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<p class="MsoNormal">Subject: DNSMASQ failing to return SRV records with loss of communication to a single DNS server<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Issue: We have SIP SRV records for a domain which can be provided by two DNS servers in our environment. During testing we have noticed that if one of the DNS servers is un-reachable, the request for the SRV records via dnsmasq times
out.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNoSpacing">This only happens when the query is originated from outside the box where dnsmasq is running. IE – if we issue the SRV query from the dnsmasq server, the SRV records are returned. If we issue the request from a client VM which is set
to resolve queries against our dnsmasq host – the request times out.<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">Note: some of the information below has been changed/replaced with xxx, such as IP addresses and domain names for security reasons.<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">Dnsmasq.conf has the following entries – indicating to forward requests for labdomain.net to 10.xx.xx.12 and 10.xx.xx.20. <o:p></o:p></p>
<p class="MsoNoSpacing">server=/labdomain.net/10.xx.xx.12<o:p></o:p></p>
<p class="MsoNoSpacing">server=/labdomain.net/10.xx.xx.20<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">VM making SRV queries is 10.xx.xx.99<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing"><b>When we query for an SRV record with 10.xx.xx.5 being our DNSMASQ server, and have commented out the non-reachable DNS server: 10.xx.xx.12 – we receive a response to the SRV query.<o:p></o:p></b></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">#server=/labdomain.net/10.xx.xx.12<o:p></o:p></p>
<p class="MsoNoSpacing">server=/labdomain.net/10.xx.xx.20<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">[labuser@f5-test ~]$ dig srv _sip._udp.scscf.sprout.lp.labdomain.net @10.xx.xx.5<o:p></o:p></p>
<p class="MsoNoSpacing">;; Truncated, retrying in TCP mode.<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.62.rc1.el6_9.5 <<>> srv _sip._udp.scscf.sprout.lp.labdomain.net @10.xx.xx.5<o:p></o:p></p>
<p class="MsoNoSpacing">;; global options: +cmd<o:p></o:p></p>
<p class="MsoNoSpacing">;; Got answer:<o:p></o:p></p>
<p class="MsoNoSpacing">;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14584<o:p></o:p></p>
<p class="MsoNoSpacing">;; flags: qr aa; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 5<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">;; QUESTION SECTION:<o:p></o:p></p>
<p class="MsoNoSpacing">;_sip._udp.scscf.sprout.lp.labdomain.net. IN SRV<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">;; ANSWER SECTION:<o:p></o:p></p>
<p class="MsoNoSpacing">_sip._udp.scscf.sprout.lp.labdomain.net. 15 IN SRV 10 50 5054 ovpklp-viscscf-spn-05.labdomain.net.<o:p></o:p></p>
<p class="MsoNoSpacing">_sip._udp.scscf.sprout.lp.labdomain.net. 15 IN SRV 10 50 5054 ovpklp-viscscf-spn-01.labdomain.net.<o:p></o:p></p>
<p class="MsoNoSpacing">_sip._udp.scscf.sprout.lp.labdomain.net. 15 IN SRV 10 50 5054 ovpklp-viscscf-spn-02.labdomain.net.<o:p></o:p></p>
<p class="MsoNoSpacing">_sip._udp.scscf.sprout.lp.labdomain.net. 15 IN SRV 10 50 5054 ovpklp-viscscf-spn-03.labdomain.net.<o:p></o:p></p>
<p class="MsoNoSpacing">_sip._udp.scscf.sprout.lp.labdomain.net. 15 IN SRV 10 50 5054 ovpklp-viscscf-spn-04.labdomain.net.<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">;; ADDITIONAL SECTION:<o:p></o:p></p>
<p class="MsoNoSpacing">ovpklp-viscscf-spn-05.labdomain.net. 43200 IN A 10.xx.xx.18<o:p></o:p></p>
<p class="MsoNoSpacing">ovpklp-viscscf-spn-01.labdomain.net. 43200 IN A 10.xx.xx.14<o:p></o:p></p>
<p class="MsoNoSpacing">ovpklp-viscscf-spn-02.labdomain.net. 43200 IN A 10.xx.xx.15<o:p></o:p></p>
<p class="MsoNoSpacing">ovpklp-viscscf-spn-03.labdomain.net. 43200 IN A 10.xx.xx.16<o:p></o:p></p>
