Unterschiede
Hier werden die Unterschiede zwischen zwei Versionen angezeigt.
Vorhergehende Überarbeitung | |||
— | centos:mail_c7:spam_1 [22.07.2019 15:01. ] (aktuell) – Externe Bearbeitung 127.0.0.1 | ||
---|---|---|---|
Zeile 1: | Zeile 1: | ||
+ | ====== SPAM-Abwehr mit Hilfe von Greylisting ====== | ||
+ | {{: | ||
+ | |||
+ | Beides, **// | ||
+ | |||
+ | Für den ersten groben SPAM-Schutz setzen wir auf **greylisting**-Mechanismen. Greylisting macht es sich zu eigen, das unterschiedliche Verhalten von SPAMern und richtigen Mailservern zu betrachten. Beim greylisting werden folgende vier Schritte durchlaufen bzw. bewertet: | ||
+ | - Der MTA bewertet die drei folgenden technischen Eckdaten eines Zustellversuches, | ||
+ | * **Absender-IP-Adresse** | ||
+ | * **eMail-Adresse des Absenders** | ||
+ | * **eMail-Adresse des Empfängers** | ||
+ | - Das Tripple aus IP-Adresse, Sender- und Empfänger-eMail-Adresse speichert der MTA nun in einer separaten Berkley-DB ab. Ist dieses Tripple neu, d.h. es wurde noch keine eMail von dem Absender an unseren Empfänger von diesem Mailserver eingeliefert, | ||
+ | - Ist der einliefernde Host ein SPAMer wird er die Nachricht verwerfen und sein Glück bei anderen weniger geschützten MTTAs versuchen. Ein richtiger Mailserver wird seine eMail in die deferred-Queue einstellen und nach wenigen Minuten einen erneuten Zustellversuch unternehmen. | ||
+ | - Kommt der einliefernde Mailserver erneut, wird nun das Tripple aus IP-Adresse, Sender- und Empfänger-eMail-Adresse positiv bewertet und unser MTA wird mit der weiteren Prüfung und Bewertung der eMail fortfahren. | ||
+ | |||
+ | ===== Installation ===== | ||
+ | Für das Thema greylisting greifen wir auf das Paket **postgrey** von [[http:// | ||
+ | |||
+ | Wir installieren also zu erst einmal das betreffende Paket mit Hilfe von **YUM**. | ||
+ | # yum install postgrey -y | ||
+ | |||
+ | Was uns das RPM alles auf unseren Server gebracht hat, finden wir mit Hilfe des Befehls **rpm** heraus. | ||
+ | # rpm -qil postgrey | ||
+ | |||
+ | < | ||
+ | Version | ||
+ | Release | ||
+ | Architecture: | ||
+ | Install Date: Wed 05 Nov 2014 12:52:11 PM CET | ||
+ | Group : Unspecified | ||
+ | Size : 106568 | ||
+ | License | ||
+ | Signature | ||
+ | Source RPM : postgrey-1.34-12.el7.src.rpm | ||
+ | Build Date : Fri 07 Feb 2014 01:44:13 AM CET | ||
+ | Build Host : buildvm-03.phx2.fedoraproject.org | ||
+ | Relocations : (not relocatable) | ||
+ | Packager | ||
+ | Vendor | ||
+ | URL : http:// | ||
+ | Summary | ||
+ | Description : | ||
+ | Postgrey is a Postfix policy server implementing greylisting. When a request | ||
+ | for delivery of a mail is received by Postfix via SMTP, the triplet CLIENT_IP / | ||
+ | SENDER / RECIPIENT is built. If it is the first time that this triplet is | ||
+ | seen, or if the triplet was first seen less than 5 minutes, then the mail gets | ||
+ | rejected with a temporary error. Hopefully spammers or viruses will not try | ||
+ | again later, as it is however required per RFC. | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | / | ||
+ | </ | ||
+ | |||
+ | ===== Konfiguration ===== | ||
+ | Genau genommen müssen wir eigentlich nicht **postgrey** sondern **postfix** konfigurieren. | ||
