Subj : Automatically blocking co
To   : Dumas Walker
From : Digital Man
Date : Thu Jun 06 2024 01:50 pm

  Re: Automatically blocking co
  By: Dumas Walker to DIGITAL MAN on Thu Jun 06 2024 09:23 am

 > >  > > I have not observed this problem (Telnet server not responding while
 > >  > > SSH does)
 > >  > > nor heard any reports of it, besides yours. I would expect the use of
 > >  > > tools like netstat to help identify the real cause of that issue.
 >
 > >  > If I can restart synchronet and it goes away, I think that tells me
 > >  > something.
 >
 > > It tells me that the TCP port was rebound. If the socket is configured for
 > > address/port reuse (in ctrl/sockopts.ini), then one could artifically
 > > create this exact scenario by starting and stopping a second process
 > > (after sbbs) tha
 > > bound to TCP port 23. It could even be a second instance of sbbs. No
 > > "crashing
 > > of the Synchronet telnet server would be required.
 >
 > Hmmmm... which setting would I want to set if I wanted to tell synchronet
 > not to allow the port to be reused by another process?

On Linux, that'd be REUSEADDR = FALSE

 > Currently, the only two options I have set in sockopts.ini are:
 >
 > KEEPALIVE = TRUE
 > TCP_NODELAY = TRUE
 >
 > I also see that IPV6_V6ONLY = 1 .  What does that one do?

From https://www.man7.org/linux/man-pages/man7/ipv6.7.html

       IPV6_V6ONLY (since Linux 2.4.21 and 2.6)
              If this flag is set to true (nonzero), then the socket is
              restricted to sending and receiving IPv6 packets only.  In
              this case, an IPv4 and an IPv6 application can bind to a
              single port at the same time.

              If this flag is set to false (zero), then the socket can
              be used to send and receive packets to and from an IPv6
              address or an IPv4-mapped IPv6 address.

              The argument is a pointer to a boolean value in an
              integer.

              The default value for this flag is defined by the contents
              of the file /proc/sys/net/ipv6/bindv6only.  The default
              value for that file is 0 (false).

 > I suspect that these are all defaults as I don't remember changing anything
 > in this ini file, and the modify date is 8/20/2015.

Yes, looks like defaults.
-- 
                                            digital man (rob)

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