DNS not resolving for a particular domain only

Mark Andrews marka at isc.org
Mon Aug 21 23:56:25 UTC 2017


In message <93595848.2099571.1503336849573 at mail.yahoo.com>, U Zee writes:
> Thanks Mark,
> So mysteriously the problem is now gone and I have no idea how, I know
> that I didn't change anything.
> While investigating, I tried looking but didn't get anything in packet
> capture on the recursive server, I think mainly because I had to grep for
> something otherwise there was just too much traffic. So its possible, my
> grep for lenovo didn't show related packets.... But I will never know now 

A single missing routing entry could have taken the site down.  The
delegation for lnvcdn.net only has 2 of the 4 nameservers listed
and those 2 are in the same /24.  There is a reason that it is
recommended that there are multiple nameservers which are geographically
and topologically dispersed are used and that both sides of the
delegation have consistent NS and address records.  It reduces the
probability that single faults cause failures like this.

Mark

;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7439
;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 6, ADDITIONAL: 3

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
;; QUESTION SECTION:
;lnvcdn.net.			IN	NS

;; AUTHORITY SECTION:
lnvcdn.net.		172800	IN	NS	ns1.lnvcdn.net.
lnvcdn.net.		172800	IN	NS	ns2.lnvcdn.net.
A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. 86400 IN NSEC3 1 1 0 - A1RUUFFJKCT2Q54P78F8EJGJ8JBK7I8B  NS SOA RRSIG DNSKEY NSEC3PARAM
A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. 86400 IN RRSIG NSEC3 8 2 86400 20170825051539 20170818040539 57899 net. ZbkC2I24NO+y91E+sPWOADqbjsVpHfuFhnox5QfeuImFsL2z0x3X+UG6 Lt9emQ23VFesgs8+J1WQVjHHBuhvc1XdWG7jBpv3Tr776oBcSF5rrqMp zC5CjRIzOlojSVpNG3snkW0xfijBuOl51RzaKrSqKb2x/tcXWUWkHpDw ga8=
2K5T76ECDUK1RJEDVHKHNL0LCCENKMES.net. 86400 IN NSEC3 1 1 0 - 2K673TEK531CUGB8J9QHASJNDFOVU87L  NS DS RRSIG
2K5T76ECDUK1RJEDVHKHNL0LCCENKMES.net. 86400 IN RRSIG NSEC3 8 2 86400 20170828050756 20170821035756 57899 net. s905nQwEBRv9cbVzZMWFLfb0Jnq/K+R32MJdnYa9CaPpJCtGIMzWkmPt yl7MKawRlhJE01n4ll4/4Grj3asVi5/LsrGSH7bjO9GkclWqsuxoeepl JrUh/UkZFw5qhnCvw1teWAPcZ6T93DBmq02c8UemFAYRrMO1ugbvHGQo QPw=

;; ADDITIONAL SECTION:
ns1.lnvcdn.net.		172800	IN	A	192.16.0.5
ns2.lnvcdn.net.		172800	IN	A	192.16.0.6

;; Query time: 257 msec
;; SERVER: 2001:503:d414::30#53(2001:503:d414::30)
;; WHEN: Tue Aug 22 09:45:04 AEST 2017
;; MSG SIZE  rcvd: 592

;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22513
;; flags: qr aa; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 5

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
;; QUESTION SECTION:
;lnvcdn.net.			IN	NS

;; ANSWER SECTION:
lnvcdn.net.		3600	IN	NS	ns1.lnvcdn.net.
lnvcdn.net.		3600	IN	NS	ns3.lnvcdn.net.
lnvcdn.net.		3600	IN	NS	ns4.lnvcdn.net.
lnvcdn.net.		3600	IN	NS	ns2.lnvcdn.net.

;; ADDITIONAL SECTION:
ns1.lnvcdn.net.		3600	IN	A	192.16.0.5
ns2.lnvcdn.net.		3600	IN	A	192.16.0.6
ns3.lnvcdn.net.		3600	IN	A	198.7.30.5
ns4.lnvcdn.net.		3600	IN	A	198.7.30.6

;; Query time: 12 msec
;; SERVER: 192.16.0.5#53(192.16.0.5)
;; WHEN: Tue Aug 22 09:45:04 AEST 2017
;; MSG SIZE  rcvd: 175

>       From: Mark Andrews <marka at isc.org>
>  To: U Zee <uzee001 at yahoo.com>
> Cc: Grant Taylor <gtaylor at tnetconsulting.net>; "bind-users at lists.isc.org"
> <bind-users at isc.org>
>  Sent: Monday, August 14, 2017 3:00 AM
>  Subject: Re: DNS not resolving for a particular domain only
>
>
> In message <1396839156.197734.1502489970286 at mail.yahoo.com>, U Zee via
> bind-users writ
> es:
> > Thanks for the suggestion Grant.
> > Here's what I get for the recursive server's capture: ( I queried from
> > the recursive server itself from another ssh session so it is the client
> > as well)
> >
> > # tcpdump -v -v -nt -i eth0 udp port 53|grep lenovotcpdump: listening on
> > eth0, link-type EN10MB (Ethernet), capture size 65535 bytes   
> >    86.36.AA.BB.45776 > 86.36.AA.CC.domain: [bad udp cksum 8a1b!] 34468+
> A? www.lenovo.com. (32)
> >    86.36.AA.BB.45776 > 86.36.AA.CC.domain: [bad udp cksum 8a1b!] 34468+
> A? www.lenovo.com. (32)
> >    86.36.AA.BB.36143 > 193.108.91.79.domain: [bad udp cksum c63c!]
> 12966 [1au] A?
> > www.lenovo.com. ar: . OPT UDPsize=4096 OK (43)
> >    193.108.91.79.domain > 86.36.AA.BB.36143: [udp sum ok] 12966*- q: A?
> www.lenovo.com. 1/0/1 www.lenovo.com. CNAME cs47.can.lnvcdn.net. ar: .
> OPT UDPsize=4096 OK (76) 
> >    86.36.AA.BB.45776 > 86.36.AA.CC.domain: [bad udp cksum 8a1b!] 34468+
> A? www.lenovo.com. (32)
> >    86.36.AA.BB.10224 > 86.36.DD.EE.domain: [badudp cksum 18c7!] 12721
> [1au] A? www.lenovo.com.ourdomain.com. ar: . OPT UDPsize=4096 OK (57)
> >    86.36.DD.EE.domain > 86.36.AA.BB.10224: [udp sum ok] 12721
> NXDomain*- q: A? www.lenovo.com.ourdomain.com. 0/1/1 ns: ourdomain.com.
> SOA master.ourdomain.com. host-master.ourparentdomain.com. 138524105 900
> 450 3600000 60 ar: . OPT UDPsize=4096 OK (138)   
> >    86.36.AA.CC.domain > 86.36.AA.BB.45776: [udp sum ok] 34468 ServFail
> q: A? www.lenovo.com. 0/0/0 (32)
> >
> > 86.36.AA.BB = localhost (our recursive server) where I ran the query and
> > capture
> > 86.36.AA.CC = our secondary recursive server (no idea why that was
> > contacted)
> > 86.36.DD.EE = our one of two anycast addresses which point to the
> > recursive servers
> >
> >
> > So it looks like we do get to the CNAME (4th line) but still it
> > fails...?I also tried a capture from a regular linux client but the
> > output was similar except that it didn't include the CNAME line.
>
> Well the next stage is to trace what happens when the recursive
> server looks for cs47.can.lnvcdn.net, the target of the CNAME.
>
> Mark
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                INTERNET: marka at isc.org

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org


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