+ | |||
+ | Bei der [[centos: | ||
+ | # vim / | ||
+ | <code bash>... | ||
+ | |||
+ | ################################################################################ | ||
+ | ## SMTP RECIPIENT RESTRICTIONS | ||
+ | # | ||
+ | # Django : 2014-10-29 - Schutz unserer Empfänger mit Hilfe der Recipient | ||
+ | # Restrictions | ||
+ | # default: smtpd_recipient_restrictions = | ||
+ | smtpd_recipient_restrictions = | ||
+ | # Postmaster, abuse und andere aufgaben- oder funktionsgebundene | ||
+ | # eMail-Adressen (Role-Accounts) whitelisten | ||
+ | | ||
+ | |||
+ | # Black- und Whitelisting | ||
+ | | ||
+ | | ||
+ | | ||
+ | | ||
+ | |||
+ | # Unsere eigenen Nutzer zulassen-/ | ||
+ | # (Kapitel 8.2.2 Relaying erlauben und verbieten) | ||
+ | | ||
+ | | ||
+ | |||
+ | # RBL überprüfen | ||
+ | | ||
+ | | ||
+ | | ||
+ | | ||
+ | |||
+ | # Greylisting via postgrey checken via Unix-Socket | ||
+ | # (Kapitel 9.2.5 postgrey installieren) | ||
+ | | ||
+ | |||
+ | # Policyd-Weight check over TCP-Connection | ||
+ | # (Kapitel 9.3 policyd-weight installieren) | ||
+ | # check_client_access btree:/ | ||
+ | # check_policy_service inet: | ||
+ | |||
+ | # Dynamische Prüfung auf existente Relay-Empfänger | ||
+ | # (Kapitel 12.2.2 Dynamische Empfänger-Verifizierung) | ||
+ | | ||
+ | |||
+ | # Backupserver (MX) erlauben | ||
+ | | ||
+ | |||
+ | # alles andere an relaying verbieten | ||
+ | # (Kapitel 8.2.2 Relaying erlauben und verbieten) | ||
+ | | ||
+ | |||
+ | # Quota-Status-Policy-Daemon am Dovecot-Backend-System | ||
+ | # Dovecotbuch (ISBN 978-3-95539-74-7) Seite 219 ff. | ||
+ | # (Kapitel 11.11 "Der Quota-Policy-Server für Postfix" | ||
+ | | ||
+ | |||
+ | # Zu guter Letzt alles durchlassen, | ||
+ | # beanstandet wurde | ||
+ | | ||
+ | </ | ||
+ | |||
+ | ===== postgrey starten ===== | ||
+ | Beim vorliegenden postgrey-RPM ist neben der Festlegung von User- und Dateirechten auch gleich ein passendes Startupscript installiert worden. Somit reicht ein einfaches **service postgrey start** aus: | ||
+ | # systemctl start postgrey | ||
+ | |||
+ | Fragen wir nun den Status des Daemon ab erhalten wir den genauen Status angezeigt. | ||
+ | # systemctl status postgrey | ||
+ | |||
+ | < | ||
+ | | ||
+ | | ||
+ | Docs: man: | ||
+ | Process: 6074 ExecStart=/ | ||
+ | Process: 6072 ExecStartPre=/ | ||
+ | Main PID: 6076 (/ | ||
+ | | ||
+ | | ||
+ | |||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org systemd[1]: PID file / | ||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org postgrey[6076]: | ||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org postgrey[6076]: | ||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org postgrey[6076]: | ||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org postgrey[6076]: | ||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org postgrey[6076]: | ||
+ | Nov 05 13:09:04 vml000087.dmz.nausch.org systemd[1]: Started Postfix Greylisting Service. | ||
+ | </ | ||
+ | |||
+ | Auch im Maillog finden wir diese Zeilen wieder. | ||
+ | # less / | ||
+ | |||
+ | < | ||
+ | Nov 5 13:09:04 vml000087 postgrey[6076]: | ||
+ | Nov 5 13:09:04 vml000087 postgrey[6076]: | ||
