Information AboutDnsbl |
| CATEGORIES ABOUT DNSBL | |
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DNSBL names a medium, not any specific list or policy. There has been a good deal of controversy over the past several years over the operation of specific lists, such as the MAPS RBL and SPEWS . TERMINOLOGY The following are all closely related terms:
HISTORY OF DNSBLS The first DNSBL was the Real-time Blackhole List (RBL), created in 1997 by Paul Vixie and Dave Rand as part of the Mail Abuse Prevention System (MAPS) . Initially, the RBL was not a DNSBL, but rather a list of commands that could be used to program Router s so that network operators could Blackhole all TCP/IP traffic for machines used to send spam or host spam supporting services, such as a website. Vixie, an influential Internet programmer, network administrator and CTO of AboveNet , was able to install these blackhole routes in key routers so that many people across the internet would not be able to connect to these machines, even if they wanted to. The purpose of the RBL was not simply to block spam—it was to educate Internet Service Provider s and other Internet sites about spam and related problems, such as open SMTP relays, Spamvertising , etc. Before an address would be listed on the RBL, volunteers and MAPS staff would attempt repeatedly to contact the persons responsible for it and get its problems corrected. Such effort was considered very important before blackholing all network traffic, but it also meant that spammers and spam supporting ISPs could delay being put on the RBL for long periods while such discussions went on. Later, the RBL was also released in a DNSBL form and Paul Vixie encouraged the authors of Sendmail and other mail software to implement RBL clients. These allowed the mail software to query the RBL and reject mail from listed sites on a per mail server basis instead of blackholing all traffic. Soon after the advent of the RBL, others started developing their own lists with different policies. One of the first was Alan Brown's Open Relay Behavior-modification System (ORBS) . This used automated testing to discover and list mail servers running as Open Mail Relay s—exploitable by Spammers to carry their spam. ORBS was controversial at the time because many people felt running an open relay was acceptable, and that scanning the Internet for open mail servers could be abusive. In 2003 , a number of DNSBLs have come under Denial-of-service Attack s. Since no party has admitted to these attacks nor been discovered responsible, their purpose is a matter of speculation. However, many observers believe the attacks are perpetrated by spammers in order to interfere with the DNSBLs' operation or hound them into shutting down. In August 2003 , the firm '' Osirusoft '', an operator of several DNSBLs including one based on the SPEWS data set, shut down its lists after suffering weeks of near-continuous attack. ''Major events: ORBS Controversy , lawsuits, RBL Commercialization , ORBS Breakup , ORBZ , SBL , SPEWS , RHSBLs '' DNSBL OPERATION To operate a DNSBL requires three things: a domain to host it under, a nameserver for that domain, and a list of addresses to publish. It is possible to serve a DNSBL using 's rbldns —is faster, uses less memory, and is easier to configure than the general-purpose BIND. Alternatively, Simplicita Software offers a commercial DNSBL server that provides additional benefits such as point-in-time auditing and 24/7 IP address monitoring. The hard part of operating a DNSBL is populating it with addresses. DNSBLs intended for public use usually have specific, published policies as to what a listing means, and must be operated accordingly to attain or keep public confidence. DNSBL queries When a mail server receives a connection from a client, and wishes to check that client against a DNSBL (let's say, ''dnsbl.example.net''), it does more or less the following: #Take the client's IP address—say, ''192.168.42.23''—and reverse the bytes, yielding ''23.42.168.192''. #Append the DNSBL's domain name: ''23.42.168.192.dnsbl.example.net''. #Look up this name in the DNS as a domain name ("A" record). This will return either an address, indicating that the client is listed; or an "NXDOMAIN" ("No such domain") code, indicating that the client is not. #Optionally, if the client is listed, look up the name as a text record ("TXT" record). Most DNSBLs publish information about why a client is listed as TXT records. Looking up an address in a DNSBL is thus similar to looking it up in reverse-DNS. The differences are that a DNSBL lookup uses the "A" rather than "PTR" record type, and uses a forward domain (such as ''dnsbl.example.net'' above) rather than the special reverse domain ''in-addr.arpa''. There is an informal protocol for the addresses returned by DNSBL queries which match. Most DNSBLs return an address in the 127.0.0.0/8 IP Loopback network. The address 127.0.0.2 indicates a generic listing. Other addresses in this block may indicate something specific about the listing—that it indicates an open relay, proxy, spammer-owned host, etc. {Link without Title} DNSBL policies Different DNSBLs have different policies. DNSBL policies differ from one another on three fronts:
CRITICISMS Email users who find their messages blocked from mail servers that use DNSBLs often object vociferously, sometimes to the extent of attacking the existence of the lists themselves. The following lists are controversial:
Although many have voiced objections to specific DNSBLs, few people object to the principle that mail-receiving sites should be able to reject undesired mail systematically. One who does is John Gilmore , who deliberately operates an Open Mail Relay . Gilmore accuses DNSBL operators of violating Antitrust law. For Joe Blow to refuse emails is legal (though it's bad policy, akin to "shooting the messenger"). But if Joe and ten million friends all gang up to make a blacklist, they are exercising illegal monopoly power. A number of parties, such as the Electronic Frontier Foundation and Peacefire , have raised concerns about some use of DNSBLs by ISP s. One joint statement issued by a group including EFF and Peacefire addressed " Stealth Blocking ", in which ISPs use DNSBLs or other spam-blocking techniques without informing their clients. {Link without Title} Spammers have pursued lawsuits against DNSBL operators on similar grounds:
SEE ALSO NOTES AND REFERENCES EXTERNAL LINKS
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