comcast.com DNSSEC Outage: 2017-09-28

Date: September 28, 2017

Overview

This page gives some details on the comcast.com DNSSEC outage on September 28, 2017.

Timeline / DNSViz

DNSSEC Debugger

Unlike DNSViz, Verisign's DNSSEC Debugger doesn't archive results, so here's a screenshot of my web browser's output from September 28, 2017:

September 28, 2017 comcast.com DNSSEC outage

Zonemaster

dnscheck

Note: dnscheck requires javascript.

drill trace

Since DNSSEC contains so much garbage, I put the complete drill trace into its own file, with the relevant portion below (emphasis added):

;; Domain: comcast.com.
;; Signature ok but no chain to a trusted key or ds record
[S] comcast.com. 3600 IN DNSKEY 256 3 5 ;{id = 57570 (zsk), size = 1024b}
comcast.com. 3600 IN DNSKEY 257 3 5 ;{id = 35356 (ksk), size = 2048b}
[S] comcast.com. 120 IN A 69.252.80.75
;;[S] self sig OK; [B] bogus; [T] trusted

Google Public DNS: with and without DNSSEC

DNSSEC can be disabled in queries via the CD (checking disabled) bit. Let's compare DNS queries with and without DNSSEC.

With DNSSEC, DNS queries fail:

$ dig +dnssec a comcast.com. @8.8.8.8

; <<>> DiG 9.4.2-P2 <<>> +dnssec a comcast.com. @8.8.8.8
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 55287
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 512
;; QUESTION SECTION:
;comcast.com. IN A

;; Query time: 89 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Thu Sep 28 13:59:17 2017
;; MSG SIZE rcvd: 40


You have to disable DNSSEC to make DNS queries work:

$ dig +cd a comcast.com. @8.8.8.8

; <<>> DiG 9.4.2-P2 <<>> +cd a comcast.com. @8.8.8.8
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53327
;; flags: qr rd ra cd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;comcast.com. IN A

;; ANSWER SECTION:
comcast.com. 119 IN A 69.252.80.75

;; Query time: 39 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Thu Sep 28 13:59:17 2017
;; MSG SIZE rcvd: 45

Logfile examples