Per @aborrero's comments on IRC about T202886: cloudvps: eqiad1: create DNS PTR records for cloud addresses, I just SSH'd to eqiad1.bastion.wmflabs.org and confirmed that something is wrong here:
krenair@bastion-eqiad1-01:~$ ip addr | grep 172
inet 172.16.1.136/21 brd 172.16.7.255 scope global eth0
krenair@bastion-eqiad1-01:~$ host 172.16.1.136
Host 136.1.16.172.in-addr.arpa. not found: 3(NXDOMAIN)
krenair@bastion-eqiad1-01:~$ dig 136.1.16.172.in-addr.arpa. PTR
; <<>> DiG 9.10.3-P4-Debian <<>> 136.1.16.172.in-addr.arpa. PTR
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 9148
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;136.1.16.172.in-addr.arpa. IN PTR
;; AUTHORITY SECTION:
16.172.in-addr.arpa. 718 IN SOA localhost. root. 1 604800 86400 2419200 604800
;; Query time: 0 msec
;; SERVER: 208.80.155.118#53(208.80.155.118)
;; WHEN: Tue Aug 28 22:19:43 UTC 2018
;; MSG SIZE rcvd: 92
krenair@bastion-eqiad1-01:~$ dig 136.1.16.172.in-addr.arpa. PTR @labs-ns0.wikimedia.org
; <<>> DiG 9.10.3-P4-Debian <<>> 136.1.16.172.in-addr.arpa. PTR @labs-ns0.wikimedia.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40775
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 2800
;; QUESTION SECTION:
;136.1.16.172.in-addr.arpa. IN PTR
;; Query time: 2 msec
;; SERVER: 208.80.155.117#53(208.80.155.117)
;; WHEN: Tue Aug 28 22:19:53 UTC 2018
;; MSG SIZE rcvd: 54Somewhere in Designate I recall there being a special zone like 10.in-addr.arpa. (may have required some special rights/headers to get to that, maybe sudo to a special tenant which I've forgotten the name of) that nova managed PTR records under, there should be something similar for 172.in-addr.arpa.