There are 3 asterisks on the same subnet, how to merge them?

Question

Asterisk

Good afternoon.
There are 3 asterisks with different numbers from different providers. How can they be combined so that the ext. numbers could call each other?

Answer 1

For example:
For the first server, the numbers start from 1, for the 2nd server - from 2, for the 3rd server - from 3.
In iax.conf you will write the numbers.
We create a file in the main server with trunk settings (preferably a separate file).

[asterisk2]
host=IP_ADDRESS_1
type=friend
context=from-iax
qualify=yes
disallow=all
allow=alaw
allow=h261
allow=h263
allow=h263p
insecure=invite,port
canreinvite=no
nat=no

[asterisk3]
host=IP_ADDRESS_2
type=friend
context=from-iax
qualify=yes
disallow=all
allow=alaw
allow=h261
allow=h263
allow=h263p
insecure=invite,port
canreinvite=no
nat=no

Servers 2 and 3 have the same file but with a different set, respectively, i.e. for 1 server the trunk is up to the 2nd and 3rd, for the 2nd server the trunk is up to the 1st and 3rd, for the 3rd server the trunk is up to 1- th and 2nd.
Context - from-iax (for example)
In this context, we prescribe a rule for processing an incoming call for each server.
For the first server extensions.conf:

[from-iax]
exten => _1XX,n,DIAL(SIP/${EXTEN},,m)

For the second server extensions.conf:

[from-iax]
exten => _2XX,n,DIAL(SIP/${EXTEN},,m)

For the third server extensions.conf:

[from-iax]
exten => _3XX,n,DIAL(SIP/${EXTEN},,m)

For outgoing 1st server:

[external]
exten => _2XX,1,Dial(SIP/asterisk2/${EXTEN},,m)
exten => _3XX,1,Dial(SIP/asterisk3/${EXTEN},,m)

For outgoing 2nd server:

[external]
exten => _1XX,1,Dial(SIP/asterisk1/${EXTEN},,m)
exten => _3XX,1,Dial(SIP/asterisk3/${EXTEN},,m)

For outgoing 3rd server:

[external]
exten => _1XX,1,Dial(SIP/asterisk2/${EXTEN},,m)
exten => _2XX,1,Dial(SIP/asterisk3/${EXTEN},,m)

Answer 2

If the asterisks are in the same address space (there is no NAT between them), all this is achieved by adding sip.conf and the numbering plan. In the presence of NAT, things become a little more complicated.
The main issue is the development of a numbering plan and its structure. Selecting the method of calls to the city. Classic option for < 500 employees
- three-digit numbers
- exit to the city, starting with the city number from 9.
For further advice, you need the structure of your telephone network.