dropped. This is Best Current Practice (BCP) 38, if you wanted to read more about it.
Ever want to know why IPv6 is so important? This is another reason why. Troubleshooting networks without globally significant IP addresses on the intermediate hops is a real pain.
It's a really nice voltage with lots of support for batteries and up/dn conversion hardware.
It's also right at the edge of what is human safe. You can burn yourself and blow up cables, but it's very difficult to electrocute yourself (afib or muscle seize) without lots of wet contact.
Indeed, I'm aware of only one recorded death by electrocution at 48V, iirc it was a Swiss radio amateur that had done a bunch of gardening sat down sweaty in a metallic chair and reached for the one switch of his set. Probably there were other contributory causes as well, I've been zapped multiple times from much higher voltage sources (that could have easily supplied the power required) and lived.
I can't find a reference for that Swiss case though. I'll keep looking.
It is with respect to ground, the positive pole of the battery is connected to ground.
The telegraph system figured this out very quickly. Most water in nature has at least a bit of salt in it, which is present as positive sodium ions and negative chloride ions. By making the outdoor wiring negative with respect to ground, the chloride ions are repelled, and such wires corrode much more slowly than those that're positive with respect to ground.
Since most of the telegraph network, later the telephone network, is outdoors, this is a pretty big deal.
You tie one of the leads to earth (literally grounding it)[1], leaving the other non-grounded. Depending on if you tie the negative or the positive lead to ground, you get 48V or -48V with respect to ground. As long as the potential between the most positive lead and the least positive lead is 48V, the circuit itself doesn't care.
As mentioned here[2], the reason for grounding the positive lead is to prevent galvanic corrosion[3] destroying the buried copper.
Generally with respect to ground. There are many good reasons to connect your power system to ground and so this is commonly done. (there are pros and cons to connecting to ground, but it gets complex fast)
No. In telco, the -48V is referenced against ground, like the physical ground. If you're isolated, you can do this. but they would still need to be referencing the 'ground' to something ... likely the negative side of the main battery pack.
The reason why -48V is used is because it is provided as a bias voltage to give wiring cathodic protection, to prevent corrosion of telecom infrastructure. If you used 48V, it would not work. You need a negative voltage referenced against ground.
It works, but anytime you have custom networking or more complex cloud-init configs, you'll have to go into "snippets" territory or referring to files in a local filesystem of the host. They don't have API support for making snippets the last time I checked. Where I ran into this was when trying to set up hosts with Terraform on Proxmox VE (which works well itself too).
The best way to handle this (which is really terrible, honestly, but it works) is to make configdrive2 ISOs locally, and upload those using the API. That is, don't give Proxmox a cloud-init snippet, but rather a fully-built cloud-init ISO. This is basically bypassing/reimplementing Proxmox's cloud-init features yourself, which is terrible. But it works really well.
I agree. It absolutely is IPv4. Hosts could use DHCPv6 with prefix delegation (DHCPv6-PD), and use that delegated /64 for its internal Docker bridge and get rid of NAT. And yes, you can still have your Netfilters stateful packet filtering in place! People are going through so much pain because they won't embrace the tools IPv6 gives you! This solution is 20 years old. God help you if your network is actually using 172.17.0.0/16. grumble grumble get off my lawn, kids.
The first movement is one of the only pieces I can play on the piano. Yes indeed, anyone can learn it! I came from a musical family, but never really put the effort into learning the piano.
I'm not sure where I heard this, but Beethoven wrote this for one of his students that he was in love with. The first movement was purposefully written for a newcomer to be able to play--such as for whom he admired, but the third movement was a representation of his anger over being rejected, and is one of the hardest piano pieces to play.
If one wants to play a well-known sonata I'd rather start with the Tempest. Considerably easier than Moonlights 3rd. And as beautiful imho, the 3rd movement especially.
Cisco's SiliconOne is programmable using P4 as well. I'd be curious to know if it'd work for your use cases. It certainly isn't going anywhere since we're using it in darn near all our products now.
https://github.com/jauderho/nts-servers/tree/main