Author: Jeremy Harris Date: To: exim-users Subject: Re: [exim] Rate limiting connections
On 26/09/17 11:55, Robert Bannocks wrote: > In respect of smtp_accept_max is there some upper limit and, for RH Linux, how do I find out what this may be. There is presumably some Kernel limit, but there are other things to consider too. Is this just something people adjust hubristically or is there a more scientific approach?
I like the suggestion of hubris...
The kernel limitation is essentially 64k minus any reserved via
ip_local_port_range and ip_local_reserved_ports sysctls.
Exim has a hardcoded limit of 4k (obviously individual distros could
vary the code, but there's no support in build documentation for doing
so. Memory is pre-allocated for connection-tracking purposes in
proportion to the configured value, so you don't want it too high.
The practical limit will be your system load, dealing with the number
of concurrent connections.
>
> Same question for smtp_connect_backlog.
This is just the value given with the "listen" syscall to the kernel.
See the comments in the docs.
>
> Do not assume what I have inherited makes any sense.
If your problem is with certain individual source systems, consider
the smtp_max_per_host config option.
