Multiple Transport Objects Of Same Protocol In Pjsip.conf

Home » Asterisk Users » Multiple Transport Objects Of Same Protocol In Pjsip.conf
Asterisk Users 2 Comments


Our Asterisk 13 PBX (on network, bound to is behind a NAT, acting as a client to our ITSPs SIP server. But also, this Asterisk is server for various VoIP telephones.

Acoording to Asterisk’s wiki, the transport section of pjsip.conf is configured as follows:

; Transport via UDP
type= transport protocol= udp local_net=
external_media_address= ddns.gdr external_signaling_address= ddns.gdr

The VoIP phones are also residing on network, bu they are separated and strictly prohibited by firewall rules to act with the outer net. The Asterisk PBX is acting as the transition point between our VoIP phones and the ITSPs SIP server.

So, my understanding is that for NAT, the transport is recommended to be configured as shown above. But what is about the transport with the phones “inside”?

I’m new to Asterisk, and from the “naiv” understanding of what I extracted from the sparse documentation on that subject, for each endpoint associated with a phone, I need transport. The protocol used by the phones is UDP, but no NAT. So, I did create a new transport section, like

type= transport protocol= udp bind=

This results immediately in an error due to the bind= attribute. Asterisk bails out at havind the address already in use. In fact, it is the trunk/endpoint consuming the, and since the VoIP phones are all in, this results obviously in an error. This is surprising me 🙁

How to deal with this without adding more network complexity like routing (by putting the phones into a subnet or other network)?

Kind regards,


2 thoughts on - Multiple Transport Objects Of Same Protocol In Pjsip.conf

  • You should only need this single transport as it will get used by everything. Only when contacting external things will the external values be used instead. This is determined based on the “local_net”
    values you’ve provided.

  • Also, setting a transport to expect NAT, when in fact there isn’t any, won’t cause problems.

    Telling Asterisk to expect NAT simply means that it pays attention to where the packets come from, not what addresses they contain inside them.

    If you have no NAT, these two addresses are the same, so no harm done.