Facebook Outage: Yes, its DNS (sort of). A super quick analysis of what is going on.

Published: 2021-10-04
Last Updated: 2021-10-04 18:23:45 UTC
by Johannes Ullrich (Version: 1)
8 comment(s)

For the Billions out there still wasting time on Facebook: Enjoy your increased productivity while many Facebook properties (Facebook, Instagram, WhatsApp) are down.

More readable summary of the analysis below: The BGP routes pointing traffic to Facebook's IP address space have been withdrawn. The Internet no longer knows where to find Facebook's IPs. One symptom is that DNS requests are failing. But this is just the result of Facebook hosting its DNS servers inside its own network. Even with working DNS (for example if you still have cached results), the IPs are currently not reachable


Here is a quick view of what may have happened.

1 - Does facebook.com resolve?

% host facebook.com
facebook.com has address
facebook.com has IPv6 address 2a03:2880:f141:82:face:b00c:0:25de
facebook.com mail is handled by 2560 smtpin.vvv.facebook.com.

% host www.facebook.com
www.facebook.com is an alias for star-mini.c10r.facebook.com.
star-mini.c10r.facebook.com has address
star-mini.c10r.facebook.com has IPv6 address 2a03:2880:f138:83:face:b00c:0:25de

Yes! (at least for me, it does). But was that just a cached response? Let's follow the DNS chain.

2. What is the NS record for facebook.com according to the .com zone?

(abbreviated output)


% dig NS facebook.com @h.gtld-servers.net


;; AUTHORITY SECTION: facebook.com. 172800 IN NS a.ns.facebook.com. facebook.com. 172800 IN NS b.ns.facebook.com. facebook.com. 172800 IN NS c.ns.facebook.com. facebook.com. 172800 IN NS d.ns.facebook.com. ;; ADDITIONAL SECTION: a.ns.facebook.com. 172800 IN A a.ns.facebook.com. 172800 IN AAAA 2a03:2880:f0fc:c:face:b00c:0:35 b.ns.facebook.com. 172800 IN A b.ns.facebook.com. 172800 IN AAAA 2a03:2880:f0fd:c:face:b00c:0:35 c.ns.facebook.com. 172800 IN A c.ns.facebook.com. 172800 IN AAAA 2a03:2880:f1fc:c:face:b00c:0:35 d.ns.facebook.com. 172800 IN A d.ns.facebook.com. 172800 IN AAAA 2a03:2880:f1fd:c:face:b00c:0:35

3. Let's use one of these NS records

% dig NS facebook.com @
; <<>> DiG 9.10.6 <<>> NS facebook.com @
;; global options: +cmd
;; connection timed out; no servers could be reached

4. So let's see why we can't reach these servers

% traceroute
traceroute to (, 64 hops max, 52 byte packets
 1  [redacted]  0.628 ms  0.159 ms  0.101 ms
 2  [redacted]  2.333 ms  1.715 ms  1.706 ms
 3 (  9.123 ms  10.691 ms  10.338 ms
 4 (  9.254 ms  8.754 ms  10.311 ms
 5  ae-13-ar02.westside.fl.jacksvil.comcast.net (  9.332 ms  11.930 ms  9.746 ms
 6  be-33622-cs02.56marietta.ga.ibone.comcast.net (  23.797 ms
 7  be-2112-pe12.56marietta.ga.ibone.comcast.net (  24.322 ms
 8  * * *

So Comcast doesn't know how to reach Facebook. Well... BGP should tell them

5. Let's check with a BGP Looking Glass

show router bgp routes ipv4 hunt 
BGP Router ID: AS:3356 Local AS:3356 
Legend - 
Status codes : u - used, s - suppressed, h - history, d - decayed, * - valid 
l - leaked, x - stale, > - best, b - backup, p - purge 
Origin codes : i - IGP, e - EGP, ? - incomplete 

BGP IPv4 Routes 
No Matching Entries Found. 

So looks like the route is gone. Oh well. Enjoy while it lasts.



Johannes B. Ullrich, Ph.D. , Dean of Research, SANS.edu

Keywords: facebook dns bgp
8 comment(s)


Great post, would have been nice to include an example of the expected BGP looking glass response, but, good stuff. Thanks.
I probably should do a BGP looking glass diary one of these days.
Johannes, could you follow up with samples now that they are coming back online?
Partial current response

show route protocol bgp detail
inet.0: 978837 destinations, 4534922 routes (978704 active, 0 holddown, 50386 hidden) (6 entries, 1 announced)

*BGP Preference: 170/-87
Next hop type: Indirect, Next hop index: 0
Address: 0xb1f8e5c
Next-hop reference count: 220325
Next hop type: Router, Next hop index: 11388
Next hop: via ae0.11, selected
Label element ptr: 0xae62f80
Label parent element ptr: 0x0
Label element references: 2
Label element child references: 1
Label element lsp id: 0
Session Id: 0x2e1
Protocol next hop:
Indirect next hop: 0xb114700 2097160 INH Session ID: 0x30f
Local AS: 3356 Peer AS: 3356
Age: 1w6d 13:26:59 Metric: 100000 Metric2: 20
Validation State: unverified
Task: BGP_3356.
Announcement bits (5): 0-KRT 9-BGP_RT_Background 10-Resolve tree 4 11-RT 12-Resolve tree 5
AS path: 32934 I
Communities: 3356:3 3356:86 3356:575 3356:666 3356:2006 3356:2016 3356:11222 3356:12189 3549:600 65000:64980 65000:64987
Localpref: 86
Router ID:
In case anyone was looking for a looking glass, Verizon provides one here: https://enterprise.verizon.com/why-verizon/looking-glass/.

Of course, there are lots of others: https://www.bgp4.as/looking-glasses

Happy quiet day, all (with less social fog)... ;0)
May it be an attack ?
Thanks Johannes, this is a really useful and clear breakdown. One quick question - was there any particular reason you opted to dig NS facebook.com @h.gtld-servers.net as opposed to any of the others? Thanks
Thank you Johannes for the troubleshooting details (and also for your great podcast series!)

Hard to see if it was part of an attack when the route just simply stopped to get advertised to provider, unless the Facebook edge routers went down due to DDoS or some other service denial attack.

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