[systemd-devel] systemd-resolve SERVFAIL on lookups found by upstream DNS server

[Francesco Belladonna]

Thanks for the input. I speculated it could be a problem related to how my
router is returning some dns queries, given that's the other common piece.
The Fedora laptop has systemd resolve version 246 which is way more up to
date.

What you are saying makes sense though. I reviewed the bugs and it seems to
match perfectly.

On Sat, Apr 17, 2021, 05:11 Mantas Mikulėnas <grawity at gmail.com> wrote:

> On Fri, Apr 16, 2021 at 7:41 PM Francesco Belladonna <francesco at fc5.me>
> wrote:
>
>> Greetings,
>> I’ve been trying to debug why systemd-resolve is not able to perform nslookup
>> static-exp1.licdn.com.
>> Altering /etc/resolv.conf to point directly to the DNS server (or my
>> router in this case) solves the problem, which seems to suggest the problem
>> is isolated to systemd-resolve.
>> The problem is identical on both my laptops which are running 2 different
>> O.S. (Kubuntu 18.04 and Fedora 33).
>> The entire DNS configuration is provided by the router acting as DHCP
>> server.
>>
>> The system I’m performing my tests is Kubuntu, where the systemd version
>> is:
>>
>> systemd --version
>> systemd 237
>> +PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid
>>
>> SYSTEMD_LOG_LEVEL is set to debug.
>> Is there any other useful tool I can use to debug this further?
>> The problematic domain is static-exp1.licdn.com which is the CDN for
>> LinkedIn. I have no idea why *this* specific domain is affected.
>>
> Most likely because it has one of those *interesting* CNAME chains:
>
> $ rdt static-exp1.licdn.com
> static-exp1.licdn.com = 2-01-2c3e-003d.cdx.cedexis.net
>    2-01-2c3e-003d.cdx.cedexis.net = li-prod-static.azureedge.net
>       li-prod-static.azureedge.net = li-prod-static.afd.azureedge.net
>          li-prod-static.afd.azureedge.net =
> star-azureedge-prod.trafficmanager.net
>             star-azureedge-prod.trafficmanager.net =
> dual.t-0009.t-msedge.net
>                dual.t-0009.t-msedge.net = t-0009.t-msedge.net
>                   t-0009.t-msedge.net =
> Edge-Prod-LON21r3.ctrl.t-0009.t-msedge.net
>                      edge-prod-lon21r3.ctrl.t-0009.t-msedge.net =
> standard.t-0009.t-msedge.net
>                         standard.t-0009.t-msedge.net = 13.107.213.19,
> 13.107.246.19, 2620:1ec:46::19, 2620:1ec:bdf::19
>
> (Though sometimes it's shorter, pointing at epsiloncdn instead of Azure.
> It depends on where you're making the query from.)
>
> I *think* this was fixed in git a few weeks ago. There's already an
> Ubuntu bug report for the same issue:
> https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1921636
>
> --
> Mantas Mikulėnas
>
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