Sorbs is a infamous DNS blacklist born to try to fight spam. They have a too much restrictive policy that won’t block spam at all but they just create some pain to your MTA.
They can delist your IP a couple of times but if one of your clients get hacked your good quality MTA will be listed for months, even years!
What they don’t understand is that we work with our IP reputation, so just change the IP is not a valid solution. When a valid MTA got abused to send spam the problem is generally solved in hours, or even minutes. A one month list will generate a great problem to the hacked MTA’s clients.
The only solution is: DON’T USE SORBS AT ALL. The list is not business oriented and so is only valid for lamers, bofh sysadmins and nerds…. ok I’m a bofh, nerd sysadmin but I don’t use Sorbs anymore. Sorry.
NOTA: Tell your sysadmins to NOT USE SORBS.
If your SSH connection is slow, it may depends on your SSH server that is executing reverse DNS lookups to try to identify your details.
Try setting the parameter below to your /etc/ssh/sshd_config and restart your ssh server daemon:
It worked perfectly for me, it may work perfectly with you too.
In this short abstract I’ll show you how did I make my work on trying to create a highly scalable, geo localized and distributed system using the DNS.
What we are going to create is a simple but powerful DNS system that can handle queries for a domain returning records based on the user’s geo location.
To accomplish this task we have to choose a good opensource DNS server. My choice was powerdns (http://wiki.powerdns.com/trac).
Powerdns is a great piece of software. It’s a powerful DNS server daemon that can be configured to fit in different DNS environments.
You can save domain zones into different backends (MySQL, Oracle, bind zone file, ldap, etc), and you can have primary and secondary DNS servers with automatic zone replication. This is all what you need to create a full featured DNS system.
One of the powerdns backends do accomplish the geo lookup task, and it’s called “geobackend” (http://wiki.powerdns.com/trac/browser/trunk/pdns/modules/geobackend/README).
Our test environment will consist in a primary DNS server (powerdns as a master), a secondary DNS server (powerdns as a slave) and a geo lookup DNS server (powerdns as master with geobackend enabled). We will enable automatic zone transfer between the primary and the slave server, so that if you add a new record on the master it will be automatically created on the slave.
So, we need 3 servers with powerdns installed. The installation process may be different in each case, but if you are using debian, the task can be as simple as running by root the following command:
apt-get install pdns-server
Now you need the backend where you will save the zone data. May be you want to choose “MySQL” for the master and “bind format file” for the slave DNS. The geo dns server will not need a zone backend because its single task is to retrieve the caller’s IP address and fetch its geographic location from a particular location file, then lookup this location from a map file and return back to the calling user the associated CNAME record that’s into the map file.
A quick brain guideline is given below.
My system (yourdomain.com) is composed like this:
ns1.yourdomain.com (primary DNS server with mysql backend)
ns2.yourdomain.com (secondary DNS server with auto zone replication on bind zone file)
ns1.geo.yourdomain.com (geo lookup DNS server with geobackend)
I executed the steps below:
On ns1.yourdomain.com you have to:
1) install powerdns with the gmysql backend
2) install MySQL server, create a database and grant a user on that DB
3) configure powerdns as master, with gmysql backend connecting to MySQL
4) please note that this server is authoritative to the “yourdomain.com” zone
5) delegate the “geo” zone with a NS record to the geo dns server: “geo IN NS ns1.geo.yourdomain.com”
6) create the glue record for the geodns with the record: “ns1.geo IN A ip_geo_dns_server”
On ns2.yourdomain.com you have to:
1) install powerdns with the bind backend
2) configure powerdns to be a slave with bind backend and enable ns1.yourdomain.com as a supermaster
3) please note that this server is authoritative to the “yourdomain.com” zone
On ns1.geo.yourdomain.com you have to:
1) install powerdns with the geo backend
2) configure powerdns as master with geobackend
3) please note that this server is authoritative to the “geo.yourdomain.com” zone
4) create a map file to handle the association between your country location (eg: uk) and the CNAME that the server will reply
5) download the location database zone, for example I use: zz.countries.nerd.dk (http://countries.nerd.dk/)
If you need how to do that in details please do not hesitate to write me a email. You will find it into my contact page.
I recently discovered a wonderful DNSBL service reporting you where public Internet IPs are from.
The service is countries.nerd.dk: http://countries.nerd.dk/more.html
You can for example block any mail at your mailserver coming from china or russia, simply integrating this DNSBL with your MTA.
You can even get the country of your IP with dig!
Warning: You need to swap IP octets. If for example the IP to check is 126.96.36.199, you have to call 188.8.131.52.zz.countries.nerd.dk.
root@nbvirtdns1:/# dig TXT 184.108.40.206.zz.countries.nerd.dk
220.127.116.11.zz.countries.nerd.dk. 1047 IN TXT “it”
I would not recommend you to host sites that way, you have to be sure that your ISP give you public IP(s) and setup your router to port forward ports 80, 443, 53, and so on.
There are other problems too:
1) if you want to host more than one site with SSL you must have one public IP for each SSL site or use different SSL ports for each site, because name virtualhosting with SSL is not possible;
2) dsl lines are not designed to be stable. The connection can go down and make your site not visible. This is a major problem if you make the mistake to have your own DNS server on it!! The ISP assigned public IP address can change more than one time a day and you have to sync the DNS zone each time.
3) dsl ips are putted into DNS based blacklists zones. You may not be reached from various HTTP proxy servers around the world. For the same reason you cannot send mails, for example originated from your sites.
4) adsl lines are asymmetric (unbalanced for download). You have few kbytes per second in upload, that is just what you need to publish web sites, so this can be a problem when you have just more than 3 users.
5) you probably have problems with High-Availability and Load-Balancing on domestic hardware and you may have blackouts.
6) DNS subsystem may need primary and secondary DNS servers.
The best way (imho) is to use services like slicehost where you have a HA virtual server slice running linux, public IP addresses, free primary and secondary DNS hosting service, large public bandwidth, disk space… and not last your own root password that you can use to have maintenance on your own server for your own.
Se quello che hai sempre cercato e’ avere il tuo personalissimo server linux up and running 24 ore su 24, SliceHost e’ l’opzione giusta per te.
Questa meravigliosa azienda americana (in Italia purtroppo certe cose ce le sogniamo alla grande!) ha sviluppato un sistema automatico con interfaccia web in grado di fornirti in tempo reale per pochi dollari al mese una tua personalissima macchina virtuale con cui potrai realizzare e gestire il tuo server linux in tutta tranquillita’.
Banda e connettivita’ internazionale a internet non sono un problema e potrai scegliere tra vari tagli di offerte pronte per te.
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Avrai la possibilita’ di scegliere la distribuzione linux che piu’ ti aggrada e il tuo server linux personale sara’ in piedi in pochi secondi.
Noi di TuxWeb lo stiamo utilizzando con successo per gestire i siti internet di alcuni nostri clienti.
Ciao, Dino – http://www.tuxweb.it/