ERROR: Could not open H.323 listener port on 1720

Make sure in /etc/asterisk/h323.conf you have correct ip in bindaddr line.

Example:

[general]
port = 1720
bindaddr = xxx.xxx.xxx.xxx

NOTE: Change to your correct server IP address here!

Also make sure no other process is listening on 1720 port:

netstat -vatupn

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Same solution when such CLI output when 'h323 set debug' is enabled:

[Sep 16 12:59:19] ERROR[3126]: rtp.c:1945 ast_rtp_new_with_bindaddr: Unexpected bind error: Cannot assign requested address
[Sep 16 12:59:19] WARNING[3126]: chan_h323.c:964 __oh323_rtp_create: Unable to create RTP session: Cannot assign requested address
[Sep 16 12:59:19] ERROR[3126]: chan_h323.c:1858 external_rtp_create: No RTP stream is available for call ip$localhost/24477 (24477)   ERROR: on_external_rtp_create failure
[Sep 16 12:59:19] ERROR[3126]: rtp.c:1945 ast_rtp_new_with_bindaddr: Unexpected bind error: Cannot assign requested address
[Sep 16 12:59:19] WARNING[3126]: chan_h323.c:964 __oh323_rtp_create: Unable to create RTP session: Cannot assign requested address
[Sep 16 12:59:19] ERROR[3126]: chan_h323.c:1858 external_rtp_create: No RTP stream is available for call ip$localhost/24477 (24477)   ERROR: on_external_rtp_create failure
[Sep 16 12:59:19] ERROR[3126]: rtp.c:1945 ast_rtp_new_with_bindaddr: Unexpected bind error: Cannot assign requested address
[Sep 16 12:59:19] WARNING[3126]: chan_h323.c:964 __oh323_rtp_create: Unable to create RTP session: Cannot assign requested address
[Sep 16 12:59:19] ERROR[3126]: chan_h323.c:1858 external_rtp_create: No RTP stream is available for call ip$localhost/24477 (24477)   ERROR: on_external_rtp_create failure
[Sep 16 12:59:19] ERROR[3126]: rtp.c:1945 ast_rtp_new_with_bindaddr: Unexpected bind error: Cannot assign requested address
[Sep 16 12:59:19] WARNING[3126]: chan_h323.c:964 __oh323_rtp_create: Unable to create RTP session: Cannot assign requested address
[Sep 16 12:59:19] ERROR[3126]: chan_h323.c:1858 external_rtp_create: No RTP stream is available for call ip$localhost/24477 (24477)   ERROR: on_external_rtp_create failure