+ | Nov 5 13:09:04 vml000087 postgrey[6076]: | ||
+ | Nov 5 13:09:04 vml000087 postgrey[6076]: | ||
+ | </ | ||
+ | |||
+ | |||
+ | Mit einem Blick in die Prozessliste können wir uns vergewissern, | ||
+ | # ps auxw | grep postgrey | ||
+ | |||
+ | | ||
+ | |||
+ | Damit nun unser Diesnt beim Starten automatisch starten, sorgen wir mit folgendem Aufruf. | ||
+ | # systemctl enable postgrey | ||
+ | |||
+ | ln -s '/ | ||
+ | |||
+ | Wollen wir überprüfen ob der Dienst automatisch startet, verwenden wir folgenden Aufruf. | ||
+ | # systemctl is-enabled postgrey | ||
+ | |||
+ | | ||
+ | |||
+ | Die Rückmeldung **enabled** zeigt an, dass der Dienst automatisch startet; ein **disabled** zeigt entsprechend an, dass der Dienst __nicht__ automatisch startet. | ||
+ | |||
+ | ===== postgrey Administration ===== | ||
+ | Die Konfigurationsdateien rund um postgrey befinden sich im Verzeichnis // | ||
+ | # ll / | ||
+ | < | ||
+ | -rw-r--r--. 1 root root 59 Feb 7 2014 / | ||
+ | -rw-r--r--. 1 root root 188 May 4 2011 / | ||
+ | </ | ||
+ | |||
+ | Die Konfigurationsdateien im Verzeichnis / | ||
+ | |||
+ | * **postgrey_whitelist_clients** Tabelle zur Definition von Ausnahmeregeln beim Greylisting-Daemon, | ||
+ | # -------------------------------------------- | ||
+ | # put this file in / | ||
+ | # with --whitelist-clients=xxx | ||
+ | # | ||
+ | # postgrey version: 1.34, build date: 2011-05-04 | ||
+ | |||
+ | # greylisting.org: | ||
+ | southwest.com | ||
+ | # greylisting.org: | ||
+ | isp.belgacom.be | ||
+ | # greylisting.org: | ||
+ | ameritradeinfo.com | ||
+ | # greylisting.org: | ||
+ | amazon.com | ||
+ | # 2004-05-20: Linux kernel mailing-list (unique sender with letters) | ||
+ | vger.kernel.org | ||
+ | # 2004-06-02: karger.ch, no retry | ||
+ | karger.ch | ||
+ | # 2004-06-02: lilys.ch, (slow: 4 hours) | ||
+ | server-x001.hostpoint.ch | ||
+ | # 2004-06-09: roche.com (no retry) | ||
+ | gw.bas.roche.com | ||
+ | # 2004-06-09: newsletter (no retry) | ||
+ | mail.hhlaw.com | ||
+ | # 2004-06-09: no retry (reported by Ralph Hildebrandt) | ||
+ | prd051.appliedbiosystems.com | ||
+ | # 2004-06-17: swissre.com (no retry) | ||
+ | swissre.com | ||
+ | # 2004-06-17: dowjones.com newsletter (unique sender with letters) | ||
+ | returns.dowjones.com | ||
+ | # 2004-06-18: switch.ch (works but personnel is confused by the error) | ||
+ | domin.switch.ch | ||
+ | # 2004-06-23: accor-hotels.com (slow: 6 hours) | ||
+ | accor-hotels.com | ||
+ | # 2004-06-29: rr.com (no retry, reported by Duncan Hill) | ||
+ | / | ||
+ | # 2004-06-29: cox.net (no retry, reported by Duncan Hill) | ||
+ | / | ||
+ | # 2004-06-29: motorola.com (no retry) | ||
+ | mot.com | ||
+ | # 2004-07-01: nic.fr (address verification, | ||
+ | nic.fr | ||
+ | # 2004-07-01: verizon.net (address verification, | ||
+ | / | ||
+ | # 2004-07-02: cs.columbia.edu (no retry) | ||
+ | cs.columbia.edu | ||
+ | # 2004-07-02: papersinvited.com (no retry) | ||
+ | 66.216.126.174 | ||
+ | # 2004-07-02: telekom.de (slow: 6 hours) | ||
+ | / | ||
+ | # 2004-07-04: tiscali.dk (slow: 12 hours, reported by Klaus Alexander Seistrup) | ||
+ | / | ||
+ | # 2004-07-04: freshmeat.net (address verification) | ||
+ | freshmeat.net | ||
