Обратный DNS каждый раз возвращает другой хост

Итак, я случайно зашел по адресу abc.com и нашел это увлекательным:

$ ping abc.com
PING abc.com (199.181.132.250) 56(84) bytes of data.
64 bytes from m.abc.com (199.181.132.250): icmp_req=1 ttl=237 time=90.3 ms
64 bytes from tdl.disneyuniversity.com (199.181.132.250): icmp_req=2 ttl=237 time=89.8 ms
64 bytes from preschooltime.go.com (199.181.132.250): icmp_req=3 ttl=237 time=95.1 ms
64 bytes from futbolpicante.espnfc.com (199.181.132.250): icmp_req=4 ttl=237 time=98.6 ms
64 bytes from www.worldofcars.go.com (199.181.132.250): icmp_req=5 ttl=237 time=86.9 ms
64 bytes from www.verizon.bravesweepstakes.com (199.181.132.250): icmp_req=6 ttl=237 time=87.9 ms
64 bytes from www.directv.bravesweepstakes.com (199.181.132.250): icmp_req=7 ttl=237 time=87.9 ms
64 bytes from manup.abc.com (199.181.132.250): icmp_req=8 ttl=237 time=88.8 ms
64 bytes from m.onemoredisneyday.com (199.181.132.250): icmp_req=9 ttl=237 time=87.5 ms
64 bytes from finance.abc30.com (199.181.132.250): icmp_req=10 ttl=237 time=87.9 ms
64 bytes from finance.abc13.com (199.181.132.250): icmp_req=11 ttl=237 time=88.0 ms
...

В некотором смысле это похоже на балансировку нагрузки, используемую в прямом DNS, за исключением того, что я не понимаю, как это может быть полезно.

Есть ли какая-то практическая причина для этого или просто следствие того, что все эти сайты размещены за одним и тем же IP-адресом?

ping reverse-dns

Похоже, кто-то просто шутит, или сервер неправильно настроен, или что-то в этом роде. На самом деле обратных записей очень много.

кстати. Я подозреваю, что этот IP-адрес может использоваться для рассылки спама, и эти имена хостов нужны для того, чтобы сбивать с толку фильтры. (но это дикая догадка)

видеть:

$ dig 250.132.181.199.in-addr.arpa -t PTR
;; Truncated, retrying in TCP mode.

; <<>> DiG 9.7.3 <<>> 250.132.181.199.in-addr.arpa -t PTR
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33536
;; flags: qr rd ra; QUERY: 1, ANSWER: 195, AUTHORITY: 4, ADDITIONAL: 2

