pfSense

When configuring remote a syslog server syslogd is invoked with the user selected interface binding if selected:

/usr/sbin/syslogd -O rfc3164 -s -c -c -l /var/dhcpd/var/run/log -P /var/run/syslog.pid -f /etc/syslog.conf -b 192.168.25.1

    <syslog>
        <filterdescriptions>1</filterdescriptions>
        <nentries>500</nentries>
        <logcompressiontype>none</logcompressiontype>
        <format>rfc3164</format>
        <rotatecount></rotatecount>
        <remoteserver>172.21.16.13:5140</remoteserver>
        <remoteserver2></remoteserver2>
        <remoteserver3></remoteserver3>
        <sourceip>lan</sourceip>
        <ipproto>ipv4</ipproto>
        <logall></logall>
        <logconfigchanges>enabled</logconfigchanges>
        <enable></enable>
    </syslog>

However in pfSense 2.8 that setting is ignored and the logically closest IP address is used as source instead:

WAN     udp     172.21.16.32:37402 -> 172.21.16.13:5140     SINGLE:NO_TRAFFIC     865 / 0     173 KiB / 0 B

This is a regression since 2.7.2