How do you turn OFF, or reduce priority of, IPv6 connect attempts by submission relay?
On 4/3/21 8:03 PM, PGNet Dev wrote:
my server is a linux, dual-stack IPv4/IPv6 host
it runs multiple services, including, but not limited to, postfix & dovecot
the hostname is
internal.mx.example.com
its DNS config,
host internal.mx.example.com internal.mx.example.com has address 10.1.1.15 internal.mx.example.com has IPv6 address fd80:10:1::15 internal.mx.example.com mail is handled by 5 internal.mx.example.com.
here, for dovecot
dovecot --version 2.3.13 (89f716dc2)
submission is configured to relay to the same-host postfix instance, listening @ port 465
./conf.d/10-master.conf ... protocols = imap submission lmtp sieve ... submission_relay_host = internal.mx.example.com submission_relay_port = 465 submission_relay_ssl = smtps submission_relay_ssl_verify = yes submission_relay_trusted = yes
whereas other services listen at both IPv4 & IPv6 addresses, with IPv6 preferred over IPv4, postfix listens ONLY on IPv4,
postconf inet_protocols inet_protocols = ipv4
and, as intended, simply refuses ipv6 connections
telnet 10.1.1.15 465 Trying 10.1.1.15... Connected to 10.1.1.15. Escape character is '^]'. ^] telnet> quit Connection closed.
telnet -6 fd80:10:1::15 465 Trying fd80:10:1::15... telnet: connect to address fd80:10:1::15: Connection refused
on each/every mail submit -- via dovecot -- dovecot makes the connection
2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-server: conn 10.1.2.163:35388 [1]: Server accepted connection (fd=7) 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-server: conn 10.1.2.163:35388 [1]: Connection created 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 [1]: Connection created 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 [1]: Disconnected
looks up IP address
2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 [1]: Looking up IP address 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 [1]: Performing asynchronous DNS lookup 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-server: conn 10.1.2.163:35388 [1]: Sent: 235 2.7.0 Logged in.
finds BOTH IPs -- IPv4 & IPv6
2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 [1]: DNS lookup successful; got 2 IPs
then first tries to connect via the host's IPv6 address,
2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 [1]: Connecting to fd80:10:1::15:465 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Connecting 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Waiting for connect (fd=8) to finish for max 0 msecs
############ FAILS ############
2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Client connection failed (fd=8)
then proceeds to connect to the host's IPv4 address
2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Connecting to 10.1.1.15:465 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Connecting 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Waiting for connect (fd=11) to finish for max 0 msecs 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Client connected (fd=11) 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Connected to server (from 10.1.1.15:52880) 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Starting SSL handshake 2021-04-03 19:35:35 submission(mailer@mx.example.com): Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: SSL handshake successful ...
and submission continues/completes
I need to get Dovecot to stop trying/failing @ those IPv6 address submission connections.
Either by
(1) trying IPv4 *first*, before IPv6, to avoid the FAIL on submission
or
(2) turning off submission relay by IPv6 altogether, as I'll never use it
What's the config required to do either/both?