<p class="MsoNoSpacing">ovpklp-viscscf-spn-04.labdomain.net. 43200 IN A 10.xx.xx.17<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">;; Query time: 2 msec<o:p></o:p></p>
<p class="MsoNoSpacing">;; SERVER: 10.xx.xx.5#53(10.xx.xx.5)<o:p></o:p></p>
<p class="MsoNoSpacing">;; WHEN: Mon Aug 13 16:34:40 2018<o:p></o:p></p>
<p class="MsoNoSpacing">;; MSG SIZE rcvd: 528<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNoSpacing"><b>When we query for an SRV record with 10.xx.xx.5 being our DNSMASQ server, and have both the good and non-reachable DNS server in play – we receive a timeout to the SRV query. In this case – 10.xx.xx.20 is fully capable of responding
to the SRV query.<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNoSpacing">server=/labdomain.net/10.xx.xx.12 <span style="font-family:Wingdings">
ß</span> not reachable<o:p></o:p></p>
<p class="MsoNoSpacing">server=/labdomain.net/10.xx.xx.20<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">[labuser@f5-test ~]$ dig srv _sip._udp.scscf.sprout.lp.labdomain.net @10.xx.xx.5<o:p></o:p></p>
<p class="MsoNoSpacing">;; Truncated, retrying in TCP mode.<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
<p class="MsoNoSpacing">; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.62.rc1.el6_9.5 <<>> srv _sip._udp.scscf.sprout.lp.labdomain.net @10.xx.xx.5<o:p></o:p></p>
<p class="MsoNoSpacing">;; global options: +cmd<o:p></o:p></p>
<p class="MsoNoSpacing">;; connection timed out; no servers could be reached<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dnsmasq logging shows:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Aug 14 16:22:14 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5161]: query[SRV] _sip._udp.scscf.sprout.lp.labdomain.net from 10.xx.xx.99<o:p></o:p></p>
<p class="MsoNormal">Aug 14 16:22:14 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5161]: forwarded _sip._udp.scscf.sprout.lp.labdomain.net to 10.xx.xx.12<o:p></o:p></p>
<p class="MsoNormal">Aug 14 16:22:14 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5161]: forwarded _sip._udp.scscf.sprout.lp.labdomain.net to 10.xx.xx.20<o:p></o:p></p>
<p class="MsoNormal">Aug 14 16:22:14 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5161]: nameserver 10.xx.xx.20 refused to do a recursive query<o:p></o:p></p>
<p class="MsoNormal">Aug 14 16:22:14 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5172]: query[SRV] _sip._udp.scscf.sprout.lp.labdomain.net from 10.xx.xx.99<o:p></o:p></p>
<p class="MsoNormal">Aug 14 16:22:24 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5173]: query[SRV] _sip._udp.scscf.sprout.lp.labdomain.net from 10.xx.xx.99<o:p></o:p></p>
<p class="MsoNormal">Aug 14 16:22:34 vsmslp-az2-dev-dnsmasq1-mgt dnsmasq[5174]: query[SRV] _sip._udp.scscf.sprout.lp.labdomain.net from 10.xx.xx.99<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I could use some ideas on how to further troubleshoot this issue.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-right:5.8pt"><b><span style="font-family:"Arial",sans-serif;color:black">Andy Warner</span></b><span style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-right:5.8pt"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black">Telecom Design Engineer</span><span style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-right:5.8pt"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black">O: 406-752-3330 / M: 913-972-7521</span><span style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-right:5.8pt"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black">andrew.c.warner@sprint.com</span><span style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><img width="335" height="60" id="Picture_x0020_1" src="cid:image001.png@01D433B6.EDBA9700" alt="cid:408000_086801428601138001@pvmxe13g01"><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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