config: set marker_listen_port default to 3070 and document in config templates

Change the marker UDP sink default from port=0 (OS-chosen) to 3070 for
predictable firewall/debugging/monitoring.

Add marker_listen_host and marker_listen_port with documentation to
config_samples/gns3_server.conf and scripts/gns3_server.conf.

gns3server/config_samples/gns3_server.conf

@@ -92,6 +92,13 @@ udp_end_port_range = 30000
 ; uBridge executable location, default: search in PATH
 ;ubridge_path = ubridge
 
+; Marker (traffic-insight) UDP sink: one listener per compute process that
+; receives uBridge MARK signals from every uBridge on this host.
+; marker_listen_host defaults to 127.0.0.1 because uBridge runs locally.
+; marker_listen_port defaults to 3070 (set to 0 for OS-chosen).
+;marker_listen_host = 127.0.0.1
+;marker_listen_port = 3070
+
 ; Option to enable or disable compute HTTP authentication
 enable_http_auth = True
 

gns3server/schemas/config.py

@@ -158,7 +158,7 @@ class ServerSettings(BaseModel):
     # defaults to loopback because ubridge runs on the same host as the compute.
     # port=0 lets the OS choose a free port (read back and handed to ubridge).
     marker_listen_host: str = "127.0.0.1"
-    marker_listen_port: int = Field(0, ge=0, le=65535)
+    marker_listen_port: int = Field(3070, ge=0, le=65535)
     compute_username: str = "gns3"
     compute_password: SecretStr = SecretStr("")
     allowed_interfaces: List[str] = Field(default_factory=list)

scripts/gns3_server.conf

@@ -4,3 +4,7 @@ compute_password = gns3
 skills_repo_url = https://github.com/yueguobin/GNS3-Skills.git
 skills_repo_branch = main
 skills_auto_update = false
+
+; Marker (traffic-insight) UDP sink port for uBridge MARK signals
+; Set to 0 for OS-chosen port
+marker_listen_port = 3070