+ | # 2004-07-11: zd-swx.com (unique sender with letters, reported by Bill Landry) | ||
+ | zd-swx.com | ||
+ | # 2004-07-11: lockergnome.wc09.net (unique sender with letters, reported by Bill Landry) | ||
+ | lockergnome.wc09.net | ||
+ | # 2004-07-19: mxlogic.net (no retry, reported by Eric) | ||
+ | p01m168.mxlogic.net | ||
+ | p02m169.mxlogic.net | ||
+ | # 2004-09-08: intel.com (pool on different subnets) | ||
+ | / | ||
+ | # 2004-09-17: cox-internet.com (no retry, reported by Rod Roark) | ||
+ | / | ||
+ | # 2004-10-11: logismata.ch (no retry) | ||
+ | logismata.ch | ||
+ | # 2004-11-25: brief.cw.reum.de (no retry, reported by Manuel Oetiker) | ||
+ | brief.cw.reum.de | ||
+ | # 2004-12-03: ingeno.ch (no retry) | ||
+ | qmail.ingeno.ch | ||
+ | # 2004-12-06: rein.ch (no retry) | ||
+ | mail1.thurweb.ch | ||
+ | # 2005-01-26: tu-ilmenau.de (no retry) | ||
+ | piggy.rz.tu-ilmenau.de | ||
+ | # 2005-04-06: polymed.ch (no retry) | ||
+ | mail.polymed.ch | ||
+ | # 2005-06-08: hu-berlin.de (slow: 6 hours, reported by Joachim Schoenberg) | ||
+ | rz.hu-berlin.de | ||
+ | # 2005-06-17: gmail.com (big pool, reported by Beat Mueller) | ||
+ | proxy.gmail.com | ||
+ | # 2005-06-23: cacert.org (address verification, | ||
+ | cacert.org | ||
+ | # 2005-07-27: polytech.univ-mrs.fr (no retry, reported by Giovanni Mandorino) | ||
+ | polytech.univ-mrs.fr | ||
+ | # 2005-08-05: gnu.org (address verification, | ||
+ | gnu.org | ||
+ | # 2005-08-17: ciphirelabs.com (needs fast responses, reported by Sven Mueller) | ||
+ | cs.ciphire.net | ||
+ | # 2005-11-11: lufthansa (no retry, reported by Peter Bieringer) | ||
+ | / | ||
+ | # 2005-11-23: arcor-online.net (slow: 12 hours, reported by Bernd Zeimetz) | ||
+ | / | ||
+ | # 2005-12-29: netsolmail.com (no retry, reported by Gareth Greenaway) | ||
+ | netsolmail.com | ||
+ | # mail.likopris.si (no retry, reported by Vito Robar) | ||
+ | 193.77.153.67 | ||
+ | # jcsw.nato.int (several servers, no retry, reported by Vito Robar) | ||
+ | 195.235.39 | ||
+ | # tesla.vtszg.hr (no retry, reported by Vito Robar) | ||
+ | tesla.vtszg.hr | ||
+ | # mailgw*.iai.co.il (pool of several servers, reported by Vito Robar) | ||
+ | / | ||
+ | # gw.stud-serv-mb.si (no retry, reported by Vito Robar) | ||
+ | gw.stud-serv-mb.si | ||
+ | # mail.commandtech.com (no retry, reported by Vito Robar) | ||
+ | 216.238.112.99 | ||
+ | # duropack.co.at (no retry, reported by Vito Robar) | ||
+ | 193.81.20.195 | ||
+ | # mail.esimit-tech.si (no retry, reported by Vito Robar) | ||
+ | 193.77.126.208 | ||
+ | # mail.resotel.be (ocasionally no retry, reported by Vito Robar) | ||
+ | 80.200.249.216 | ||
+ | # mail2.alliancefr.be (ocasionally no retry, reported by Vito Robar) | ||
+ | mail2.alliancefr.be | ||
+ | # webserver.turboinstitut.si (no retry, reported by Vito Robar) | ||
+ | webserver.turboinstitut.si | ||
+ | # mil.be (pool of different servers, reported by Vito Robar) | ||
+ | 193.191.218.141 | ||
+ | 193.191.218.142 | ||
+ | 193.191.218.143 | ||
+ | 194.7.234.141 | ||
+ | 194.7.234.142 | ||
+ | 194.7.234.143 | ||
+ | # mail*.usafisnews.org (no retry, reported by Vito Robar) | ||
+ | / | ||
+ | # odk.fdv.uni-lj.si (no retry, reported by Vito Robar) | ||
+ | / | ||
