Inbound UDP not working

user115 · February 15, 2022, 3:33am

Hi, I’m experimenting with fly.io as an authoritative DNS platform. I’m running nsd with a standalone configuration. After my server starts, it’s reachable over TCP (e.g. with dig +tcp @myserver) but not UDP. If I connect to the console with SSH and use dig against localhost and the IP everything works as expected.

My fly.toml file looks like this:

app = "mydnstestapp"

kill_signal = "SIGINT"
kill_timeout = 5

[[services]]
  internal_port = 53
  protocol = "udp"

  [[services.ports]]
    port = 53

[[services]]
  internal_port = 53
  protocol = "tcp"

  [[services.ports]]
    port = 53

Any pointers appreciated

jsierles · February 15, 2022, 11:33am

Can you paste your server config? You may need to explicitly bind to :: or to fly-global-services.

user115 · February 15, 2022, 1:52pm

Hi! Thanks so much for the reply. I have the ip-address sections commented out, the defaults should be to bind to all local interfaces. It looks like this:

# uncomment to specify specific interfaces to bind (default are the
	# wildcard interfaces 0.0.0.0 and ::0).
	# For servers with multiple IP addresses, list them one by one,
	# or the source address of replies could be wrong.
	# Use ip-transparent to be able to list addresses that turn on later.
	# ip-address: 1.2.3.4
	# ip-address: 1.2.3.4@5678
	# ip-address: 12fe::8ef0

	# Allow binding to non local addresses. Default no.
	#ip-transparent: yes

	# Allow binding to addresses that are down.  Default no.
	#ip-freebind: no

	# use the reuseport socket option for performance. Default no.
	#reuseport: yes

	# enable debug mode, does not fork daemon process into the background.
	debug-mode: no

	# listen on IPv4 connections
	do-ip4: yes

	# listen on IPv6 connections
	do-ip6: yes

	# port to answer queries on. default is 53.
	port: 53

jsierles · February 15, 2022, 8:51pm

Can you try with fly-global-services in the ip-address? If it doesn’t like hostnames, try using the equivalent value from /etc/hosts.

user115 · February 15, 2022, 9:08pm

Aha, I didn’t think to check /etc/hosts… I tried telling it to bind to fly-global-services and it said it was an unknown address, I’ll see what I can find in /etc/hosts.

Thanks so much for your help!

user115 · February 15, 2022, 9:20pm

This is what I see checking the container directly:

Connecting to top1.nearest.of.k-flydns.internal... complete
/ # cat /etc/hosts
127.0.0.1	localhost localhost.localdomain
::1		localhost localhost.localdomain

127.0.0.1	localhost localhost4

::1	localhost localhost6

# Address used for global traffic routing
172.19.1.139	fly-global-services

# Address in the 6PN private network for this app
fdaa:0:4d3d:a7b:87:f31:bf49:2	0f31bf49.vm.k-flydns.internal 0f31bf49 fly-local-6pn
/ # ifconfig -a
dummy0    Link encap:Ethernet  HWaddr 72:2D:A6:B0:AA:B3
          BROADCAST NOARP  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

eth0      Link encap:Ethernet  HWaddr DE:AD:35:F2:D3:72
          inet addr:172.19.1.138  Bcast:172.19.1.143  Mask:255.255.255.248
          inet6 addr: fe80::dcad:35ff:fef2:d372/64 Scope:Link
          inet6 addr: fdaa:0:4d3d:a7b:87:f31:bf49:2/112 Scope:Global
          inet6 addr: 2604:1380:4510:401:0:f31:bf49:1/127 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1420  Metric:1
          RX packets:823 errors:0 dropped:0 overruns:0 frame:0
          TX packets:835 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:81126 (79.2 KiB)  TX bytes:81129 (79.2 KiB)

Looks like I’ll bind an address that isn’t assigned, so I’ll need to enable ip-transparent

I’ll give it a whirl and see if it works, thanks again.

user115 · February 15, 2022, 10:34pm

Hm, still no luck talking to it over UDP through the proxy. If I connect to the console I can run dig and things work.

It’d be neat if this worked, would be a simple path to BIND zonefile-compatible anycast DNS. Thanks for any advice.

my fly.toml:


kill_signal = "SIGINT"
kill_timeout = 5

[[services]]
  internal_port = 53
  protocol = "udp"

  [[services.ports]]
    port = 53

[[services]]
  internal_port = 53
  protocol = "tcp"

  [[services.ports]]
    port = 53

my (super ugly, ewwww) Dockerfile:


RUN apk --update --no-cache add nsd

LABEL maintainer="jw"

COPY /zones /etc/nsd/zones/
COPY /nsd.conf /etc/nsd/
COPY /includes /etc/nsd/includes/

RUN mkdir -p /var/lib/nsd
RUN chown nsd:nsd /var/lib/nsd
RUN chmod 0755 /var/lib/nsd

EXPOSE 53/tcp
EXPOSE 53/udp

#ENTRYPOINT [ "/usr/sbin/nsd","-d" ]

CMD [ "/usr/sbin/nsd", "-d" ]

my nsd.conf (first part):

	# Number of NSD servers to fork.  Put the number of CPUs to use here.
	#server-count: 2

	# uncomment to specify specific interfaces to bind (default are the
	# wildcard interfaces 0.0.0.0 and ::0).
	# For servers with multiple IP addresses, list them one by one,
	# or the source address of replies could be wrong.
	# Use ip-transparent to be able to list addresses that turn on later.
	# ip-address: 1.2.3.4
	# ip-address: 1.2.3.4@5678
	# ip-address: 12fe::8ef0
	ip-address: 172.19.1.139
	ip-address: ::

	# Allow binding to non local addresses. Default no.
	ip-transparent: yes

	# Allow binding to addresses that are down.  Default no.
	#ip-freebind: no

	# use the reuseport socket option for performance. Default no.
	reuseport: yes

	# enable debug mode, does not fork daemon process into the background.
	debug-mode: no

	# listen on IPv4 connections
	do-ip4: yes

	# listen on IPv6 connections
	do-ip6: yes

	# port to answer queries on. default is 53.
	port: 53

ifconfig on the container looks like:

/ # ifconfig -a
dummy0    Link encap:Ethernet  HWaddr C2:6C:93:05:68:78
          BROADCAST NOARP  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

eth0      Link encap:Ethernet  HWaddr DE:AD:E0:1F:AB:10
          inet addr:172.19.9.186  Bcast:172.19.9.191  Mask:255.255.255.248
          inet6 addr: 2604:1380:4510:500:0:6fd1:1352:1/127 Scope:Global
          inet6 addr: fe80::dcad:e0ff:fe1f:ab10/64 Scope:Link
          inet6 addr: fdaa:0:4d3d:a7b:85:6fd1:1352:2/112 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1420  Metric:1
          RX packets:75 errors:0 dropped:0 overruns:0 frame:0
          TX packets:77 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:10088 (9.8 KiB)  TX bytes:9037 (8.8 KiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

/etc/hosts:

127.0.0.1	localhost localhost.localdomain
::1		localhost localhost.localdomain

127.0.0.1	localhost localhost4

::1	localhost localhost6

# Address used for global traffic routing
172.19.9.187	fly-global-services

# Address in the 6PN private network for this app
fdaa:0:4d3d:a7b:85:6fd1:1352:2	6fd11352.vm.k-flydns.internal 6fd11352 fly-local-6pn

kurt · February 15, 2022, 11:17pm

That internal IP changes each time your VM runs. You’ll need to generate your nsd.conf at boot time to get that IP in there.

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Inbound UDP not working

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