When connected with peers running older versions of Asterisk, the following error might come up and inbound calls from the peer are rejected:
ERROR[xxxxx] chan_iax2.c: Call rejected, CallToken Support required. If unexpected, resolve by placing address x.x.x.x in the calltokenoptional list or setting user guest requirecalltoken=no
To resolve this, place the following in iax_custom.conf and reload Asterisk:
calltokenoptional=0.0.0.0/0.0.0.0;
add requirecalltoken=no in iax_additional.conf
as:
[501]
deny=0.0.0.0/0.0.0.0
type=friend
setvar=REALCALLERIDNUM=501
secret=501
qualify=yes
port=4569
permit=0.0.0.0/0.0.0.0
transfer=no
mailbox=501@device
host=dynamic
dial=IAX2/501
context=from-internal
callerid=device
accountcode=
requirecalltoken=no
Simply genius!!, nice way out for an annoying problem.