Asterisk as a SIP client behind NAT - A Solution

[jcgalvezv]

Sometimes we need to configure asterisk as a SIP client behind a NAT. Common ways to solve this NAT issue is configuring externip=xxx.xxx.xxx.xxx and localnet=xxx.xxx.xxx.xxx where this last localnet use the form:

;localnet=192.168.0.0/255.255.0.0; All RFC 1918 addresses are local networks
;localnet=10.0.0.0/255.0.0.0 ; Also RFC1918
;localnet=172.16.0.0/12 ; Another RFC1918 with CIDR notation
;localnet=169.254.0.0/255.255.0.0 ;Zero conf local network

or something like:

localnet=192.168.1.1/24;

Everything would be just fine is the externip or External IP address remained always the same; but, some times this is not true because our ISP assigns us a dynamic public IP address that changes from time to time, or in the worst case a private IP address (like me).

To solve the previous issue we could, from time to time (really often), discover the new IP address and change the line externip=xxx.xxx.xxx.xxx in sip.conf file and issue a sip reload command in asterisk CLI; we could also use an automated procedure, as I did. A third option could be to use dyndns, something that cannot be done if you get a private IP address asigned.

I am going to explain how I solved this problem by using an automated procedure.

1. I changed the line

externip=xxx.xxx.xxx.xxx

for:

#include sip_externip.conf.

2. I wrote a script (with some help at the begining) that has changed. This is what I currently have (saved as checkexternip):

--------------------------------------------------------------------

# Get external IP address.

mynewip=`wget -O - http://checkip.dyndns.com|cut -b77-92|tr -d "</body>"`

# Get current Asterisk IP address.

myoldip=`dd if=/etc/asterisk/sip_externip.conf bs=9 skip=1 2>null`

if test .$myoldip != .$mynewip && !(test -z $mynewip)
then

echo "externip=$mynewip" > /etc/asterisk/sip_externip.conf
echo `date` "$mynewip" >> /etc/asterisk/sip_externip.log
asterisk -r -x "sip reload"

fi

-------------------------------------------------------------

This script checks for external IP changes, if changed rewrite sip_externip.conf, records the new IP address in sip_externip.log and asks asterisk to reaload sip configuration.

3. I wrote a cron entry like this:

*/1 * * * * /etc/asterisk/checkexternip

This cron entry executes the script once every minute so, my asterisk could be out of service (if my extern IP address changes) for maximum 1 minute. You must change /etc/asterisk/ with the path where you save your checkexternip script.

I hope this procedure can be usefull to someone else.

Juan C.

[rizsher]

A third option could be to use dyndns, something that cannot be done if you get a private IP address asigned.

Even with Dyndns, the IP address needs to be renever. Using Dyndns, I've got the following entries in my sip.conf

port = 5060           ; Port to bind to (SIP is 5060)
bindaddr = 0.0.0.0    ; Address to bind to (all addresses on machine)
externhost = mydyndnshost.freedomain.net
externrefresh = 5
localnet=192.168.1.1/255.255.255.0
nat=yes
defaultexpirey=3600

With this setup, my Dynamic IP has never created a problem for me; The externrefresh=5 setting makes sure I can be offline for a maximum of 5 minutes, this setting could be further reduced if desired. With this, there is no need for a script to be executed in cron.

I suppose jcgalvezv method could be used in a situation where a dyndns isn't available (though I guess pretty any router released in the last 3-4 years has a dynamic DNS clinet built in).