Thanks for your reply Frogmore42,
MQTT server and all connections are only from localhost. In fact, emonpi release is emonSD-03May16, and all componentes (redis, mosquitto, mqtt, node-red, etc) are on localhost.
But as you mention, IPv6 is enabled and maybe conections are connected on tcp6:
root@emonpi(rw):~# ifconfig -a
eth0 Link encap:Ethernet HWaddr b8:27:eb:0c:f9:2a
inet6 addr: fe80::3382:2ed7:366b:44fd/64 Scope:Link
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:49035768 errors:0 dropped:0 overruns:0 frame:0
TX packets:49035768 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:10711658352 (9.9 GiB) TX bytes:10711658352 (9.9 GiB)
wlan0 Link encap:Ethernet HWaddr b8:27:eb:59:ac:7f
inet addr:192.168.1.22 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::ebd3:2ca3:366a:f421/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1564311 errors:0 dropped:24 overruns:0 frame:0
TX packets:942294 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1767131566 (1.6 GiB) TX bytes:159406312 (152.0 MiB)
root@emonpi(rw):~# cat /etc/modprobe.d/ipv6.conf
# Don't load ipv6 by default
alias net-pf-10 off
#alias ipv6 off
root@emonpi(rw):~# netstat -lnpt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 905/sshd
tcp 0 0 0.0.0.0:1880 0.0.0.0:* LISTEN 548/node-red
tcp 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN 27064/0
tcp 0 0 0.0.0.0:1883 0.0.0.0:* LISTEN 25504/mosquitto
tcp 0 0 0.0.0.0:161 0.0.0.0:* LISTEN 1156/snmpd
tcp 0 0 0.0.0.0:5666 0.0.0.0:* LISTEN 7057/nrpe
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 1558/mysqld
tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 10673/redis-server
tcp 0 0 0.0.0.0:5038 0.0.0.0:* LISTEN 1803/asterisk
tcp 0 0 0.0.0.0:2000 0.0.0.0:* LISTEN 1803/asterisk
tcp6 0 0 :::5555 :::* LISTEN 10805/java
tcp6 0 0 :::22 :::* LISTEN 905/sshd
tcp6 0 0 ::1:6010 :::* LISTEN 27064/0
tcp6 0 0 :::1883 :::* LISTEN 25504/mosquitto
tcp6 0 0 :::8443 :::* LISTEN 10805/java
tcp6 0 0 :::5666 :::* LISTEN 7057/nrpe
tcp6 0 0 :::8080 :::* LISTEN 10805/java
tcp6 0 0 :::80 :::* LISTEN 1557/apache2
root@emonpi(rw):~# lsmod|grep ipv6
nf_reject_ipv6 3729 1 ip6t_REJECT
nf_log_ipv6 5412 5
nf_conntrack_ipv6 9161 7
nf_defrag_ipv6 15842 1 nf_conntrack_ipv6
nf_log_common 4521 2 nf_log_ipv6,nf_log_ipv4
nf_conntrack 104634 8 nf_conntrack_ipv6,nf_conntrack_ftp,nf_conntrack_ipv4,nf_conntrack_broadcast,nf_nat_ftp,nf_conntrack_netbios_ns,xt_conntrack,nf_nat
ipv6 408900 67 nf_conntrack_ipv6,nf_reject_ipv6,nf_defrag_ipv6
After implement notes in following link, seems that IPv6 is disabled
https://www.raspberrypi.org/forums/viewtopic.php?t=138899
root@emonpi(ro):~# ifconfig -a
eth0 Link encap:Ethernet HWaddr b8:27:eb:0c:f9:2a
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:1353 errors:0 dropped:0 overruns:0 frame:0
TX packets:1353 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:163287 (159.4 KiB) TX bytes:163287 (159.4 KiB)
wlan0 Link encap:Ethernet HWaddr b8:27:eb:59:ac:7f
inet addr:192.168.1.22 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:157 errors:0 dropped:0 overruns:0 frame:0
TX packets:146 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:14606 (14.2 KiB) TX bytes:26743 (26.1 KiB)
root@emonpi(ro):~#
root@emonpi(ro):~# netstat -lnpt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:5555 0.0.0.0:* LISTEN 1148/java
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 907/sshd
tcp 0 0 0.0.0.0:1880 0.0.0.0:* LISTEN 535/node-red
tcp 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN 1910/0
tcp 0 0 0.0.0.0:8443 0.0.0.0:* LISTEN 1148/java
tcp 0 0 0.0.0.0:1883 0.0.0.0:* LISTEN 533/mosquitto
tcp 0 0 0.0.0.0:161 0.0.0.0:* LISTEN 1150/snmpd
tcp 0 0 0.0.0.0:5666 0.0.0.0:* LISTEN 1031/nrpe
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 1547/mysqld
tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 975/redis-server 12
tcp 0 0 0.0.0.0:5038 0.0.0.0:* LISTEN 1787/asterisk
tcp 0 0 0.0.0.0:2000 0.0.0.0:* LISTEN 1787/asterisk
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 1148/java
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 1517/apache2
I will cross my fingers and hope this solve the issue. 