Q:

Asterisk:Registration is UNREACHABLE VOIP chan_sip.c:15171 sip_reg_timeout

I'm trying to register my VOIP but I can't and appear this massege
   [Jul 24 12:45:58] NOTICE[24430]: chan_sip.c:15171 sip_reg_timeout:    -- Registration for 'XXXXX@sip2.tellfree.net' timed out, trying again (Attempt #11)

When I use sip show peers
   tellfree/xxxxxx          xxx.xx.xxx.xx                               Auto (No)  No             5060     UNREACHABLE[/code]

But it happen suddenly. 
See my sip.conf 
   [general]
   allowguest=no
   autocreatepeer=no
   awayssauthreject=yes
   udpbindaddr=0.0.0.0:XXXX
   context=ramais
   externhost=XXXXXXXXXX.noip.us:XXXX
   localnet=192.1.1.2/255.255.255.0
   register => XXXXX:XXXX@sip2.tellfree.net:5060

   [tellfree]
   type=peer
   defaultuser=XXXXXXX
   secret=XXXXXXX
   context=ramais
   host=sip2.tellfree.net
   qualify=yes
   fromdomain=sip2.tellfree.net
   fromuser=XXXXXXXX
   allow=g729,ilbc,ulaw,alaw
   dtmfmode=rfc2833
   directmedia=no
   insecure=invite

A:

Can you ping sip2.tellfree.net from your server? If not, you have a network issue. 
If you can ping it, but it is unreachable from your Asterisk instance, then you have a configuration/Firewall issue. 
Either NAT, DNS, or SIP proxy would be my guess, but more information is needed to find out.