+ | # rak-gentoo-1.nameserver.de (no retry, reported by Vito Robar) | ||
+ | rak-gentoo-1.nameserver.de | ||
+ | # dars.si (ocasionally no retry, reported by Vito Robar) | ||
+ | mx.dars.si | ||
+ | # cosis.si (no retry, reported by Vito Robar) | ||
+ | 213.143.66.210 | ||
+ | # mta? | ||
+ | / | ||
+ | # pim-N-N.quickinspirationsmail.com (unique sender, reported by Vito Robar) | ||
+ | / | ||
+ | # flymonarch (no retry, reported by Marko Djukic) | ||
+ | flymonarch.com | ||
+ | # wxs.nl (no retry, reported by Johannes Fehr) | ||
+ | / | ||
+ | # ibm.com (big pool, reported by Casey Peel) | ||
+ | ibm.com | ||
+ | # messagelabs.com (big pool, reported by John Tobin) | ||
+ | / | ||
+ | # ptb.de (slow, reported by Joachim Schoenberg) | ||
+ | berlin.ptb.de | ||
+ | # registrarmail.net (unique sender names, reported by Simon Waters) | ||
+ | registrarmail.net | ||
+ | # google.com (big pool, reported by Matthias Dyer, Martin Toft) | ||
+ | google.com | ||
+ | # orange.fr (big pool, reported by Lo�c Le Loarer) | ||
+ | / | ||
+ | # citigroup.com (slow retry, reported by Michael Monnerie) | ||
+ | / | ||
+ | # cruisingclub.ch (no retry) | ||
+ | mail.ccs-cruising.ch | ||
+ | # digg.com (no retry, Debian #406774) | ||
+ | diggstage01.digg.com | ||
+ | # liberal.ca (retries only during 270 seconds, Debian #406774) | ||
+ | smtp.liberal.ca | ||
+ | # pi.ws (pool + long retry, Debian #409851) | ||
+ | / | ||
+ | # rambler.ru (big pool, reported by Michael Monnerie) | ||
+ | rambler.ru | ||
+ | # free.fr (big pool, reported by Denis Sacchet) | ||
+ | / | ||
+ | / | ||
+ | # thehartford.com (pool + long retry, reported by Jacob Leifman) | ||
+ | / | ||
+ | # abb.com (only one retry, reported by Roman Plessl) | ||
+ | / | ||
+ | # 2007-07-27: sourceforge.net (sender verification) | ||
+ | lists.sourceforge.net | ||
+ | # 2007-08-06: polytec.de (no retry, reported by Patrick McLean) | ||
+ | polytec.de | ||
+ | # 2007-09-06: qualiflow.com (no retry, reported by Alex Beckert) | ||
+ | / | ||
+ | # 2007-09-07: nrl.navy.mil (no retry, reported by Axel Beckert) | ||
+ | nrl.navy.mil | ||
+ | # 2007-10-18: aliplast.com (long retry, reported by Johannes Feigl) | ||
+ | mail.aliplast.com | ||
+ | # 2007-10-18: inode.at (long retry, reported by Johannes Feigl) | ||
+ | / | ||
+ | # 2008-02-01: bol.com (no retry, reported by Frank Breedijk) | ||
+ | / | ||
+ | # 2008-06-05: registeredsite.com (no retry, reported by Fred Kilbourn) | ||
+ | / | ||
+ | # 2008-07-17: mahidol.ac.th (no retry, reported by Alex Beckert) | ||
+ | saturn.mahidol.ac.th | ||
+ | # 2008-07-18: ebay.com (big pool, reported by Peter Samuelson) | ||
+ | ebay.com | ||
+ | # 2008-07-22: yahoo.com (big pool, reported by Juan Alonso) | ||
+ | yahoo.com | ||
+ | # 2008-11-07: facebook (no retry, reported by Tim Freeman) | ||
+ | / | ||
+ | # 2009-02-10: server14.cyon.ch (long retry, reported by Alex Beckert) | ||
+ | server14.cyon.ch | ||
+ | # 2009-08-19: 126.com (big pool) | ||
+ | / | ||
+ | # 2010-01-08: tifr.res.in (no retry, reported by Alex Beckert) | ||
+ | home.theory.tifr.res.in | ||
+ | # 2010-01-08: 1blu.de (long retry, reported by Alex Beckert) | ||
+ | ms4-1.1blu.de | ||
+ | # 2010-03-17: chello.at (big pool, reported by Jan-willem van Eys) | ||
