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78

ping -a w.x.y.z Should resolve the name from the IP address if the reverse lookup zone has been set up properly. If the reverse lookup zone does not have an entry for the record, the -a will just ping without a name.


32

nslookup <ip> Does what you're looking for. It will tell you the server you're querying and the result. For example: c:\>nslookup 192.168.101.39 Server: dns1.local Address: 192.168.101.24 Name: enigma.local Address: 192.168.101.39


30

The trouble with "ping" is that it's not strictly a name server lookup tool (like nslookup) - for instance if you ping a hostname, it can be resolved to an IP address by a number of methods: DNS lookup, host file lookup, WINS (god forbid) or NetBIOS broadcast. It can also return a potentially out-dated cached result. The order in which the methods are ...


26

Short Answer Do the standards governing DNS operation require that all devices have a matching PTR record? No. Do the standards for certain protocols require PTR records that agree with corresponding A or AAAA records? Yes. Do some applications not governed by a RFC have the same requirements? Yes. Is mandatory PTR record creation a best practice? ...


23

Delegating a /22 is easy, it's delegation of the 4 /24s. A /14 is delegation of the 4 /16s, etc. RFC2317 covers the special cases with a netmask longer than /24. Basically there's no super-clean way to do delegation of in-addr.arpa zones on anything but octet boundaries, but you can work around this. Let's say I want to delegate 172.16.23.16/29, which ...


22

From RFC 4408: 3.1.2. Multiple DNS Records A domain name MUST NOT have multiple records that would cause an authorization check to select more than one record. See Section 4.5 for the selection rules. I'm not entirely sure what you want to achieve by adding a second record, but if it is something like adding extra hosts/networks as ...


16

What you've got is "forward confirmed reverse DNS"-- that is, the named returned by reverse-lookup, when run thru a forward lookup, returns the same IP as the original IP used in the reverse lookup (see http://en.wikipedia.org/wiki/Forward_Confirmed_reverse_DNS for the more verbose description). That's a good first step. The rejection messages are your best ...


14

Reverse DNS is a mapping from an IP address to a DNS name. So it's like DNS, but backwards. If you are assigned IP addresses you have to setup reverse DNS to tell the world what the addresses are used for. In practice, if you want to know what system is at 216.239.32.10 you design what is called a reverse lookup by reverting the ip address and adding ...


13

dig and host should be what you're looking for ;) http://www.unix.com/unix-dummies-questions-answers/9866-nslookup-linux.html EDIT : nslookup work too finally, I had a blank on that one and tought it wasn't available so I deleted my post lol :P More infos on nslookup command whether it seems to have been replace since a while now : ...


13

on *nix you can use dig -x [address]


13

I'd try as hard as possible to have the reverse lookup for my email server's IP address resolve to the name it's using in SMTP conversations. It makes life easier. I don't have any statistical evidence to back this up, but it has been my experience that, from time to time, messages will be rejected by some remote mailers for not having a reverse lookup that ...


12

Generally what they care about is that the rDNS result resolves back to the original IP. So a typical setup would look like this: www.example.com and www.yourdomain.example both resolve to 192.0.2.1. The PTR for 192.0.2.1 is myhost1.yourdomain.example. myhost1.yourdomain.example resolves to 192.0.2.1. I believe most spam filters consider that to be an ...


12

Probably you're lagging on an attempt to retrieve and verify reverse DNS of the connecting host. You can test this by turning on skip_name_resolve in the server's my.cnf, [mysqld] section. If it is in fact the case (demonstrated by that parameter eliminating the delay), then you can solve the problem by either setting up DNS properly (forward and reverse) ...


11

The DNS system has many kinds of records. "A" records map names to IP addresses. "PTR" records map IP addresses to names. The mapping is not always transitive, and there can be multiple A records that map the the same IP address. Strictly speaking, PTR records map special names to other names. The IP address 194.98.81.144 first must be translated to ...


