Re: Question for this IP's PTR
f...@dnsbed.com wrote: > Greetings, > > as you see this PTR, > > $ dig -x 1.1.1.1 +short > one.one.one.one. > > so 2.2.2.2 can have the PTR two.two.two.two? and 3.3.3.3 can have > three.three.three.three? A simple counter example is $ dig -x 8.8.8.8 +short dns.google. > Sorry I am not good at the DNS knowledge. Me neither but thanks for the question. It prompted me to visit the one.one.one.one website, which is interesting. I do use 1.1.1.1 for DNS queries in my browser, but this is something much bigger.
Re: Question for this IP's PTR
On Fri, 24 Mar 2023 20:32:31 -0400 Greg Wooledge wrote: > On Sat, Mar 25, 2023 at 08:28:03AM +0800, f...@dnsbed.com wrote: > > Greetings, > > > > as you see this PTR, > > > > $ dig -x 1.1.1.1 +short > > one.one.one.one. > > > > so 2.2.2.2 can have the PTR two.two.two.two? and 3.3.3.3 can have > > three.three.three.three? > > Any IP address can have any PTR value. You just have to petition the > owner of the IP address range to set it. > > I didn't know .one was a valid TLD. It looks like .two is not, so if > someone were to assign "two.two.two.two" as the PTR value of an IP > address, that PTR would not resolve back to any IP address. (An IP > address block owner might reject such a petition.) > In general, at this time, a mail server will look at the IP address of a potential sender, check the PTR, then check for an A record matching the PTR, pointing back to the IP address. The PTR does not (currently) need to be related to an email domain using the address. A competent ISP will have set up its IP addresses with complementary PTR-A record pairs. Unfortunately, many use PTRs in the form x-11-22-33-44 which is perfectly valid, but may be rejected by mail servers as likely spammers (mine does). If you already have a PTR-A pair that doesn't look like this (e.g. is some form of your user name or account reference) you're probably OK. The relevant RFC allows (or did when I last looked) multiple PTR records for one IP address, but I don't think there's much software which can deal with that, or will return more than one. On the other hand, it's quite common for a single mail server to deal with many domains, so it's not reasonable to expect a sender or HELO/EHLO to match the PTR. My email server checks for a complementary PTR-A pair that can both be found in public DNS, and goes no further. I believe that is a typical setting. -- Joe
Re: Question for this IP's PTR
On 2023-03-25 08:32, Greg Wooledge wrote: On Sat, Mar 25, 2023 at 08:28:03AM +0800, f...@dnsbed.com wrote: Greetings, as you see this PTR, $ dig -x 1.1.1.1 +short one.one.one.one. so 2.2.2.2 can have the PTR two.two.two.two? and 3.3.3.3 can have three.three.three.three? Any IP address can have any PTR value. You just have to petition the owner of the IP address range to set it. I didn't know .one was a valid TLD. It looks like .two is not, so if someone were to assign "two.two.two.two" as the PTR value of an IP address, that PTR would not resolve back to any IP address. (An IP address block owner might reject such a petition.) Thanks Greg. I also don't know .one is a valid TLD, looks surprising. But, one.one is owned by a domain registrar (one.com), while one.one.one's zone owner is cloudflare. $ dig one.one soa +short a.b-one-dns.net. hostmaster.one.com. 2013010101 1800 900 1209600 300 $ dig one.one.one soa +short fred.ns.cloudflare.com. dns.cloudflare.com. 2305085481 1 2400 604800 3600 maybe they co-work for this domain. regards.
Re: Question for this IP's PTR
On 25/3/23 08:32, Greg Wooledge wrote: I didn't know .one was a valid TLD. It looks like .two is not, so if someone were to assign "two.two.two.two" as the PTR value of an IP address, that PTR would not resolve back to any IP address. (An IP address block owner might reject such a petition.) There is news of a recent TLD '888' but it's not yet known to whois -- Jeremy (Lists)
Re: Question for this IP's PTR
On Sat, Mar 25, 2023 at 08:28:03AM +0800, f...@dnsbed.com wrote: > Greetings, > > as you see this PTR, > > $ dig -x 1.1.1.1 +short > one.one.one.one. > > so 2.2.2.2 can have the PTR two.two.two.two? and 3.3.3.3 can have > three.three.three.three? Any IP address can have any PTR value. You just have to petition the owner of the IP address range to set it. I didn't know .one was a valid TLD. It looks like .two is not, so if someone were to assign "two.two.two.two" as the PTR value of an IP address, that PTR would not resolve back to any IP address. (An IP address block owner might reject such a petition.)
Question for this IP's PTR
Greetings, as you see this PTR, $ dig -x 1.1.1.1 +short one.one.one.one. so 2.2.2.2 can have the PTR two.two.two.two? and 3.3.3.3 can have three.three.three.three? Sorry I am not good at the DNS knowledge. Regards.