+ | / | ||
+ | # 2010-05-31: nic.nu (long retry, reported by Ivan Sie) | ||
+ | mx.nic.nu | ||
+ | # 2010-06-10: Microsoft servers (long/no retry, reported by Roy McMorran) | ||
+ | bigfish.com | ||
+ | frontbridge.com | ||
+ | microsoft.com | ||
+ | # 2010-06-18: Google/ | ||
+ | postini.com | ||
+ | # 2011-02-04: evanzo-server.de (no retry, reported by Andre Hoepner) | ||
+ | / | ||
+ | # 2011-05-02: upcmail.net (big pool, reported by Michael Monnerie) | ||
+ | upcmail.net | ||
+ | </ | ||
+ | * **postgrey_whitelist_clients.local** Tabelle zur Definition von lokalen Ausnahmeregeln beim Greylisting-Daemon. Bei Bedarf wird man hier in dieser Tabelle individuelle Definitionen vornehmen. < | ||
+ | # 2008-10-08: 1und1.com (big pool, inserted by Django) | ||
+ | # | ||
+ | / | ||
+ | </ | ||
+ | * **postgrey_whitelist_recipients** Tabelle zur Definition von Ausnahmeregeln beim Greylisting-Daemon, | ||
+ | # -------------------------------------- | ||
+ | # put this file in / | ||
+ | # with --whitelist-recipients=xxx | ||
+ | |||
+ | postmaster@ | ||
+ | abuse@ | ||
+ | </ | ||
+ | |||
+ | <WRAP round important> | ||
+ | Nach Änderungen an den Postgrey Ausnahmelisten **postgrey_whitelist_clients.local** und **postgrey_whitelist_recipients** ist der Daemon von den Änderungen mit einem reload in Kenntnis zu setzen! | ||
+ | # systemctl restart postgrey | ||
+ | </ | ||
+ | |||
+ | ===== erfolgreiches Greylisting | ||
+ | Am nachfolgenden Beispiel sehen wir, dass ein Connectversuch von einem uns unbekanntem Mailserver erst einmal mit einem **450er** abgewiesen wird und später nocheinmal zugestellt werden soll. | ||
+ | < | ||
+ | Oct 12 04:35:41 nss postgrey[8228]: | ||
+ | Oct 12 04:35:41 nss postgrey[8228]: | ||
+ | Oct 12 04:35:41 nss postfix/ | ||
+ | Oct 12 04:35:41 nss postfix/ | ||
+ | Beim nächsten Zustellversuch wird die eMail dann entsprechend akzeptiert: | ||
+ | < | ||
+ | Oct 12 11:28:41 nss postgrey[8228]: | ||
+ | Oct 12 11:28:41 nss postfix/ | ||
+ | Oct 12 11:28:41 nss postfix/ | ||
+ | Oct 12 11:28:41 nss postfix/ | ||
+ | Oct 12 11:28:41 nss postfix/ | ||
+ | Oct 12 11:28:41 nss postfix/ | ||
+ | Oct 12 11:31:13 nss postfix/ | ||
+ | |||
+ | ===== graphische Statistiken Greylisting | ||
+ | Will man sich einen generellen Überblick über die Greylisting-Auswirkungen beim Mailverkehr informieren, | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | ===== FAZIT ===== | ||
+ | |||
+ | Postgrey hat sich in der Abwehr von SPAM und anderen unerwünschten Verkehrs bestens bewährt, kann so doch jede Menge des unerwünschten Traffics abgelehnt werden. | ||
+ | |||
+ | Da es aber bei der initilaen Kontaktaufnahme immer zu ca. 5 Minuten Verzögerung oder auch mehr kommt, sind viele Anwender unglücklich, | ||
+ | |||
+ | Mittlerweilen erzielt man mit entsprechend konfigurierten **[[centos: | ||
+ | |||
+ | <WRAP center round tip> | ||
+ | **summa sumarum:** | ||
+ | |||
+ | In Zeiten von immer stärkeren Echtzeitkommunikationswünschen seiten der Anwender/ | ||
+ | |||
+ | </ | ||
+ | |||
+ | ====== Links ====== | ||
+ | * **⇐ [[centos: | ||
+ | * **⇒ [[centos: | ||
+ | * **[[centos: | ||
+ | * **[[wiki: | ||
+ | * **[[http:// | ||
+ | |||