cs7-config.adoc: Improve doc on default SS7 SCTP addresses

Related: OS#5186
Change-Id: Ic8d9c00ae50907f1adad8f70b773e7b1362c4f50

1 files changed, 13 insertions, 3 deletions

diff --git a/common/chapters/cs7-config.adoc b/common/chapters/cs7-config.adoc
index 62e85bb..5ac9bae 100644
--- a/common/chapters/cs7-config.adoc
+++ b/common/chapters/cs7-config.adoc
@@ -76,9 +76,6 @@ for SCCP-level message exchange between all the connected programs.
 
 === Connect to STP Instance
 
-By default, an STP instance is assumed to listen on the default M3UA port
-(2905) on the local host (127.0.0.1).
-
 Establishing an SCCP/M3UA link towards a remote STP instance can be configured
 as:
 
@@ -93,6 +90,19 @@ cs7 instance 0
 
 Be aware that such an `asp` needs to be linked to an `as`, see <<as_and_asp>>.
 
+By default, an STP instance is assumed to listen on the default M3UA port
+(2905) on the local host. That means in general `127.0.0.1` will be used as
+default remote SCTP address, and `::1` will be added to the SCTP association if
+IPv6 support is available on the system.
+
+NOTE: OsmoSTP listens by default on `::` if IPv6 is enabled on the system,
+and on `0.0.0.0` otherwise. Address `::` actually superseeds `0.0.0.0`, meaning
+it will listen on all IPv4 and IPv6 addresses available on the system.
+
+CAUTION: Some applications overwrite the default target remote address to
+be `localhost`. If IPv6 support is available on the system, `localhost` will
+usually resolve to `::1`, otherwise it will usually resolve to `127.0.0.1`.
+
 === Local Point-Code
 
 Each CNI program on an SCCP/M3UA link typically has a local point-code,