Calling extensions between 2 freepbx

FreePBX Configuration
1

This one has me stumped…

I have 2 FreePBX servers
Server #1 has extension 999
Server #2 has extension 998

Server #1 has outbound route match=9XX

Both server’s trunks are context=from-internal

Server #1 is PJSIP with just the basic settings in the trunk
Auth=none
Reg=none
Server=192.168.61.11
Port=5060
Qualify=60

Server #2 is the old SIP with Incoming tab blank, and Outgoing tab like this:
type=peer
host=192.168.42.101
context=from-internal
qualify=yes
qualifyfreq=60

Both sides show that the trunk is up, qualify is good.

However, when I dial 998 from extension 999 on Server #1, I get “all circuits are busy”. It’s acting like when you have a from-trunk context and you are missing the inbound route. However, from-internal does not use inbound-route, right? It should work because the extension number exists, right?

Here is a condensed log from Server #2. Notice that is returns 401 Unauthorized.

<— SIP read from UDP:192.168.42.101:5060 —>
INVITE sip:[email protected]:5060 SIP/2.0
Via: SIP/2.0/UDP 192.168.42.101:5060;rport;branch=z9hG4bKPj84e18b24-cfdb-4f09-802f-bea030f52a77
From: “999” sip:[email protected];tag=5f8969bd-2f43-4516-9d4f-bad2cb89ec70
To: sip:[email protected]

Using INVITE request as basis request - accc86e7-5d2f-4adf-a06d-cb40b22aa8b1
Found peer ‘999’ for ‘999’ from 192.168.42.101:5060

<— Reliably Transmitting (no NAT) to 192.168.42.101:5060 —>
SIP/2.0 401 Unauthorized

2

Oh, I figured it out, but I don’t know why this matters. Maybe someone can tell me.

Server #2 also had an extension 999 … and therefore it was blocking Server #1 from sending from 999. When I deleted 999 from Server #2, then I was able to place a call from Server#1 ext 999 to Server #2 ext 998.

So, why does it fail when the server receiving a call has an extension number matching the remote calling extension number?

I realize that both servers cannot have the same TO extension (otherwise it would call the extension on the local server instead of using the outgoing route) but why can’t they both have the same FROM extension?