10

It's extremely common to block SMTP servers that don't have these basics: Hostname in HELO forward resolves to IP connection originated from. Connections origin IP reverses to the Hostname claimed in HELO. If SPF, DKIM, or DMARC policies exist, verify. Anyone griping about getting blocked because of one of these should be tarred and feathered. People who ...


10

It's an RFC violation to use a CNAME as an MX record. From RFC2181 section 10.3: The domain name used as [...] part of the value of a MX resource record must not be an alias. [...] It can also have other RRs, but never a CNAME RR. In practice it will often work, but some MTAs are aware that you shouldn't do it, so assume they can ignore you or ...


9

No. It's not the way DNS works. You can register any number of domains against a single IP, and not bother putting in a reverse DNS entry for any of them if you want. Unless you want to brute force resolve the internet. :)


9

nslookup -type=ptr 10.1.x.x


9

You can do it, but it isn't recommended. There might be cases where you'll break things by setting up multiple records.


9

Just some terminology adjustments here. Reverse DNS isn't setup on your server. Your server is assigned IP addresses and those IP addresses have reverse DNS entries. Those IPs are completely independent of your server. Get the IP address of your server $ ip addr show now check to see if you can resolve it $ host 1.2.3.4 where 1.2.3.4 is your IP e.g. ...


8

Reverse lookup records translate IP addresses back into names. A lot of mail servers like to do this as part of anti-spam measures. You need to request that the party authoritative for the reverse zone your email server lives in create the PTR records. That's probably your ISP. There's nothing you can do in the DNS server in your office-- the rest of the ...


8

nslookup will do reverse DNS on windows just as it can do it on linux. Of course, there isn't a reverse entry for every ip address


8

You don't need to do anything complicated. As soon as your new ISP has told you what your new IP range will be you can request which PTR records should be put on each IP address. Once you've moved, you can tell the old ISP that you no longer require them to maintain PTR records for you. That's it. There's no "harm" in having both sets of IPs having the ...


8

To achieve this you need to create a fake root zone to replace the "root.hints" zone that's normally configured. In named.conf put this: zone "." IN { type master; file "fake.root"; }; and in fake.root put this: $TTL 300 . IN SOA ns. hostmaster.xy.com. ( 20120101 1800 900 604800 86400 ...


8

In order: Six entries caused by Google Chrome checking — twice, apparently — to see if you are the victim of an ISP, or an external advertiser-driven proxy DNS provider, that does NXDOMAIN hijacking. One perfectly ordinary IPv6 address→name lookup for an address in the FD00::/8 block. One perfectly ordinary IPv4 address→name lookup ...


7

I personally prefer the latter, because otherwise you break circular resolution (that is, if you reverse-resolve an IP address to a fully-qualified domain name (FQDN), then forward-resolve the FQDN, you get a different IP address). Circular resolution the other way is unreliable, because many names can resolve to one address; but since an address can only ...


7

To add a PTR record in the GoDaddy DNS Manager, you need to do the following: In the Zone Field Editor go down to the TXT(text) Zone Click Add SPF Record A window will open with 4 tabs (Inbound, Outbound, The well hidden 'PTR' and Outsourced) Go to the PTR tab Check Include PTR and add your public IP


7

It seems the standard Ubuntu 8.04 Apache httpd install comes with a LogFormat that starts with %h and that does a client IP's RDNS lookup. Why oh why?? Replacing it with %a (remote IP address) reduces this problem by ca. 90%. Some remain...


7

Yes, but NOT recommended Most reverse DNS entries only have just one PTR record. While you can have multiple PTR records for the same IP its not recommended unless absolutely needed. A web server with a lot of virtual is one example where I've seen more than one PTR record but I think you'll find this breaks things and causes problems a lot more than it ...


6

The test isn't normally comparing against the SMTP envelope (like you describe as your eyeball-based process), but finding the reverse DNS hostname of the connecting host (if any), running that through forward DNS and seeing if it resolved back to the original IP number. So what you need is 1) to have reverse DNS set up (for the first step) and 2) to have ...



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