Does not listen port 53

[jkman2]

Fresh Lbuntu 17.10 install in Virtual box. No error on compilation.

I run
sudo ./dnsseed -h dnsseed -n localhost -m test. -p 53
...
Starting 4 DNS threads for dnsseed on localhost (port 53).......done
...

but
nslookup dnsseed localhost
;; connection timed out; no server could be reached

[jkman2]

This is where it stops.
ssize_t insize = recvmsg(listenSocket, &msg, 0);

[jonasschnelli]

Does the same happen if you run non sudo on port 5353?
Can you attach gdb and get a strack trace?

[jkman2]

UDP port 5353 is already in use. TCP port 5353 is closed. 5353 is default port for multicast DNS.
netcat -z -v -u localhost 5353
Connection to localhost 5353 port [udp/mdns] succeeded!

If I use port 5555 or 50 dnsseed opens that UDP port.

Port 50 works with sudo.
netcat -z -v -u localhost 50
Connection to localhost 50 port [udp/re-mail-ck] succeeded!

UFW is inactive.
sudo ufw status
Status: inactive

Iptables is empty.

[jkman2]

I need to learn how to use GDB.

Eg. port 5555 or 55 is listened only by IPv6. Port 53 will not appear in netstat list.

netstat -plnu
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           -                   
udp        0      0 0.0.0.0:5355            0.0.0.0:*                           -                   
udp        0      0 0.0.0.0:57611           0.0.0.0:*                           -                   
udp        0      0 127.0.0.53:53           0.0.0.0:*                           -                   
udp        0      0 0.0.0.0:68              0.0.0.0:*                           -                   
udp6       0      0 :::5353                 :::*                                -                   
udp6       0      0 :::5355                 :::*                                -                   
udp6       0      0 :::43253                :::*                                -                   
udp6       0      0 :::5555                 :::*        

If I run
sudo netcat -l -u 53

Port 53 is working OK.
netcat -z -v -u localhost 53
Connection to localhost 53 port [udp/domain] succeeded!

Additional info...

If I run dnsseed on port 55 and make a redirect
sudo iptables -t nat -A OUTPUT -o lo -p udp --dport 53 -j REDIRECT --to-port 55
it works

 nslookup seedtest localhost
Server:		127.0.0.53
Address:	127.0.0.53#53

Name:	seedtest
Address: 62.210.253.10
Name:	seedtest
Address: 109.69.78.107
Name:	seedtest

but this brakes the sever's dns.

 nslookup google.com

;; Warning: query response not set
Server:		127.0.0.53
Address:	127.0.0.53#53

** server can't find google.com: REFUSED

[jkman2]

systemd-resolved is added to Ubuntu 16.10 ->. 127.0.0.53:53 causes problems.

I think bitcoin seeder need to be binded to listen only specified IP address like '-b 10.0.2.15'.