;; QUESTION SECTION:
;250.132.181.199.in-addr.arpa.  IN      PTR

;; ANSWER SECTION:
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.nightofjoy.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.disneyworld.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.mustdodisney.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.disneytheforce.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.onemoredisneyday.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     s.espnradio.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     fb.steelgetsreal.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     my.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     qa.watchdisneyxd.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     qa.watchabcfamily.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     qa.watchdisneyjunior.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     qa.watchdisneychannel.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     uk.disneycareers.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     abc.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     cdn.musiclounge.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     fdj.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     fdj.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     gma.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hdf.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hub.disneyuniversity.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     itm.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     lnb.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     sam.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     tdl.disneyuniversity.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     ugc.lionking.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     ugc.marypoppins.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     ugv.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     vpd.disneycruise.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     w88.m.fwfest.waltdisneyworld.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.att.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.cox.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.ttdl.disneyuniversity.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.enter.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.charter.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.directv.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.verizon.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.mediacom.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.adventure.bravesweepstakes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneyhome.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.worldofcars.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneycasting.net.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.donovandecker.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneyroommate.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneycampusrep.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneycollateral.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneyinternsinfo.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.missiontimekeeper.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneycastingscout.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneyimaginations.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneyprogramsblog.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.wdwcollegeprogramecard.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.wdwcollegeprogramecard2.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     www.disneyinternationalepresentation.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     1ext.doit.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     25th.disneystore.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     beta.xgames.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     blog.disneyxd.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     bmoc.abc7chicago.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     doit.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     live.dadt.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     live.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     play.toontown.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     prod.waltdisneystudios.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     ugv2.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     blogs.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     cards.babyzone.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     email.doit.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     email.disneymovieclub.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     espn3.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     games.soapnet.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     manup.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     panam.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     castle.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     comedy.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     espnrf.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hdfmas.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     health.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     mobile.abcfamily.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     oscars.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     photos.kaboose.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     photos.babyzone.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     search.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     search.video.movies.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     temail.disneymovieclub.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     tienda.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     topics.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     velti2.disneylandsummer.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     workit.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     999test.abcnews.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     account.toontown.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     casting.disneyparks.jobs.
250.132.181.199.in-addr.arpa. 180 IN    PTR     catalog.disneyuniversity.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     clarity.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     culture.disneyuniversity.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.6abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.abc7.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.abc11.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.abc13.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.abc30.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.7online.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.abc7news.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     finance.abc7chicago.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hotseat.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     missing.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     playdom.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     preview.mydisneyphotopass.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     revenge.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     scandal.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     scrumtv.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     search2.spanish.disneylandsummer.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     theview.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     topics2.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     uplayit.abc7chicago.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     developu.disneyuniversity.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyhd.tv.
250.132.181.199.in-addr.arpa. 180 IN    PTR     polo2011.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     theriver.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     whereami.doit.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     abccomedy.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     helpoffer.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     rugby2011.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     shelterme.6abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     stagepass.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     tenis2011.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     themiddle.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     trongames.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     cougartown.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     devicedata.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneytime.disneyparks.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyvisa.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     experience.disneydestinations.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     happyrides.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     portfolios.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     storefront.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     bodyofproof.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     copavirtual.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     desafioeuro.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyparks.jobs.
250.132.181.199.in-addr.arpa. 180 IN    PTR     familytools.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     glass-house.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hipcricket2.spanish.disneylandsummer.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     klubpenguin.de.
250.132.181.199.in-addr.arpa. 180 IN    PTR     klubpinguin.de.
250.132.181.199.in-addr.arpa. 180 IN    PTR     musiclounge.abc.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     preolimpico.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     radiodisney.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     suburgatory.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     weatherblog.abc13.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     abcdotcomedy.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     euroquiniela.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     happyendings.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     modernfamily.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     sendtofriend.abcnews.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     desafiofutmex.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     dimgpressroom.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneypackage.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneystudios.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     futbolpicante.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     golesdeeuropa.espnfc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     onceuponatime.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     preschooltime.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     rincontecnico.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     yourcommunity.6abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     desafiopremier.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     phineasandferb.disneymags.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyparksblog.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyvisaperks.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     elmejorejemplar.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     lastmanstanding.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     monstroussummer.disneyparks.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     the-glass-house.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyconnection.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     avalanchesoftware.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     celebritywifeswap.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyhumanrights.org.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneysecondscreen.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     watchdisneychannel.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hablemosdefutbolmas.espndeportes.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     mickeystrickortreat.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneylearningstudio.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     shanghaidisneyresort.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneystarbuckssurvey.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyworldsvacations.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     wheelchairrentaldisney.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     hyperionbooksforchildren.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     disneyparksstarbuckssurvey.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.abc.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.test.doit.go.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.fwfest.waltdisneyworld.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.abcfamily.com.
250.132.181.199.in-addr.arpa. 180 IN    PTR     m.bostonmed.abcnews.go.com.

;; AUTHORITY SECTION:
132.181.199.in-addr.arpa. 180   IN      NS      sens01.dig.com.
132.181.199.in-addr.arpa. 180   IN      NS      orns01.dig.com.
132.181.199.in-addr.arpa. 180   IN      NS      sens02.dig.com.
132.181.199.in-addr.arpa. 180   IN      NS      orns02.dig.com.

;; ADDITIONAL SECTION:
orns01.dig.com.         257     IN      A       68.71.223.14
sens02.dig.com.         242     IN      A       199.181.135.199

;; Query time: 7 msec
;; SERVER: 192.168.0.1#53(192.168.0.1)
;; WHEN: Fri Apr 19 23:24:14 2013
;; MSG SIZE  rcvd: 5471

nslookup 199.181.132.250 показывает кучу неавторизованных ответов для разных доменных имен. Но мой пинг не меняется динамически, как ваш.

Это используется для «обратного DNS с прямым подтверждением». Из Википедия

Проверка FCrDNS может создать слабую форму аутентификации, указывающую на наличие действительных отношений между владельцем доменного имени и владельцем сети, которой был предоставлен IP-адрес. Несмотря на свою слабость, эта проверка подлинности достаточно надежна, чтобы ее можно было использовать для внесения в белый список, поскольку спамеры и фишеры обычно не могут обойти эту проверку, когда они используют компьютеры-зомби для подмены почты. То есть обратный DNS может проверить, но обычно он будет частью другого домена, чем заявленное доменное имя.

Тем не менее, я не знаю ни одного приложения, которое на самом деле рассматривает более 1 RR PTR. Возможно, у Disney есть некоторые сервисы, которые смотрят более 1 PTR RR.