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Top Forums UNIX for Advanced & Expert Users Ha mailserver, is possible active/active with "constant" connection? Post 303045628 by hicksd8 on Saturday 4th of April 2020 02:09:53 PM
Old 04-04-2020
You problem is with network timeout settings; either the cluster or the clients.

Manually shutting down one of the cluster nodes may not give you the same result as a true CPU/power/whatever failure because the cluster software suite will probably see you do that. It would be better to simply pull out the RJ45 network connection to one of them simulating a network connection failure.

Anyway, the point is that a cluster failover takes time. During this time the virtual ip address is switched from one node to the other. Depending on the cluster suite this will take seconds/minutes. The fact that the client will reconnect to the surviving cluster node after you restart it proves that, had it waited long enough, it would have been able to reconnect on its own.

So the solution is to either (1) configure the cluster to failover faster, or (2) increase the timeout that clients will wait before giving up. That means that a new connection to the virtual ip address can be made before the configured timeout period ends.
 

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mxallowd(1)							   User Manuals 						       mxallowd(1)

NAME
mxallowd - dynamically whitelist your Mail eXchanger SYNOPSIS
mxallowd [-d] [-c configfile] [-t whitelist-time] [-p pflog-interface] [-l pcap-filter] [-F] [-s] [-q] [-p] -f fake-mailserver -r real- mailserver -n queue-num DESCRIPTION
mxallowd is a daemon which uses libnetfilter_queue (on Linux) or pf and pflog (on BSD) to allow (or deny) connections to a mailserver (or similar application) if the remote host hasn't connected to a fake daemon before. This is an improved version of the so-called nolisting (see http://www.nolisting.org/). The assumption is that spammers are not using RFC 2821-compatible SMTP-clients and are sending fire-and-forget spam (directly to the first or second MX-entry without retrying on error). This direct access is blocked with mxallowd, you'll only get a connection if you retry. NOTE: It is highly recommended to install nscd (nameserver caching daemon) or a similar software in order to speed-up DNS lookups. Since version 1.3, DNS lookups are done in a thread (so they don't block the main process), however, on very-high-traffic-sites, mxallowd may show significantly better overall performance in combination with nscd. OPTIONS
-b, --no-rdns-whitelist Disable whitelisting all IP-addresses that have the same RDNS as the connecting one (necessary for google mail) -c, --config Specifies an alternative configuration file (instead of /etc/mxallowd.conf) -t, --whitelist-time Specify the amount of time (in seconds) until an IP-address will be removed from the whitelist -s, --stdout Log to stdout, not to syslog -q, --quiet Don't log anything but errors. -f, --fake-mailserver Specify which IP-address the fake mailserver has (connecting to it will whitelist you for the real mailserver) -r, --real-mailserver Specify which IP-address the real mailserver has -F, --foreground Do not fork into background, stay on console -n, --queue-num (only available when compiled for netfilter_queue) Specify the queue number which will be used for the netfilter_queue-link. This has to be the same which is specified in the ipta- bles-rule and it has to be specified, there is no default. -p, --pflog-interface (only available when compiled for pf) Specify the pflog(4) interface which you configured in pf(4). The default is pflog0. Also see the pcap-filter-option if you use an interface which does not only get smtp-traffic. -l, --pcap-filter (only available when compiled for pf) Specify the filter for pcap. The default is "port 25". See tcpdump(8) for more information on the filters. FILES
/etc/mxallowd.conf System-wide configuration file. Use the long options without the beginning two dashes. For example: stdout fake-mailserver 192.168.1.3 fake-mailserver 192.168.1.4 real-mailserver 192.168.1.5 queue-num 23 EXAMPLES FOR NETFILTER
The machine has two IP-addresses. The mailserver only listens on 192.168.1.4, the nameserver returns the mx-records mx1.domain.com (192.168.1.3) with priority 5 and mx2.domain.com (192.168.1.4) with priority 10. # modprobe nfnetlink_queue # iptables -A INPUT -p tcp --dport 25 -m state --state NEW -j NFQUEUE --queue-num 23 # mxallowd -s -F -f 192.168.1.3 -r 192.168.1.4 -n 23 Then open a separate terminal and connect via telnet on your real mailserver. You'll see the connection attempt being dropped. Now connect to the fake mailserver and watch mxallowd's output. Afterwards, connect to the real mailserver to verify your mailserver is still working. EXAMPLES FOR PF
The machine has two IP-addresses. The mailserver only listens on 192.168.1.4, the nameserver returns the mx-records mx1.domain.com (192.168.1.3) with priority 5 and mx2.domain.com (192.168.1.4) with priority 10. Create a pf.conf like this: table <mx-white> persist real_mailserver="192.168.1.4" fake_mailserver="192.168.1.3" real_mailserver6="2001:dead:beef::1" fake_mailserver6="2001:dead:beef::2" pass in quick log on fxp0 proto tcp from <mx-white> to $real_mailserver port smtp pass in quick log on fxp0 inet6 proto tcp from <mx-white> to $real_mailserver6 port smtp block in log on fxp0 proto tcp to { $fake_mailserver $real_mailserver } port smtp block in log on fxp0 inet6 proto tcp to { $fake_mailserver6 $real_mailserver6 } port smtp Afterwards, load it and start mxallowd using the following commands: # pfctl -f /etc/pf.conf # mxallowd -s -F -f 192.168.1.3 -r 192.168.1.4 Then open a separate terminal and connect via telnet on your real mailserver. You'll see the connection attempt being dropped. Now connect to the fake mailserver and watch mxallowd's output. Afterwards, connect to the real mailserver to verify your mailserver is still working. The ruleset for pf is actually longer because pf does more than netfilter on linux -- netfilter passes the packets and lets mxallowd decide whether to drop/accept whilst pf blocks/passes before even "passing" to mxallowd. SEE ALSO
iptables(8), pf(4), pflog(4), tcpdump(8) AUTHOR
Michael Stapelberg <michael+mxallowd at stapelberg dot de> Linux MARCH 2012 mxallowd(1)
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